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Showing papers in "Plant Physiology in 2011"


Journal ArticleDOI
TL;DR: The discovery that there is a close relationship between ascorbate and glutathione dates from soon after the characterization of the chemical formulae of the two molecules.
Abstract: The discovery that there is a close relationship between ascorbate and glutathione dates from soon after the characterization of the chemical formulae of the two molecules ([Szent-Gyorgyi, 1931][1]; [Hopkins and Morgan, 1936][2]). Similarly, it has long been known that thylakoids can generate

1,929 citations


Journal ArticleDOI
TL;DR: With increasing demand of agricultural production and as the peak in global production will occur in the next decades, phosphorus (P) is receiving more attention as a nonrenewable resource.
Abstract: With increasing demand of agricultural production and as the peak in global production will occur in the next decades, phosphorus (P) is receiving more attention as a nonrenewable resource ([Cordell et al., 2009][1]; [Gilbert, 2009][2]). One unique characteristic of P is its low availability due to

1,144 citations


Journal ArticleDOI
TL;DR: In this paper, the microbial contribution to plant P nutrition and opportunities for manipulating specific microorganisms to enhance P availability in soil has been discussed, as well as the potential for manipulating microorganisms in order to enhance plant P availability.
Abstract: Microorganisms are integral to the soil phosphorus (P) cycle and as such play an important role in mediating the availability of P to plants. Understanding the microbial contribution to plant P nutrition and opportunities for manipulating specific microorganisms to enhance P availability in soil has

974 citations


Journal ArticleDOI
TL;DR: Photosynthesis is a well-established source of reactive oxygen species (ROS) in plants and an efficient antioxidant network is also essential to minimize ROS production.
Abstract: Photosynthesis is a well-established source of reactive oxygen species (ROS) in plants. The photosynthetic electron transport chain (PET) operates in an aerobic environment; thus, regulatory systems are required to minimize ROS production. Moreover, an efficient antioxidant network is also essential

972 citations


Journal ArticleDOI
TL;DR: Events of regional-scale vegetation mortality appear to be increasing in a variety of biomes throughout the Earth and are frequently associated with increased temperatures, droughts, and often with outbreaks of biotic agents such as insects and pathogens.
Abstract: Events of regional-scale vegetation mortality appear to be increasing in a variety of biomes throughout the Earth and are frequently associated with increased temperatures, droughts, and often (but not always) with outbreaks of biotic agents such as insects and pathogens (for review, see [Allen et

953 citations


Journal ArticleDOI
TL;DR: This finding demonstrates that the direct pathway delivers less P to AM plants than to NM counterparts and implies fungus-to-plant signaling, which helps to explain the persistence of AM symbiosis over evolutionary time, even in plants that apparently show no benefits.
Abstract: Arbuscular mycorrhizal (AM) symbiosis is the most common plant strategy that increases phosphorus (P) acquisition, involving approximately 80% of terrestrial plants The AM fungal symbionts provide a very effective pathway (the AM pathway) for uptake, scavenging P from large soil volumes and overcoming depletion in the rhizosphere that occurs when direct (epidermal) root uptake is faster than replacement from the bulk soil Recent physiological and molecular research has shown that the AM pathway makes very large contributions to total plant P even in plants that show no growth increases when AM, compared with non-mycorrhizal (NM) counterparts The AM contribution remains "hidden" unless radioactive tracers are used to track delivery via the AM pathway Importantly, this finding demonstrates that the direct pathway delivers less P to AM plants than to NM counterparts and implies fungus-to-plant signaling The mechanisms by which direct uptake is reduced are unknown, but the hidden contribution of AM uptake means that AM fungi cannot be regarded as parasites, because there is mutualistic exchange of P for organic C regardless of plant growth responses Furthermore, the dominance of the AM pathway helps to explain the persistence of AM symbiosis over evolutionary time, even in plants that apparently show no benefits

925 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied metabolic networks and the reactions of organisms to various external conditions and showed that metabolic networks are a major tool for studying the metabolism of organisms and cells, and through this approach much has been learned about metabolic networks.
Abstract: Over the past decade, metabolomics has developed into a major tool for studying the metabolism of organisms and cells, and through this approach much has been learned about metabolic networks and the reactions of organisms to various external conditions ([Lay et al., 2006][1]). Most of this work

801 citations


Journal ArticleDOI
TL;DR: Phosphorus availability is declining in many systems because of soil, and plant growth in the vast majority of terrestrial ecosystems is limited by low phosphorus availability.
Abstract: Plant growth in the vast majority of terrestrial ecosystems is limited by low phosphorus availability. Over 70% of all terrestrial biomass occurs in low-phosphorus soils, including over half of agricultural land ([Fig. 1][1]). Phosphorus availability is declining in many systems because of soil

