Showing papers in "New Phytologist in 2022"

Plant-microbiome interactions under a changing world: responses, consequences, and perspective.

Abstract: Climate change is increasing global temperatures and the frequency and severity of droughts in many regions. These anthropogenic stresses pose a significant threat to plant performance and crop production. The plant-associated microbiome modulates the impacts of biotic and abiotic stresses on plant fitness. However, climate change induced change in composition and activities of plant microbiomes, can affect host functions. Here, we highlight recent advancements in our understanding of the impact of climate change (warming and drought) on plant-microbiome interactions and on their ecological functions from genome to ecosystem scales. We identify knowledge gaps, propose new concepts, and make recommendations for future research directions. It is proposed that in short-term (years to decades) adaptation of plants to climate change is mainly driven by the plant microbiome, while long-term (century to millennia) adaptation of plants will be driven equally by eco-evolutionary interactions between the plant microbiome and its host. A better understanding of the response of plant and its microbiome interactions to climate change and the ways in which microbiomes can mitigate the negative impacts will better inform predictions of climate change impacts on primary productivity and aid in developing management and policy tools to improve the resilience of plant systems.

Plant responses to multifactorial stress combination.

Abstract: Human activity is causing a global change in plant environment that includes a significant increase in the number and intensity of different stress factors. These include combinations of multiple abiotic and biotic stressors that simultaneously or sequentially impact plants and microbiomes causing a significant decrease in plant growth, yield, and overall health. It was recently found that with the increasing number and complexity of stressors simultaneously impacting a plant, plant growth and survival dramatically declines, even if the level of each individual stress, involved in such 'multifactorial stress combination', is low enough to not have a significant effect. Here we highlight this new concept of multifactorial stress combination and discuss its importance for our efforts to develop climate change-resilient crops.

On the expansion of biological functions of lytic polysaccharide monooxygenases

Abstract: Lytic polysaccharide monooxygenases (LPMOs) constitute an enigmatic class of enzymes, the discovery of which has opened up a new arena of riveting research. LPMOs can oxidatively cleave the glycosidic bonds found in carbohydrate polymers enabling the depolymerisation of recalcitrant biomasses, such as cellulose or chitin. While most studies have so far mainly explored the role of LPMOs in a (plant) biomass conversion context, alternative roles and paradigms begin to emerge. In the present review, we propose a historical perspective of LPMO research providing a succinct overview of the major achievements of LPMO research over the past decade. This journey through LPMOs landscape leads us to dive into the emerging biological functions of LPMOs and LPMO-like proteins. We notably highlight roles in fungal and oomycete plant pathogenesis (e.g. potato late blight), but also in mutualistic/commensalism symbiosis (e.g. ectomycorrhizae). We further present the potential importance of LPMOs in other microbial pathogenesis including diseases caused by bacteria (e.g. pneumonia), fungi (e.g. human meningitis), oomycetes and viruses (e.g. entomopox), as well as in (micro)organism development (including several plant pests). Our assessment of the literature leads to the formulation of outstanding questions, promising for the coming years exciting research and discoveries on these moonlighting proteins.

Deciphering the role of specialist and generalist plant-microbial interactions as drivers of plant-soil feedback.

Abstract: Feedback between plants and soil microbial communities can be a powerful driver of vegetation dynamics. Plants elicit changes in the soil microbiome that either promote or suppress conspecifics at the same location, thereby regulating population density-dependence and species coexistence. Such effects are often attributed to the accumulation of host-specific antagonistic or beneficial microbiota in the rhizosphere. However, the identity and host-specificity of the microbial taxa involved are rarely empirically assessed. Here we review the evidence for host-specificity in plant-associated microbes and propose that specific plant-soil feedbacks can also be driven by generalists. We outline the potential mechanisms by which generalist microbial pathogens, mutualists and decomposers can generate differential effects on plant hosts and synthesise existing evidence to predict these effects as a function of plant investments into defence, microbial mutualists and dispersal. Importantly, the capacity of generalist microbiota to drive plant-soil feedbacks depends not only on the traits of individual plants but also on the phylogenetic and functional diversity of plant communities. Identifying factors that promote specialisation or generalism in plant-microbial interactions and thereby modulate the impact of microbiota on plant performance will advance our understanding of the mechanisms underlying plant-soil feedback and the ways it contributes to plant coexistence.

