Showing papers on "Root hair published in 2019"
TL;DR: This work grew a worldwide panel of replicated Arabidopsis thaliana accessions outdoors and over winter to characterize their root-microbial communities, and found evidence that fungi have a strong influence on the structure of the root microbiome.
Abstract: Roots provide plants mineral nutrients and stability in soil; while doing so, they come into contact with diverse soil microbes that affect plant health and productivity. Despite their ecological and agricultural relevance, the factors that shape the root microbiome remain poorly understood. We grew a worldwide panel of replicated Arabidopsis thaliana accessions outdoors and over winter to characterize their root-microbial communities. Although studies of the root microbiome tend to focus on bacteria, we found evidence that fungi have a strong influence on the structure of the root microbiome. Moreover, host effects appear to have a stronger influence on plant-fungal communities than plant-bacterial communities. Mapping the host genes that affect microbiome traits identified a priori candidate genes with roles in plant immunity; the root microbiome also appears to be strongly affected by genes that impact root and root hair development. Our results suggest that future analyses of the root microbiome should focus on multiple kingdoms, and that the root microbiome is shaped not only by genes involved in defense, but also by genes involved in plant form and physiology.
118 citations
TL;DR: The results demonstrate that the KAI2 signalling pathway is an important new regulator of root hair and root development in Arabidopsis and lay an important basis for research into a molecular understanding of how very similar and partially overlapping hormone signalling pathways regulate different phenotypic outputs.
Abstract: Karrikins are smoke-derived compounds presumed to mimic endogenous signalling molecules (KAI2-ligand, KL), whose signalling pathway is closely related to that of strigolactones (SLs), important regulators of plant development. Both karrikins/KLs and SLs are perceived by closely related α/β hydrolase receptors (KAI2 and D14 respectively), and signalling through both receptors requires the F-box protein MAX2. Furthermore, both pathways trigger proteasome-mediated degradation of related SMAX1-LIKE (SMXL) proteins, to influence development. It has previously been suggested in multiple studies that SLs are important regulators of root and root hair development in Arabidopsis, but these conclusions are based on phenotypes observed in the non-specific max2 mutants and by use of racemic-GR24, a mixture of stereoisomers that activates both D14 and KAI2 signalling pathways. Here, we demonstrate that the majority of the effects on Arabidopsis root development previously attributed to SL signalling are actually mediated by the KAI2 signalling pathway. Using mutants defective in SL or KL synthesis and/or perception, we show that KAI2-mediated signalling alone regulates root hair density and root hair length as well as root skewing, straightness and diameter, while both KAI2 and D14 pathways regulate lateral root density and epidermal cell length. We test the key hypothesis that KAI2 signals by a non-canonical receptor-target mechanism in the context of root development. Our results provide no evidence for this, and we instead show that all effects of KAI2 in the root can be explained by canonical SMAX1/SMXL2 activity. However, we do find evidence for non-canonical GR24 ligand-receptor interactions in D14/KAI2-mediated root hair development. Overall, our results demonstrate that the KAI2 signalling pathway is an important new regulator of root hair and root development in Arabidopsis and lay an important basis for research into a molecular understanding of how very similar and partially overlapping hormone signalling pathways regulate different phenotypic outputs.
108 citations
TL;DR: The current understanding of the developmental roles of AUX1/LAX gene family is summarized and the modelling approaches that are providing new insight into the role of auxin transport in plant development are discussed.
Abstract: Plant hormone auxin regulates several aspects of plant growth and development. Auxin is predominantly synthesized in the shoot apex and developing leaf primordia and from there it is transported to the target tissues e.g. roots. Auxin transport is polar in nature and is carrier-mediated. AUXIN1/LIKE-AUX1 (AUX1/LAX) family members are the major auxin influx carriers whereas PIN-FORMED (PIN) family and some members of the P-GLYCOPROTEIN/ATP-BINDING CASSETTE B4 (PGP/ABCB) family are major auxin efflux carriers. AUX1/LAX auxin influx carriers are multi-membrane spanning transmembrane proteins sharing similarity to amino acid permeases. Mutations in AUX1/LAX genes result in auxin related developmental defects and have been implicated in regulating key plant processes including root and lateral root development, root gravitropism, root hair development, vascular patterning, seed germination, apical hook formation, leaf morphogenesis, phyllotactic patterning, female gametophyte development and embryo development. Recently AUX1 has also been implicated in regulating plant responses to abiotic stresses. This review summarizes our current understanding of the developmental roles of AUX1/LAX gene family and will also briefly discuss the modelling approaches that are providing new insight into the role of auxin transport in plant development.