789 citations


Journal ArticleDOI
Hai-feng Jia1, Ye-mao Chai1, Chun-Li Li1, Dong Lu1, Jing-Jing Luo1, Ling Qin1, Yuan-Yue Shen1 
TL;DR: It is shown that exogenous sugars, particularly sucrose, can significantly promote ripening while stimulating ABA accumulation and that the putative ABA receptor, FaCHLH/ABAR, is a positive regulator of ripening in response to ABA.
Abstract: The plant hormone abscisic acid (ABA) has been suggested to play a role in fruit development, but supporting genetic evidence has been lacking. Here, we report that ABA promotes strawberry (Fragaria ananassa) fruit ripening. Using a newly established Tobacco rattle virus-induced gene silencing technique in strawberry fruit, the expression of a 9-cis-epoxycarotenoid dioxygenase gene (FaNCED1), which is key to ABA biosynthesis, was down-regulated, resulting in a significant decrease in ABA levels and uncolored fruits. Interestingly, a similar uncolored phenotype was observed in the transgenic RNA interference (RNAi) fruits, in which the expression of a putative ABA receptor gene encoding the magnesium chelatase H subunit (FaCHLH/ABAR) was down-regulated by virus-induced gene silencing. More importantly, the uncolored phenotype of the FaNCED1-down-regulated RNAi fruits could be rescued by exogenous ABA, but the ABA treatment could not reverse the uncolored phenotype of the FaCHLH/ABAR-down-regulated RNAi fruits. We observed that down-regulation of the FaCHLH/ABAR gene in the RNAi fruit altered both ABA levels and sugar content as well as a set of ABA- and/or sugar-responsive genes. Additionally, we showed that exogenous sugars, particularly sucrose, can significantly promote ripening while stimulating ABA accumulation. These data provide evidence that ABA is a signal molecule that promotes strawberry ripening and that the putative ABA receptor, FaCHLH/ABAR, is a positive regulator of ripening in response to ABA.

534 citations


Journal ArticleDOI
TL;DR: It is proposed that the tightly balanced auxin-strigolactone interaction is the basis for the mechanism of the regulation of the plants’ root-to-shoot ratio and that the net result of strigolACTone action is dependent on the auxin status of the plant.
Abstract: In this study, the role of the recently identified class of phytohormones, strigolactones, in shaping root architecture was addressed. Primary root lengths of strigolactone-deficient and -insensitive Arabidopsis (Arabidopsis thaliana) plants were shorter than those of wild-type plants. This was accompanied by a reduction in meristem cell number, which could be rescued by application of the synthetic strigolactone analog GR24 in all genotypes except in the strigolactone-insensitive mutant. Upon GR24 treatment, cells in the transition zone showed a gradual increase in cell length, resulting in a vague transition point and an increase in transition zone size. PIN1/3/7-green fluorescent protein intensities in provascular tissue of the primary root tip were decreased, whereas PIN3-green fluorescent protein intensity in the columella was not affected. During phosphate-sufficient conditions, GR24 application to the roots suppressed lateral root primordial development and lateral root forming potential, leading to a reduction in lateral root density. Moreover, auxin levels in leaf tissue were reduced. When auxin levels were increased by exogenous application of naphthylacetic acid, GR24 application had a stimulatory effect on lateral root development instead. Similarly, under phosphate-limiting conditions, endogenous strigolactones present in wild-type plants stimulated a more rapid outgrowth of lateral root primordia when compared with strigolactone-deficient mutants. These results suggest that strigolactones are able to modulate local auxin levels and that the net result of strigolactone action is dependent on the auxin status of the plant. We postulate that the tightly balanced auxin-strigolactone interaction is the basis for the mechanism of the regulation of the plants’ root-to-shoot ratio.

519 citations


Journal ArticleDOI
TL;DR: Rubisco is a large enzyme with a molecular mass of approximately 550 kD, but its affinity to CO2 is also low, and the K m, K c, at 25°C is low.
Abstract: Rubisco is a large enzyme with a molecular mass of approximately 550 kD. The maximum rate of CO2 fixation (i.e. ribulose-1,5-bisphosphate [RuBP] carboxylation) at CO2 saturation is only 15 to 30 mol CO2 mol−1 Rubisco protein s−1 at 25°C. Affinity to CO2 is also low, and the K m, K c, at 25°C