Species divergence with gene flow and hybrid speciation on the Qinghai-Tibet Plateau.

Abstract: The Qinghai-Tibet Plateau (QTP) sensu lato (sl), comprising the platform, the Himalaya, and the Hengduan Mountains, is characterized by a high number of endemic plant species. This evolutionary cradle may arise from explosive species diversification because of geographic isolation. However, gene flow has been widely detected during the speciation processes of all examined groups, suggesting that natural selection may have also played an important role during species divergences in this region. In addition, natural hybrids have been recovered in almost all species-rich genera. This suggests that numerous species in this region are still 'on the speciation pathway to complete reproductive isolation (RI)'. Such hybrids could directly develop into new species through hybrid polyploidization and homoploid hybrid speciation (HHS). HHS may take place more easily than previously thought through alternate inheritance of alleles of parents at multiple RI loci. Therefore, isolation, selection and hybridization could have together promoted species diversification of numerous plant genera on the QTP sl. We emphasize the need for identification and functional analysis of alleles of major genes for speciation, and especially encourage investigations of parallel adaptive divergence causing RI across different lineages within similar but specific habitats in this region.

Epigenetic regulation of thermomorphogenesis and heat stress tolerance.

Abstract: Many environmental conditions fluctuate and organisms need to respond effectively. This is especially true for temperature cues that can change in minutes to seasons and often follow a diurnal rhythm. Plants cannot migrate and most cannot regulate their temperature. Therefore, a broad array of responses evolved to deal with temperature cues from freezing to heat stress. A particular response to mildly elevated temperatures is called thermomorphogenesis, a suite of morphological adaptations that includes thermonasty, formation of thin leaves and elongation growth of petioles and hypocotyl. Thermomorphogenesis allows for optimal performance in suboptimal temperature conditions by enhancing cooling capacity. When temperatures rise further, heat stress tolerance mechanisms can be induced that enable the plant to survive the stressful temperature, which typically comprises of cellular protection mechanisms and memory thereof. Induction of thermomorphogenesis, heat stress tolerance and stress memory depend on gene expression regulation, governed by diverse epigenetic processes. In this Tansley review we update on the current knowledge of epigenetic regulation of heat stress tolerance and elevated temperature signalling and response, with a focus on thermomorphogenesis regulation and heat stress memory. In particular we highlight the emerging role of H3K4 methylation marks in diverse temperature signalling pathways.

The effects of arbuscular mycorrhizal fungal species and taxonomic groups on stressed and unstressed plants: a global meta-analysis.

Abstract: ●The great majority of plants gain access to soil nutrients and enhance their performance under stressful conditions through symbiosis with arbuscular mycorrhizal fungi (AMF). The benefits that AMF confer vary among species and taxonomic groups. However, a comparative analysis of the different benefits among AMF has not yet been performed. ●We conducted a global meta-analysis of recent studies testing the benefits of individual AMF species and main taxonomic groups in terms of plant performance (growth and nutrition). Separately, we examined AMF benefits to plants facing biotic (pathogens, parasites, and herbivores) and abiotic (drought, salinity, and heavy metals) stress. ●AMF had stronger positive effects on plant growth and phosphorus nutrition than on nitrogen nutrition and the effects on the growth of plants facing biotic and abiotic stresses were similarly positive. While the AMF taxonomic groups showed positive effects on plant performance either with or without stress, Diversisporales were the most beneficial to plants without stress and Gigasporales to plants facing biotic stress. ●Our results provide a comprehensive analysis of the benefits of different AMF species and taxonomic groups on plant performance and useful insights for their management and use as bio-inoculants for agriculture and restoration.

Impacts of global change on the phyllosphere microbiome

Abstract: Plants form complex interaction networks with diverse microbiomes in the environment, and the intricate interplay between plants and their associated microbiomes can greatly influence ecosystem processes and functions. The phyllosphere, the aerial part of the plant, provides a unique habitat for diverse microbes, and in return the phyllosphere microbiome greatly affects plant performance. As an open system, the phyllosphere is subjected to environmental perturbations, including global change, which will impact the crosstalk between plants and their microbiomes. In this review, we aim to provide a synthesis of current knowledge of the complex interactions between plants and the phyllosphere microbiome under global changes and to identify future priority areas of research on this topic.