96 citations
TL;DR: How co-ordination of TOR-mediated light and hormone signalling is involved in root and shoot apical meristem activation, proliferation of leaf primordia, cotyledon/leaf greening, and hypocotyl elongation is explored.
Abstract: The multidomain target of rapamycin (TOR) is an atypical serine/threonine protein kinase resembling phosphatidylinositol lipid kinases, but retains high sequence identity and serves a remarkably conserved role as a master signalling integrator in yeasts, plants, and humans. TOR dynamically orchestrates cell metabolism, biogenesis, organ growth, and development transitions in response to nutrient, energy, hormone, and environmental cues. Here we review recent findings on the versatile and complex roles of TOR in transcriptome reprogramming, seedling, root, and shoot growth, and root hair production activated by sugar and energy signalling. We explore how co-ordination of TOR-mediated light and hormone signalling is involved in root and shoot apical meristem activation, proliferation of leaf primordia, cotyledon/leaf greening, and hypocotyl elongation. We also discuss the emerging TOR functions in response to sulfur assimilation and metabolism and consider potential molecular links and positive feedback loops between TOR, sugar, energy, and other essential macronutrients.
93 citations
TL;DR: Progress is described in the identification of genes and regulatory pathways involved in the development of root systems in rice (Oryza sativa L.), including crown roots, lateral roots, root hairs, and root length.
Abstract: Roots are fundamentally important for growth and development, anchoring the plant to its growth substrate, facilitating water and nutrient uptake from the soil, and sensing and responding to environmental signals such as biotic and abiotic stresses. Understanding the molecular mechanisms controlling root architecture is essential for improving nutrient uptake efficiency and crop yields. In this review, we describe the progress being made in the identification of genes and regulatory pathways involved in the development of root systems in rice (Oryza sativa L.), including crown roots, lateral roots, root hairs, and root length. Genes involved in the adaptation of roots to the environmental nutrient status are reviewed, and strategies for further study and agricultural applications are discussed. The growth and development of rice roots are controlled by both genetic factors and environmental cues. Plant hormones, especially auxin and cytokinin, play important roles in root growth and development. Understanding the molecular mechanisms regulating root architecture and response to environmental signals can contribute to the genetic improvement of crop root systems, enhancing their adaptation to stressful environmental conditions.
89 citations
TL;DR: The results show that the application of Cra20 changes the rhizosphere indigenous bacterial community, which may be due to the change in root structure, and provide new insights into the complex mechanisms of plant and bacterial interactions.
Abstract: The rhizosphere is colonized by a mass of microbes, including bacteria capable of promoting plant growth that carry out complex interactions. Here, by using a sterile experimental system, we demonstrate that Sphingomonas sp. Cra20 promotes the growth of Arabidopsis thaliana by driving developmental plasticity in the roots, thus stimulating the growth of lateral roots and root hairs. By investigating the growth dynamics of A. thaliana in soil with different water-content, we demonstrate that Cra20 increases the growth rate of plants, but does not change the time of reproductive transition under well-water condition. The results further show that the application of Cra20 changes the rhizosphere indigenous bacterial community, which may be due to the change in root structure. Our findings provide new insights into the complex mechanisms of plant and bacterial interactions. The ability to promote the growth of plants under water-deficit can contribute to the development of sustainable agriculture.
89 citations
TL;DR: The timing of the growth machinery assembly in polarizing hair cells is dissected and it is found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factors (GEFs).
67 citations
TL;DR: It is reported that direct illumination of the root surface with blue light is critical and sufficient for the Pi deficiency-induced inhibition of PR growth of Arabidopsis seedlings and demonstrated that this developmental change is not an active cellular response; instead, it is a phenotype resulting from growth in transparent Petri dishes.
66 citations
27 Jun 2019
TL;DR: An increase in estimated root surface area by 20% under salt stress conditions indicated that the spontaneous responses of plants to uptake more water and nutrients allowed a plant to cope with stressful conditions.
Abstract: Plant roots show morphological plasticity and play a substantial role in tolerance to various edaphic stresses. The aim of this study was to explore salinity-induced morphogenic responses of root traits and root hairs of two rapeseed varieties, BARI Sarisha-8 and Binasarisha-5, at the reproductive stage and perceive the effects on their reproductive growth. The experiment was conducted in a hydroponic culture. Two treatments, 0 mM NaCl as control and 100 mM NaCl, were imposed 55 d after germination. Plants exposed to 100 mM NaCl for seven days displayed greater damage in the leaves, flowers, and siliquae compared to control. Length of root hairs on first-order and third-order lateral roots, density of root hairs on first-order lateral roots, and length of third-order lateral roots were significantly greater by 91%, 22%, 29%, and 48%, respectively, in the treated condition compared to the control. An increase in estimated root surface area by 20% under salt stress conditions indicated that the spontaneous responses of plants to uptake more water and nutrients allowed a plant to cope with stressful conditions. The results of this study suggest that any future stress breeding programs should consider plasticity of root traits intensively.