Embracing mountain microbiome and ecosystem functions under global change.

Abstract: Mountains are pivotal to maintaining habitat heterogeneity, global biodiversity, ecosystem functions and services to humans. They have provided classic model natural systems for plant and animal diversity gradient studies for over 250 years. In the recent decade, exploration of microorganisms on mountainsides has also achieved substantial progresses. Here, we review the literature on microbial diversity across taxonomic groups and ecosystem types on global mountains. Microbial community shows climatic zonation with orderly successions along elevational gradients, which are largely consistent with traditional climatic hypotheses. However, elevational patterns are complicated for species richness without general rules in terrestrial and aquatic environments and are driven mainly by deterministic processes caused by abiotic and biotic factors. We see a major shift from documenting patterns of biodiversity towards identifying the mechanisms that shape microbial biogeographical patterns and how these patterns vary under global change by inclusion of novel ecological theories, frameworks and approaches. We thus propose key questions and cutting-edge perspectives to advance future research in mountain microbial biogeography by focusing on biodiversity hypotheses, incorporating meta-ecosystem framework and novel key drivers, adapting recently developed approaches in trait-based ecology and manipulative field experiments, disentangling biodiversity-ecosystem functioning relationships, and finally modelling and predicting their global change responses.

Plant sizes and shapes above and belowground and their interactions with climate

Abstract: Summary Although the above and belowground sizes and shapes of plants strongly influence plant competition, community structure, and plant–environment interactions, plant sizes and shapes remain poorly characterized across climate regimes. We investigated relationships among shoot and root system size and climate. We assembled and analyzed, to our knowledge, the largest global database describing the maximum rooting depth, lateral spread, and shoot size of terrestrial plants – more than doubling the Root Systems of Individual Plants database to 5647 observations. Water availability and growth form greatly influence shoot size, and rooting depth is primarily influenced by temperature seasonality. Shoot size is the strongest predictor of lateral spread, with root system diameter being two times wider than shoot width on average for woody plants. Shoot size covaries strongly with rooting system size; however, the geometries of plants differ considerably across climates, with woody plants in more arid climates having shorter shoots, but deeper, narrower root systems. Additionally, estimates of the depth and lateral spread of plant root systems are likely underestimated at the global scale.

Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes

Abstract: Summary Evergreen species are widespread across the globe, representing two major plant functional forms in terrestrial models. We reviewed and analysed the responses of photosynthesis and respiration to warming in 101 evergreen species from boreal to tropical biomes. Summertime temperatures affected both latitudinal gas exchange rates and the degree of responsiveness to experimental warming. The decrease in net photosynthesis at 25°C (A net25) was larger with warming in tropical climates than cooler ones. Respiration at 25°C (R 25) was reduced by 14% in response to warming across species and biomes. Gymnosperms were more sensitive to greater amounts of warming than broadleaved evergreens, with A net25 and R 25 reduced c. 30–40% with > 10°C warming. While standardised rates of carboxylation (V cmax25) and electron transport (J max25) adjusted to warming, the magnitude of this adjustment was not related to warming amount (range 0.6–16°C). The temperature optimum of photosynthesis (T optA) increased on average 0.34°C per °C warming. The combination of more constrained acclimation of photosynthesis and increasing respiration rates with warming could possibly result in a reduced carbon sink in future warmer climates. The predictable patterns of thermal acclimation across biomes provide a strong basis to improve modelling predictions of the future terrestrial carbon sink with warming.

Seed microbiota revealed by a large-scale meta-analysis including 50 plant species.