60 citations
TL;DR: How plants integrate phytohormonal and environmental signals, such as auxin, ethylene and phosphate availability, and modulate the level of these transcriptional regulators to tune root hair development is discussed.
Abstract: Root hairs play important roles for the acquisition of nutrients, microbe interaction and plant anchorage. In addition, root hairs provide an excellent model system to study cell patterning, differentiation and growth. Arabidopsis root hairs have been thoroughly studied to understand how plants regulate cell fate and growth in response to environmental signals. Accumulating evidence suggests that a multi-layered gene regulatory network is the molecular secret to enable the flexible and adequate response to multiple signals. In this review, we describe the key transcriptional regulators controlling cell fate and/or cell growth of root hairs. We also discuss how plants integrate phytohormonal and environmental signals, such as auxin, ethylene and phosphate availability, and modulate the level of these transcriptional regulators to tune root hair development.
60 citations
TL;DR: It is concluded that mycorrhizal plants possessed better root-hair growth to adapt mild DS, which is associated with mycor rhizal colonization and endogenous hormone changes.
Abstract: A pot experiment was used to evaluate the effects of an arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae on plant growth performance, root-hair growth, and root hormone levels in trifoliat...
TL;DR: It is proposed that Pi-starved plants increase the cZ/tZ ratio to maintain basal CK responses and allocate Pi in the root system to sustain its growth.
Abstract: Phosphate (Pi) is an essential nutrient for all organisms. Roots are underground organs, but the majority of the root biology studies have been done on root systems growing in the presence of light. Root illumination alters the Pi starvation response (PSR) at different intensities. Thus, we have analyzed morphological, transcriptional and physiological responses to Pi starvation in dark-grown roots. We have identified new genes and pathways regulated by Pi starvation that were not described previously. We also show that Pi-starved plants increase the cis-zeatin (cZ) : trans-zeatin (tZ) ratio. Transcriptomic analyses show that tZ preferentially represses cell cycle and PSR genes, whereas cZ induces genes involved in cell and root hair elongation and differentiation. In fact, cZ-treated seedlings show longer root system as well as longer root hairs compared with tZ-treated seedlings, increasing the total absorbing surface. Mutants with low cZ concentrations do not allocate free Pi in roots during Pi starvation. We propose that Pi-starved plants increase the cZ : tZ ratio to maintain basal cytokinin responses and allocate Pi in the root system to sustain its growth. Therefore, cZ acts as a PSR hormone that stimulates root and root hair elongation to enlarge the root absorbing surface and to increase Pi concentrations in roots.
TL;DR: It is determined that a soil moisture level of 10%-14% (w/w) stimulated greater rhizosheath production compared to other soil moisture levels, and root hair density and length increased at this soil moisturelevel, which was validated by measurement of the expression of root hair-related genes.
Abstract: The rhizosheath, a layer of soil particles that adheres firmly to the root surface by a combination of root hairs and mucilage, may improve tolerance to drought stress. Setaria italica (L.) P. Beauv. (foxtail millet), a member of the Poaceae family, is an important food and fodder crop in arid regions and forms a larger rhizosheath under drought conditions. Rhizosheath formation under drought conditions has been studied, but the regulation of root hair growth and rhizosheath size in response to soil moisture remains unclear. To address this question, in this study we monitored root hair growth and rhizosheath development in response to a gradual decline in soil moisture. Here, we determined that a soil moisture level of 10%-14% (w/w) stimulated greater rhizosheath production compared to other soil moisture levels. Root hair density and length also increased at this soil moisture level, which was validated by measurement of the expression of root hair-related genes. These findings contribute to our understanding of rhizosheath formation in response to soil water stress.
TL;DR: In this paper, the authors used an RNA-guided Cas9 system to assess the possibility of increasing the grain yield of barley by knocking out CKX genes, while no changes in grain yield were observed in either mutant line.