Abstract: Seed microbiota constitutes a primary inoculum for plants that is gaining attention due to its role for plant health and productivity. Here, we performed a meta-analysis on 63 seed microbiota studies covering 50 plant species to synthesize knowledge on the diversity of this habitat. Seed microbiota are diverse and extremely variable, with taxa richness varying from one to thousands of taxa. Hence, seed microbiota presents a variable (i.e flexible) microbial fraction but we also identified a stable (i.e. core) fraction across samples. Around 30 bacterial and fungal taxa are present in most plant species and in samples from all over the world. Core taxa, such as Pantoea agglomerans, Pseudomonas viridiflava, P. fluorescens, Cladosporium perangustum and Alternaria sp., are dominant seed taxa. The characterization of the core and flexible seed microbiota provided here will help uncover seed microbiota roles for plant health and design effective microbiome engineering.

Bio-organic soil amendment promotes the suppression of Ralstonia solanacearum by inducing changes in the functionality and composition of rhizosphere bacterial communities.

Abstract: Stimulating the development of soil suppressiveness against certain pathogens represents a sustainable solution toward reducing pesticide use in agriculture. However, understanding the dynamics of suppressiveness and the mechanisms leading to pathogen control remain largely elusive. Here, we investigated the mechanisms used by the rhizosphere microbiome induces bacterial wilt disease suppression in a long-term field experiment where continuous application of bio-organic (BF) fertilizers triggered disease suppressiveness when compared to chemical fertilizer (CF) application. We further demonstrated in a greenhouse experiment that the suppressiveness of the rhizosphere bacterial communities was triggered mainly by changes in community composition rather than only by the abundance of the introduced biocontrol strain. Metagenomics approaches revealed that members of the families Sphingomonadaceae and Xanthomonadaceae with the ability to produce secondary metabolites were enriched in the BF plant rhizosphere but only upon pathogen invasion. We experimentally validated this observation by inoculating bacterial isolates belonging to the families Sphingomonadaceae and Xanthomonadaceae into conducive soil, which led to a significant reduction in pathogen abundance and increase in non-ribosomal peptide synthetase (NRPS) gene abundance. We conclude that priming of the soil microbiome with bio-organic fertilizer amendment fostered reactive bacterial communities in the rhizosphere of tomato plants in response to biotic disturbance.

Routes to roots: direct evidence of water transport by arbuscular mycorrhizal fungi to host plants

Abstract: Arbuscular mycorrhizal fungi (AMF) can help mitigate plant responses to water stress, but it is unclear whether AMF do so by indirect mechanisms, direct water transport to roots, or a combination of the two. Here, we investigated if and how the AMF Rhizophagus intraradices transported water to the host plant Avena barbata, wild oat. We used two-compartment microcosms, isotopically labeled water, and a fluorescent dye to directly track and quantify water transport by AMF across an air gap to host plants. Plants grown with AMF that had access to a physically separated compartment containing 18 O-labeled water transpired almost twice as much as plants with AMF excluded from that compartment. Using an isotopic mixing model, we estimated that water transported by AMF across the air gap accounted for 34.6% of the water transpired by host plants. In addition, a fluorescent dye indicated that hyphae were able to transport some water via an extracytoplasmic pathway. Our study provides direct evidence that AMF can act as extensions of the root system along the soil-plant-air continuum of water movement, with plant transpiration driving water flow along hyphae outside of the hyphal cell membrane.

ARFs are keys to the many auxin doors.

Abstract: In plants, most developmental programs depend on auxin action. The best described model of auxin signaling pathway that explains most, but not all, auxin transcriptional responses relies on a derepression mechanism. Repressors called Aux/IAAs (Auxin/Indole-3-Acetic Acid) interact with ARFs (Auxin Response Factors), the transcription factors of the auxin signaling pathway, leading to a repression of ARF-controlled genes. Auxin induces Aux/IAA degradation, releases ARFs and activates transcription. However, this elegant model is not suitable for all ARFs. Indeed, in Arabidopsis thaliana which has 22 ARFs, only 5 of them fit into the model since they are the ones able to interact with Aux/IAAs. The 17 left have a limited capacity to interact with the repressors and their mechanism is still unclear. ARF-Aux/IAA differential interaction is one of the many examples of ARFs biochemical and structural diversification that affects ARFs action and therefore, auxin transcriptional responses. A deeper understanding of the structural properties of ARFs is fundamental to better explain the action of auxin in plants.