Abstract: Barley is among four of the most important cereal crops with respect to global production. Increasing barley yields to desired levels can be achieved by the genetic manipulation of cytokinin content. Cytokinins are plant hormones that regulate many developmental processes and have a strong influence on grain yield. Cytokinin homeostasis is regulated by members of several multigene families. CKX genes encode the cytokinin oxidase/dehydrogenase enzyme, which catalyzes the irreversible degradation of cytokinin. Several recent studies have demonstrated that the RNAi-based silencing of CKX genes leads to increased grain yields in some crop species. To assess the possibility of increasing the grain yield of barley by knocking out CKX genes, we used an RNA-guided Cas9 system to generate ckx1 and ckx3 mutant lines with knockout mutations in the HvCKX1 and HvCKX3 genes, respectively. Homozygous, transgene-free mutant lines were subsequently selected and analyzed. A significant decrease in CKX enzyme activity was observed in the spikes of the ckx1 lines, while in the ckx3 lines, the activity remained at a similar level to that in the control plants. Despite these differences, no changes in grain yield were observed in either mutant line. In turn, differences in CKX activity in the roots between the ckx1 and ckx3 mutants were reflected via root morphology. The decreased CKX activity in the ckx1 lines corresponded to greater root length, increased surface area, and greater numbers of root hairs, while the increased CKX activity in the ckx3 mutants gave the opposite results. RNA-seq analysis of the spike and root transcriptomes revealed an altered regulation of genes controlling cytokinin metabolism and signaling, as well as other genes that are important during seed development, such as those that encode nutrient transporters. The observed changes suggest that the knockout of a single CKX gene in barley may be not sufficient for disrupting cytokinin homeostasis or increasing grain yields.
TL;DR: It is suggested that OsPIN1a and Ospin1b are involved in root, shoot and inflorescence development in rice, whereas Os PIN1c and OsPin1d mainly function in panicle formation.
Abstract: Auxin is a phytohormone that plays an important role in plant growth and development by forming local concentration gradients. The regulation of auxin levels is determined by the activity of auxin efflux carrier protein PIN-formed (PIN). In Arabidopsis thaliana, PIN-formed1 (PIN1) functions in inflorescence and root development. In rice (Oryza sativa L.), there are four PIN1 homologs (OsPIN1a-1d), but their functions remain largely unexplored. Hence, in this study, we created mutant alleles of PIN1 gene-pin1a, pin1b, pin1c, pin1d, pin1a pin1b and pin1c pin1d- using CRISPR/Cas9 technology and used them to study the functions of the four OsPIN1 paralogs in rice. In wild-type rice, all four OsPIN1 genes were relatively highly expressed in the root than in other tissues. Compared with the wild type, the OsPIN1 single mutants had no dramatic phenotypes, but the pin1a pin1b double mutant had shorter shoots and primary roots, fewer crown roots, reduced root gravitropism, longer root hairs and larger panicle branch angle. Furthermore, the pin1c pin1d double mutant showed no observable phenotype at the seedling stage, but showed naked, pin-shape inflorescence at flowering. These data suggest that OsPIN1a and OsPIN1b are involved in root, shoot and inflorescence development in rice, whereas OsPIN1c and OsPIN1d mainly function in panicle formation. Our study provides basic knowledge that will facilitate the study of auxin transport and signaling in rice.
TL;DR: A model is proposed that describes the variation in porosity near roots taking into account soil compaction and the surface effect at the root surface, hypothesised to cause the observed increased pore volume fraction immediately next to the epidermis.
Abstract: Soil adjacent to roots has distinct structural and physical properties from bulk soil, affecting water and solute acquisition by plants. Detailed knowledge on how root activity and traits such as root hairs affect the 3D pore structure at a fine scale is scarce and often contradictory.
Roots of hairless barley (Hordeum vulgare L. cv ‘Optic’) mutant (NRH) and its wildtype (WT) parent were grown in tubes of sieved (<250 μm) sandy loam soil under two different water regimes. The tubes were scanned with synchrotron based X‐ray CT to visualise pore structure at the soil‐root interface. Pore volume fraction and pore size distribution were analysed versus distance within 1 mm of the root surface.
Less dense packing packing of particles at the root‐surface was hypothesised to cause the observed increased pore volume fraction immediately next to the epidermis. The pore size distribution was narrower due to a decreased fraction of larger pores. There were no statistically significant differences in pore structure between genotypes or moisture conditions.
A model is proposed that describes the variation in porosity near roots taking into account soil compaction and the surface effect at the root surface.
TL;DR: The data indicate that R bohs possess different ranges of enzymatic activity, and that some Rbohs have evolved to carry specific functions in cell growth.
Abstract: Reactive oxygen species (ROS) produced by NADPH oxidases, called respiratory burst oxidase homologs (Rbohs), play crucial roles in development as well as biotic and abiotic stress responses in plants. Arabidopsis has 10 Rboh genes, AtRbohA to AtRbohJ. Five AtRbohs (AtRbohC, -D, -F, -H and -J) are synergistically activated by Ca2+ -binding and protein phosphorylation to produce ROS that play various roles in planta, although the activities of the other Rbohs remain unknown. With a heterologous expression system, we found a range of ROS-producing activity among the AtRbohs with differences up to 100 times, indicating that the required amounts of ROS are different in each situation where AtRbohs act. To specify the functions of AtRbohs involved in cell growth, we focused on AtRbohC, -H and -J, which are involved in tip growth of root hairs or pollen tubes. Ectopic expression of the root hair factor AtRbohC/ROOT HAIR DEFECTIVE 2 (RHD2) in pollen tubes restored the atrbohH atrbohJ defects in tip growth of pollen tubes. However, expression of AtRbohH or -J in root hairs did not complement the tip growth defect in the atrbohC/rhd2 mutant. Our data indicate that Rbohs possess different ranges of enzymatic activity, and that some Rbohs have evolved to carry specific functions in cell growth.
TL;DR: The reproducibility of plant trait changes in response to three growth environments is investigated, finding plants grown in soil extract were morphologically and metabolically distinct, with root hairs four times longer than with other growth conditions.
Abstract: There is a dynamic reciprocity between plants and their environment: soil physiochemical properties influence plant morphology and metabolism, and root morphology and exudates shape the environment surrounding roots. Here, we investigate the reproducibility of plant trait changes in response to three growth environments. We utilized fabricated ecosystem (EcoFAB) devices to grow the model grass Brachypodium distachyon in three distinct media across four laboratories: phosphate-sufficient and -deficient mineral media allowed assessment of the effects of phosphate starvation, and a complex, sterile soil extract represented a more natural environment with yet uncharacterized effects on plant growth and metabolism. Tissue weight and phosphate content, total root length, and root tissue and exudate metabolic profiles were consistent across laboratories and distinct between experimental treatments. Plants grown in soil extract were morphologically and metabolically distinct, with root hairs four times longer than with other growth conditions. Further, plants depleted half of the metabolites investigated from the soil extract. To interact with their environment, plants not only adapt morphology and release complex metabolite mixtures, but also selectively deplete a range of soil-derived metabolites. The EcoFABs utilized here generated high interlaboratory reproducibility, demonstrating their value in standardized investigations of plant traits.
TL;DR: The auxin biosynthesis gene, GmYUC2a, is required for root and nodule development in soybean, showing that local auxin biolysis contributes significantly to determine nodules development.
Abstract: Auxin plays central roles in rhizobial infection and nodule development in legumes. However, the sources of auxin during nodulation are unknown. In this study, we analyzed the YUCCA (YUC) gene family of soybean and identified GmYUC2a as an important regulator of auxin biosynthesis that modulates nodulation. Following rhizobial infection, GmYUC2a exhibited increased expression in various nodule tissues. Overexpression of GmYUC2a (35S::GmYUC2a) increased auxin production in soybean, resulting in severe growth defects in root hairs and root development. Upon rhizobial infection, 35S::GmYUC2a hairy roots displayed altered patterns of root hair deformation and nodule formation. Root hair deformation occurred mainly on primary roots, and nodules formed exclusively on primary roots of 35S::GmYUC2a plants. Moreover, transgenic 35S::GmYUC2a composite plants showed delayed nodule development and a reduced number of nodules. Our results suggest that GmYUC2a plays an important role in regulating both root growth and nodulation by modulating auxin balance in soybean.
TL;DR: A novel pathway alleviating Al-induced oxidative damage by inhibition of acropetal auxin transport is uncovered and provides a new option for engineering Al-tolerant rice species.
Abstract: In rice, there are five members of the auxin carrier AUXIN1/LIKE AUX1 family; however, the biological functions of the other four members besides OsAUX1 remain unknown. Here, by using CRISPR/Cas9, we constructed two independent OsAUX3 knock-down lines, osaux3-1 and osaux3-2, in wild-type rice, Hwayoung (WT/HY) and Dongjin (WT/DJ). osaux3-1 and osaux3-2 have shorter primary roots (PRs), decreased lateral root (LR) density, and longer root hairs (RHs) compared with their WT. OsAUX3 expression in PRs, LRs, and RHs further supports that OsAUX3 plays a critical role in the regulation of root development. OsAUX3 locates at the plasma membrane and functions as an auxin influx carrier affecting acropetal auxin transport. OsAUX3 is up-regulated in the root apex under aluminium (Al) stress, and osaux3-2 is insensitive to Al treatments. Furthermore, 1-naphthylacetic acid accented the sensitivity of WT/DJ and osaux3-2 to respond to Al stress. Auxin concentrations, Al contents, and Al-induced reactive oxygen species-mediated damage in osaux3-2 under Al stress are lower than in WT, indicating that OsAUX3 is involved in Al-induced inhibition of root growth. This study uncovers a novel pathway alleviating Al-induced oxidative damage by inhibition of acropetal auxin transport and provides a new option for engineering Al-tolerant rice species.