Con‐Ca2+‐tenating plant immune responses via calcium‐permeable cation channels

Abstract: Summary Calcium serves as a second messenger in a variety of developmental and physiological processes and has long been identified as important for plant immune responses. We discuss recent discoveries regarding plant immune‐related calcium‐permeable channels and how the two intertwined branches of the plant immune system are intricately linked to one another through calcium signalling. Cell surface immune receptors carefully tap the immense calcium gradient that exists between apoplast and cytoplasm in a short burst via tightly regulated plasma membrane (PM)‐resident cation channels. Intracellular immune receptors form atypical calcium‐permeable cation channels at the PM and mediate a prolonged calcium influx, overcoming the deleterious influence of pathogen effectors and enhancing plant immune responses.

Evolutionary biology of lichen symbioses.

Abstract: Lichens are the symbiotic outcomes of open, interspecies relationships, central to which are a fungus and a phototroph, typically an alga and/or cyanobacterium. The evolutionary processes that led to the global success of lichens are poorly understood. In this review, we explore the goods and services exchange between fungus and phototroph and how this propelled the success of both symbiont and symbiosis. Lichen fungal symbionts count among the only filamentous fungi that expose most of their mycelium to an aerial environment. Phototrophs export carbohydrates to the fungus, which converts them to specific polyols. Experimental evidence suggests that polyols are not only growth and respiratory substrates but also play a role in anhydrobiosis, the capacity to survive desiccation. We propose that this dual functionality is pivotal to the evolution of fungal symbionts, enabling persistence in environments otherwise hostile to fungi while simultaneously imposing costs on growth. Phototrophs, in turn, benefit from fungal protection from herbivory and light stress, while appearing to exert leverage over fungal sex and morphogenesis. Combined with the recently recognized habit of symbionts to occur in multiple symbioses, this creates the conditions for a multiplayer marketplace of rewards and penalties that could drive symbiont selection and lichen diversification.

The other side of tropical forest drought: do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

Abstract: Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

CsMYB1 integrates the regulation of trichome development and catechins biosynthesis in tea plant domestication

Abstract: Summary Tea trichomes synthesize numerous specialized metabolites to protect plants from environmental stresses and contribute to tea flavours, but little is known about the regulation of trichome development. Here, we showed that CsMYB1 is involved in the regulation of trichome formation and galloylated cis‐catechins biosynthesis in tea plants. The variations in CsMYB1 expression levels are closely correlated with trichome indexes and galloylated cis‐catechins contents in tea plant populations. Genome resequencing showed that CsMYB1 may be selected in modern tea cultivars, since a 192‐bp insertion in CsMYB1 promoter was found exclusively in modern tea cultivars but not in the glabrous wild tea Camellia taliensis. Several enhancers in the 192‐bp insertion increased CsMYB1 transcription in modern tea cultivars that coincided with their higher galloylated cis‐catechins contents and trichome indexes. Biochemical analyses and transgenic data showed that CsMYB1 interacted with CsGL3 and CsWD40 and formed a MYB‐bHLH‐WD40 (MBW) transcriptional complex to activate the trichome regulator genes CsGL2 and CsCPC, and the galloylated cis‐catechins biosynthesis genes anthocyanidin reductase and serine carboxypeptidase‐like 1A. CsMYB1 integratively regulated trichome formation and galloylated cis‐catechins biosynthesis. Results suggest that CsMYB1, trichome and galloylated cis‐catechins are coincidently selected during tea domestication by harsh environments for improved adaption and by breeders for better tea flavours.

Plant phosphorus-use and -acquisition strategies in Amazonia.

Abstract: In the tropical rainforest of Amazonia, phosphorus (P) is one of the main nutrients controlling forest dynamics, but its effects on the future of the forest biomass carbon (C) storage under elevated atmospheric CO2 concentrations remain uncertain. Soils in vast areas of Amazonia are P impoverished, and little is known about the variation or plasticity in plant P-use and -acquisition strategies across space and time, hampering the accuracy of projections in vegetation models. Here, we synthesize the current knowledge of leaf P resorption, fine-root P foraging, arbuscular mycorrhizal symbioses, and root acid phosphatase and organic acid exudation and discuss how these strategies vary with soil P concentrations and in response to elevated atmospheric CO2 . We identify knowledge gaps and suggest ways forward to fill those gaps. Additionally, we propose a conceptual framework for the variations in plant P-use and -acquisition strategies along soil P gradients of Amazonia. We suggest that in soils with intermediate to high P concentrations, at the plant community level, investments are primarily directed to P foraging strategies via roots and arbuscular mycorrhizas, whereas, in soils with intermediate to low P concentrations, investments shift to prioritize leaf P resorption and mining strategies via phosphatases and organic acids.

Heatwave breaks down the linearity between sun‐induced fluorescence and gross primary production

Abstract: Sun-induced fluorescence in the far-red region (SIF) is increasingly used as a remote and proximal-sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves. Here, we examined how the 2018 European heatwave (HW) affected the GPP-SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy-scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence. The HW caused an inversion of the photosynthesis-fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF. Our results show the complex modulation of the NPQ-SIF-GPP relationship at an extreme level of heat stress, which is not completely represented in state-of-the-art coupled radiative transfer and photosynthesis models.

Genetic variation in <i>YIGE1</i> contributes to ear length and grain yield in maize

Abstract: Ear length (EL), which is controlled by quantitative trait loci (QTLs), is an important component of grain yield and as such is a key target trait in maize breeding. However, very few EL QTLs have been cloned, and their molecular mechanisms are largely unknown. Here, using a genome wide association study (GWAS), we identified a QTL, YIGE1, which encodes an unknown protein that regulates EL by affecting pistillate floret number. Overexpression of YIGE1 increased female inflorescence meristem (IM) size, increased EL and kernel number per row (KNPR), and thus enhanced grain yield. By contrast, CRISPR/Cas9 knockout and Mutator insertion mutant lines of YIGE1 displayed decreased IM size and EL. A single-nucleotide polymorphism (SNP) located in the regulatory region of YIGE1 had a large effect on its promoter strength, which positively affected EL by increasing gene expression. Further analysis shows that YIGE1 may be involved in sugar and auxin signal pathways to regulate maize ear development, thus affecting IM activity and floret production in maize inflorescence morphogenesis. These findings provide new insights into ear development and will ultimately facilitate maize molecular breeding.

SlWRKY35 positively regulates carotenoid biosynthesis by activating the MEP pathway in tomato fruit

Abstract: Carotenoids are vital phytonutrients widely recognised for their health benefits. Therefore, it is vital to thoroughly investigate the metabolic regulatory network underlying carotenoid biosynthesis and accumulation to open new leads towards improving their contents in vegetables and crops. The outcome of our study defines SlWRKY35 as a positive regulator of carotenoid biosynthesis in tomato. SlWRKY35 can directly activate the expression of the 1-deoxy-d-xylulose 5-phosphate synthase (SlDXS1) gene to reprogramme metabolism towards the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway, leading to enhanced carotenoid accumulation. We also show that the master regulator SlRIN directly regulates the expression of SlWRKY35 during tomato fruit ripening. Compared with the SlLCYE overexpression lines, coexpression of SlWRKY35 and SlLCYE can further enhance lutein production in transgenic tomato fruit, indicating that SlWRKY35 represents a potential target towards designing innovative metabolic engineering strategies for carotenoid derivatives. In addition to providing new insights into the metabolic regulatory network associated with tomato fruit ripening, our data define a new tool for improving fruit content in specific carotenoid compounds.

The classical SOS pathway confers natural variation of salt tolerance in maize.