TL;DR: It is shown that the ectomycorrhizal fungus L. bicolor produces an array of lipochitooligosaccharides (LCOs) that can trigger both root hair branching in legumes and calcium spiking in the host plant Populus in a CASTOR/POLLUX-dependent manner.
Abstract: Mycorrhizal fungi form mutualistic associations with the roots of most land plants and provide them with mineral nutrients from the soil in exchange for fixed carbon derived from photosynthesis. The common symbiosis pathway (CSP) is a conserved molecular signaling pathway in all plants capable of associating with arbuscular mycorrhizal fungi. It is required not only for arbuscular mycorrhizal symbiosis but also for rhizobia-legume and actinorhizal symbioses. Given its role in such diverse symbiotic associations, we hypothesized that the CSP also plays a role in ectomycorrhizal associations. We showed that the ectomycorrhizal fungus Laccaria bicolor produces an array of lipochitooligosaccharides (LCOs) that can trigger both root hair branching in legumes and, most importantly, calcium spiking in the host plant Populus in a CASTOR/POLLUX-dependent manner. Nonsulfated LCOs enhanced lateral root development in Populus in a calcium/calmodulin-dependent protein kinase (CCaMK)-dependent manner, and sulfated LCOs enhanced the colonization of Populus by L. bicolor Compared with the wild-type Populus, the colonization of CASTOR/POLLUX and CCaMK RNA interference lines by L. bicolor was reduced. Our work demonstrates that similar to other root symbioses, L. bicolor uses the CSP for the full establishment of its mutualistic association with Populus.
TL;DR: The results suggest that these calmodulin-binding and Ca2+ -permeable channels organize a robust tip-focused oscillatory calcium gradient, which is not essential for root hair initiation but is required to control the integrity of the root hair after the transition to the rapid growth phase.
Abstract: Calcium gradients underlie polarization in eukaryotic cells. In plants, a tip-focused Ca2+ -gradient is fundamental for rapid and unidirectional cell expansion during epidermal root hair development. Here we report that three members of the cyclic nucleotide-gated channel family are required to maintain cytosolic Ca2+ oscillations and the normal growth of root hairs. CNGC6, CNGC9 and CNGC14 were expressed in root hairs, with CNGC9 displaying the highest root hair specificity. In individual channel mutants, morphological defects including root hair swelling and branching, as well as bursting, were observed. The developmental phenotypes were amplified in the three cngc double mutant combinations. Finally, cngc6/9/14 triple mutants only developed bulging trichoblasts and could not form normal root hair protrusions because they burst after the transition to the rapid growth phase. Prior to developmental defects, single and double mutants showed increasingly disturbed patterns of Ca2+ oscillations. We conclude that CNGC6, CNGC9 and CNGC14 fulfill partially but not fully redundant functions in generating and maintaining tip-focused Ca2+ oscillations, which are fundamental for proper root hair growth and polarity. Furthermore, the results suggest that these calmodulin-binding and Ca2+ -permeable channels organize a robust tip-focused oscillatory calcium gradient, which is not essential for root hair initiation but is required to control the integrity of the root hair after the transition to the rapid growth phase. Our findings also show that root hairs possess a large ability to compensate calcium-signaling defects, and add new players to the regulatory network, which coordinates cell wall properties and cell expansion during polar root hair growth.
TL;DR: It is found that AHA2 drives root cell expansion during growth but that, unexpectedly, restriction of root hair elongation is dependent on AHA1 and AHA7, with each having different roles in this process.