Abstract: Sodium (Na+ ) is the major cation damaging crops in the salinized farmland. Previous studies have shown that the Salt Overly Sensitive (SOS) pathway is important for salt tolerance in Arabidopsis. Nevertheless, the SOS pathway remains poorly investigated in most crops. This study addresses the function of SOS pathway and its association with the natural variation of salt tolerance in maize. Firstly, we show that a naturally occurred 4-bp frame-shifting deletion in ZmSOS1 causes the salt hypersensitive phenotype of the maize inbred line LH65. Accordingly, mutants lacking ZmSOS1 also display a salt hypersensitive phenotype, due to an impaired root-to-rhizosphere Na+ efflux and an increased shoot-Na+ concentration. We next show that the maize SOS3/SOS2 complex (ZmCBL4&ZmCBL8/ZmCIPK24a) phosphorylates ZmSOS1 thus activating its Na+ -transporting activity, with their loss-of-function mutants display salt hypersensitive phenotypes. Moreover, we observe that a LTR/Gypsy insertion decreases the expression of ZmCBL8, thereby increasing shoot-Na+ concentration in natural maize population. Taken together, our study has demonstrated that the maize SOS pathway confers a conservative salt-tolerant role, and the components of SOS pathway (ZmSOS1 and ZmCBL8) confer the natural variations of Na+ regulation and salt tolerance in maize, hence providing important gene targets for breeding salt-tolerant maize.

MdMTA-mediated m6 A modification enhances drought tolerance by promoting mRNA stability and translation efficiency of genes involved in lignin deposition and oxidative stress.

Abstract: Although N6 -methyladenosine (m6 A) modification is the most prevalent RNA modification in eukaryotes, the global m6 A modification landscape and its molecular regulatory mechanism in response to drought stress remain unclear. Transcriptome-wide m6 A methylome revealed that m6 A is mainly enriched in the coding sequence (CDS) and 3' untranslated region (UTR), regions in response to drought stress in apple, by recognizing the plant-specific sequence motif UGUAH (M=A, U or C). We identified a catalytic active component of the m6 A methyltransferase complex, MdMTA. In vitro methyl transfer assay, dot blot, LC-MS/MS, and m6 A-seq suggested that MdMTA is a m6 A writer and essential for m6 A mRNA modification. Further studies revealed that MdMTA is required for apple drought tolerance. m6 A-seq and RNA-seq analyses under drought conditions showed that MdMTA mediates m6 A modification and transcripts of mRNAs involved in oxidative stress and lignin deposition. Moreover, m6 A modification promotes mRNA stability and the translation efficiency of these genes in response to drought stress. Consistently, MdMTA enhances lignin deposition and reactive oxygen species (ROS) scavenging under drought conditions. Our results reveal the global involvement of m6 A modification in the drought response of perennial apple trees and illustrate its molecular mechanisms, thereby providing candidate genes for the breeding of stress-tolerant apple cultivars.

Mycorrhizal symbiosis pathway and edaphic fertility frame root economics space among tree species.

Abstract: The root economics space (RES) is multidimensional and largely shaped by belowground biotic and abiotic influences. However, how root-fungal symbioses and edaphic fertility drive this complexity remains unclear. Here, we measured absorptive root traits of 112 tree species in temperate and subtropical forests of China, including traits linked to functional differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) hosts. Our data, from known mycorrhizal tree species, revealed a 'fungal-symbiosis' dimension distinguishing AM from ECM species. This divergence likely resulted from the contrasting mycorrhizal evolutionary development of AM versus ECM associations. Increased root tissue cortical space facilitates AM symbiosis, whereas increased root branching favors ECM symbiosis. Irrespective of mycorrhizal type, a 'root-lifespan' dimension reflecting aspects of root construction cost and defense was controlled by variation in specific root length and root tissue density, which was fully independent of root nitrogen content. Within this function-based RES, we observed a substantial covariation of axes with soil phosphorus and nitrate levels, highlighting the role played by these two axes in nutrient acquisition and conservation. Overall, our findings demonstrate the importance of evolved mycorrhizal symbiosis pathway and edaphic fertility in framing the RES, and provide theoretical and mechanistic insights into the complexity of root economics.

Functional xylem characteristics associated with drought-induced embolism in angiosperms.

Abstract: Hydraulic failure resulting from drought-induced embolism in the xylem of plants is a key determinant of reduced productivity and mortality. Methods to assess this vulnerability are difficult to achieve at scale, leading to alternative metrics and correlations with more easily measured traits. Such efforts have led to the longstanding and pervasive assumed mechanistic link between vessel diameter and vulnerability in angiosperms. However, there are at least two problems with these assumptions that require critical re-evaluation: (1) our current understanding of drought-induced embolism does not provide a mechanistic explanation for why increased vessel width should lead to greater vulnerability, and (2) the most recent advancements in nano-scale embolism processes suggest that vessel diameter is not a direct driver. Here, we review data from physiological and comparative wood anatomy studies, highlighting the potential anatomical and physico-chemical drivers of embolism formation and spread. We then put forward key knowledge gaps, emphasising what is known, unknown, and speculation. A meaningful evaluation of the diameter-vulnerability link will require a better mechanistic understanding of the biophysical processes at the nano-scale level that determine embolism formation and spread, which will in turn lead to more accurate predictions of how water transport in plants is affected by drought.