Abstract: Plasma membrane H+ -ATPase pumps build up the electrochemical H+ gradients that energize most other transport processes into and out of plant cells through channel proteins and secondary active carriers In Arabidopsis thaliana, the AUTOINHIBITED PLASMA MEMBRANE H+ -ATPases AHA1, AHA2 and AHA7 are predominant in root epidermal cells In contrast to other H+ -ATPases, we find that AHA7 is autoinhibited by a sequence present in the extracellular loop between transmembrane segments 7 and 8 Autoinhibition of pump activity was regulated by extracellular pH, suggesting negative feedback regulation of AHA7 during establishment of an H+ gradient Due to genetic redundancy, it has proven difficult to test the role of AHA2 and AHA7, and mutant phenotypes have previously only been observed under nutrient stress conditions Here, we investigated root and root hair growth under normal conditions in single and double mutants of AHA2 and AHA7 We find that AHA2 drives root cell expansion during growth but that, unexpectedly, restriction of root hair elongation is dependent on AHA2 and AHA7, with each having different roles in this process
TL;DR: The results confirm the importance of root hairs for maize P uptake and content, but not for internal P concentrations, and suggest that the performance of root hair mutants may be biased by secondary effects, such as altered root growth.
TL;DR: A critical role is demonstrated in auxin-mediated root development in Arabidopsis, in which PLC2 influences the polar distribution of PIN2 and the PIN2 polarity and cycling in plc2 root epidermis cells were altered.
Abstract: Nine phosphatidylinositol-specific phospholipases C (PLCs) have been identified in the Arabidopsis genome; among the importance of PLC2 in reproductive development is significant. However, the role of PLC2 in vegetative development such as in root growth is elusive. Here, we report that plc2 mutants displayed multiple auxin-defective phenotypes in root development, including short primary root, impaired root gravitropism, and inhibited root hair growth. The DR5:GUS expression and the endogenous indole-3-acetic acid (IAA) content, as well as the responses of a set of auxin-related genes to exogenous IAA treatment, were all decreased in plc2 seedlings, suggesting the influence of PLC2 on auxin accumulation and signalling. The root elongation of plc2 mutants was less sensitive to the high concentration of exogenous auxins, and the application of 1-naphthaleneacetic acid or the auxin transport inhibitor N-1-naphthylphthalamic acid could rescue the root hair growth of plc2 mutants. In addition, the PIN2 polarity and cycling in plc2 root epidermis cells were altered. These results demonstrate a critical role of PLC2 in auxin-mediated root development in Arabidopsis, in which PLC2 influences the polar distribution of PIN2.
TL;DR: This work aims to analyze the root system architecture and morphology of wheat genotypes to explain their variation in PUE, with findings that a greater CHA and RHD in RAC875 were likely to contribute to improved P uptake, resulting in its higher shoot biomass and grain yield.
Abstract: Variation in root system architecture (RSA) and morphology are important for improving phosphorus use efficiency (PUE) in wheat. This work aims to analyze the root system architecture and morphology of wheat genotypes to explain their variation in PUE. Two genotypes differing in PUE, RAC875 (P efficient) and Wyalkatchem (P inefficient) were grown in a sandy soil amended with adequate basal nutrients and two P rates (10 and 30 mg P kg−1). RSA traits were measured by freely available software, GiA roots and DIRT, and root hair features were measured using a microscope with an attached camera and LAS v3.6 software. Under low P supply, RAC875 produced greater shoot dry matter (DM) at 24, 27 and 48 days after sowing (DAS), and at maturity, RAC875 also had a higher grain yield at maturity. Enhanced P efficiency (biomass and seed yield at inadequate P supply relative to adequate P supply) was observed more so in RAC875 at all harvest times. P supply affected most RSA traits, with low P leading to reductions in convex hull area (CHA), root surface area, root volume, total root length and root tip number. RAC875 produced significantly greater CHA than Wyalkatchem at low P supply while Wyalkatchem had significantly larger CHA than RAC875 when P was non-limiting. RAC875 also had greater root hair density (RHD) than Wyalkatchem at low P level, but no difference was observed at adequate P. When grown under low P supply, a greater CHA and RHD in RAC875 were likely to contribute to improved P uptake, resulting in its higher shoot biomass and grain yield.
TL;DR: It is reported that in Arabidopsis roots, auxin elicits specific Ca2+ signaling patterns that spatially coincide with the expression pattern of auxin-regulated genes that can function in a cell-specific fashion at steady-state as well as at elevated cellular Ca 2+ levels to regulate auxin responses.