Contribution of soil algae to the global carbon cycle.

Abstract: Soil photoautotrophic prokaryotes and micro-eukaryotes - known as soil algae - are, together with heterotrophic microorganisms, a constitutive part of the microbiome in surface soils. Similar to plants, they fix atmospheric carbon (C) through photosynthesis for their own growth, yet their contribution to global and regional biogeochemical C cycling still remains quantitatively elusive. Here, we compiled an extensive dataset on soil algae to generate a better understanding of their distribution across biomes and predict their productivity at a global scale by means of machine learning modelling. We found that, on average, (5.5 ± 3.4) × 106 algae inhabit each gram of surface soil. Soil algal abundance especially peaked in acidic, moist and vegetated soils. We estimate that, globally, soil algae take up around 3.6 Pg C per year, which corresponds to c. 6% of the net primary production of terrestrial vegetation. We demonstrate that the C fixed by soil algae is crucial to the global C cycle and should be integrated into land-based efforts to mitigate C emissions.

The red-flesh of kiwifruit is differentially controlled by specific activation-repression systems.

Abstract: Anthocyanins are visual cues for pollination and seed dispersal. They also impart valuable benefits to consumers of fruit. In kiwifruit (Actinidia spp.) studies have shown at least two MYB activators of anthocyanin, while their real function in fruit and mechanisms are not fully understood. Here, transcriptome and small RNA high-throughput sequencing were performed to comprehensively identify contributors to anthocyanin in kiwifruit. Vines stably over-expression showed that both 35S::MYB10 or MYB110 could up-regulate anthocyanin biosynthesis in fruit of A. chinensis, while MYB10 resulted in anthocyanin accumulation limited to the inner pericarp, which suggests repressive mechanisms underlie anthocyanin biosynthesis in this species. Furthermore, motifs in the C-terminal of MYB10/110 were shown to be responsible for the strength of activation of the anthocyanic response. Transient assays showed that both MYB10 and MYB110 were not directly cleaved by miRNAs, but that miR828 and its phased small RNA AcTAS4-D4(-) efficiently targeted MYB110. Other miRNAs were identified, which were differentially expressed between inner and outer pericarp and showed cleavage of SPL13, ARF16, SCL6 and F-box1 which are repressors of MYB10. We conclude that it is the differential expression and subsequent repression of MYB activators that is responsible for variation in anthocyanin accumulation in kiwifruit species.

The making of suberin

Abstract: Summary Outer protective barriers of animals use a variety of bio‐polymers, based on either proteins (e.g. collagens), or modified sugars (e.g. chitin). Plants, however, have come up with a particular solution, based on the polymerisation of lipid‐like precursors, giving rise to cutin and suberin. Suberin is a structural lipophilic polyester of fatty acids, glycerol and some aromatics found in cell walls of phellem, endodermis, exodermis, wound tissues, abscission zones, bundle sheath and other tissues. It deposits as a hydrophobic layer between the (ligno)cellulosic primary cell wall and plasma membrane. Suberin is highly protective against biotic and abiotic stresses, shows great developmental plasticity and its chemically recalcitrant nature might assist the sequestration of atmospheric carbon by plants. The aim of this review is to integrate the rapidly accelerating genetic and cell biological discoveries of recent years with the important chemical and structural contributions obtained from very diverse organisms and tissue layers. We critically discuss the order and localisation of the enzymatic machinery synthesising the presumed substrates for export and apoplastic polymerisation. We attempt to explain observed suberin linkages by diverse enzyme activities and discuss the spatiotemporal relationship of suberin with lignin and ferulates, necessary to produce a functional suberised cell wall.