Abstract: Signaling cross talks between auxin, a regulator of plant development, and Ca2+, a universal second messenger, have been proposed to modulate developmental plasticity in plants. However, the underlying molecular mechanisms are largely unknown. Here, we report that in Arabidopsis roots, auxin elicits specific Ca2+ signaling patterns that spatially coincide with the expression pattern of auxin-regulated genes. We have identified the single EF-hand Ca2+-binding protein Ca2+-dependent modulator of ICR1 (CMI1) as an interactor of the Rho of plants (ROP) effector interactor of constitutively active ROP (ICR1). CMI1 expression is directly up-regulated by auxin, whereas the loss of function of CMI1 associates with the repression of auxin-induced Ca2+ increases in the lateral root cap and vasculature, indicating that CMI1 represses early auxin responses. In agreement, cmi1 mutants display an increased auxin response including shorter primary roots, longer root hairs, longer hypocotyls, and altered lateral root formation. Binding to ICR1 affects subcellular localization of CMI1 and its function. The interaction between CMI1 and ICR1 is Ca2+-dependent and involves a conserved hydrophobic pocket in CMI1 and calmodulin binding-like domain in ICR1. Remarkably, CMI1 is monomeric in solution and in vitro changes its secondary structure at cellular resting Ca2+ concentrations ranging between 10−9 and 10−8 M. Hence, CMI1 is a Ca2+-dependent transducer of auxin-regulated gene expression, which can function in a cell-specific fashion at steady-state as well as at elevated cellular Ca2+ levels to regulate auxin responses.
TL;DR: Interfering with leucine biosynthesis affects the TOR network and causes changes in cell growth that lead to suppression of the cell wall formation mutant lrx1.
Abstract: The growth and development of organisms must be tightly controlled and adjusted to nutrient availability and metabolic activities. The Target of Rapamycin (TOR) network is a major control mechanism in eukaryotes and influences processes such as translation, mitochondrial activity, production of reactive oxygen species, and the cytoskeleton. In Arabidopsis thaliana, inhibition of the TOR kinase causes changes in cell wall architecture and suppression of phenotypic defects of the cell wall formation mutant lrx1 (leucine-rich repeat extensin 1). The rol17 (repressor of lrx1 17) mutant was identified as a new suppressor of lrx1 that induces also a short root phenotype. The ROL17 locus encodes isopropylmalate synthase 1, a protein involved in leucine biosynthesis. Dependent on growth conditions, mutations in ROL17 do not necessarily alter the level of leucine, but always cause development of the rol17 mutant phenotypes, suggesting that the mutation does not only influence leucine biosynthesis. Changes in the metabolome of rol17 mutants are also found in plants with inhibited TOR kinase activity. Furthermore, rol17 mutants show reduced sensitivity to the TOR kinase inhibitor AZD-8055, indicating a modified TOR network. Together, these data suggest that suppression of lrx1 by rol17 is the result of an alteration of the TOR network.
TL;DR: The results suggest the activation of cell-division-related mechanisms by AM hosts during the accommodation of the symbiotic fungus.
Abstract: Arbuscular mycorrhizas (AMs) between plants and soil fungi are widespread symbioses with a major role in soil nutrient uptake. In this study we investigated the induction of root cortical cell division during AM colonization by combining morphometric and gene expression analyses with promoter activation and protein localization studies of the cell-plate-associated exocytic marker TPLATE. Our results show that TPLATE promoter is activated in colonized cells of the root cortex where we also observed the appearance of cells that are half the size of the surrounding cells. Furthermore, TPLATE-green fluorescent protein recruitment to developing cell plates highlighted ectopic cell division events in the inner root cortex during early AM colonization. Lastly, transcripts of TPLATE, KNOLLE and Cyclinlike 1 (CYC1) are all upregulated in the same context, alongside endocytic markers Adaptor-Related Protein complex 2 alpha 1 subunit (AP2A1) and Clathrin Heavy Chain 2 (CHC2), known to be active during cell plate formation. This pattern of gene expression was recorded in wild-type Medicago truncatula roots, but not in a common symbiotic signalling pathway mutant where fungal colonization is blocked at the epidermal level. Altogether, these results suggest the activation of cell-division-related mechanisms by AM hosts during the accommodation of the symbiotic fungus.
TL;DR: YPT-interacting proteins 4a and 4b (YIP4a/b) contribute to activation and plasma membrane accumulation of Rho-of-plant (ROP) small GTPases during hair initiation, identifying YIP4 a/b as central trafficking components in ROP-dependent root hair formation.
Abstract: Root hairs are protrusions from root epidermal cells with crucial roles in plant soil interactions. Although much is known about patterning, polarity and tip growth of root hairs, contributions of membrane trafficking to hair initiation remain poorly understood. Here, we demonstrate that the trans-Golgi network-localized YPT-INTERACTING PROTEIN 4a and YPT-INTERACTING PROTEIN 4b (YIP4a/b) contribute to activation and plasma membrane accumulation of Rho-of-plant (ROP) small GTPases during hair initiation, identifying YIP4a/b as central trafficking components in ROP-dependent root hair formation.