Journal ArticleDOI
TL;DR: It is demonstrated that the increase in strigolactone production contributes to the changes in shoot architecture observed in response to phosphate deficiency, and that xylem-transported strIGolactones contribute to the regulation of shoot architectural response to phosphorous-limiting conditions.
Abstract: The biosynthesis of the recently identified novel class of plant hormones, strigolactones, is up-regulated upon phosphate deficiency in many plant species. It is generally accepted that the evolutionary origin of strigolactone up-regulation is their function as a rhizosphere signal that stimulates hyphal branching of arbuscular mycorrhizal fungi. In this work, we demonstrate that this induction is conserved in Arabidopsis (Arabidopsis thaliana), although Arabidopsis is not a host for arbuscular mycorrhizal fungi. We demonstrate that the increase in strigolactone production contributes to the changes in shoot architecture observed in response to phosphate deficiency. Using high-performance liquid chromatography, column chromatography, and multiple reaction monitoring-liquid chromatography-tandem mass spectrometry analysis, we identified two strigolactones (orobanchol and orobanchyl acetate) in Arabidopsis and have evidence of the presence of a third (5-deoxystrigol). We show that at least one of them (orobanchol) is strongly reduced in the putative strigolactone biosynthetic mutants more axillary growth1 (max1) and max4 but not in the signal transduction mutant max2. Orobanchol was also detected in xylem sap and up-regulated under phosphate deficiency, which is consistent with the idea that root-derived strigolactones are transported to the shoot, where they regulate branching. Moreover, two additional putative strigolactone-like compounds were detected in xylem sap, one of which was not detected in root exudates. Together, these results show that xylem-transported strigolactones contribute to the regulation of shoot architectural response to phosphate-limiting conditions.

Journal ArticleDOI
TL;DR: Orthophosphate is an essential macronutrient that plays a central role in virtually all major metabolic processes in plants, particularly photosynthesis and respiration.
Abstract: Orthophosphate (Pi) is an essential macronutrient that plays a central role in virtually all major metabolic processes in plants, particularly photosynthesis and respiration. Many metabolites are Pi monoesters, whereas the phosphoanhydride bonds of compounds such as ATP function to transfer energy

Journal ArticleDOI
TL;DR: Light is of course essential for photosynthesis and supports most life on earth, however, light intensity and spectral quality are highly variable in space and time according to time of day, season, geography, climate, and the position of leaf within canopy and cell within leaf.
Abstract: Light is of course essential for photosynthesis and supports most life on earth. However, light intensity and spectral quality are highly variable in space and time according to time of day, season, geography, climate, and the position of leaf within canopy and cell within leaf. This has resulted in

Journal ArticleDOI
TL;DR: Current proposals to improve photosynthesis to meet the authors' energy and food needs include improving the performance of Rubisco and decreasing photorespiration by turning C3 plants into C4 plants, installing algal or cyanobacterial carbon-concentrating mechanisms into higher plant.
Abstract: Current proposals to improve photosynthesis to meet our energy and food needs include the following: (1) improving the performance of Rubisco; (2) decreasing photorespiration by turning C3 plants into C4 plants, installing algal or cyanobacterial carbon-concentrating mechanisms into higher plant

Journal ArticleDOI
TL;DR: A novel, semiautomated image-analysis software to streamline the quantitative analysis of root growth and architecture of complex root systems, which combines a vectorial representation of root objects with a powerful tracing algorithm that accommodates a wide range of image sources and quality.
Abstract: We present in this paper a novel, semi-automated image analysis software to streamline the quantitative analysis of root growth and architecture of complex root systems. The software combines a vectorial representation of root objects with a powerful tracing algorithm which accommodates a wide range of image sources and quality. The root system is treated as a collection of roots (possibly connected) that are individually represented as parsimonious sets of connected segments. Pixel coordinates and grey level are therefore turned into intuitive biological attributes such as segment diameter and orientation, distance to any other segment or topological position. As a consequence, user interaction and data analysis directly operate on biologicalentities (roots) and are not hampered by the spatially discrete, pixel-based nature of the original image. The software supports a sampling-based analysis of root system images, in which detailed information is collected on a limited number of roots selected by the user according to specific research requirements. The use of the software is illustrated with a time-lapse analysis of cluster root formation in lupin (Lupinus albus) and with an architectural analysis of maize root system (Zea mays). The software, SmartRoot, is an operating system independent freeware based on ImageJ and relies on cross-platform standards for communication with data analysis softwares.

Journal ArticleDOI
TL;DR: There is a growing impetus in developing novel strategies to address global concerns regarding food security as crop productivity gains through traditional breeding begin to lag and arable land becomes scarcer.
Abstract: There is a growing impetus in developing novel strategies to address global concerns regarding food security. As crop productivity gains through traditional breeding begin to lag and arable land becomes scarcer, it seems that we are heading for unsustainable global populations. It has been

Journal ArticleDOI
Amane Makino1
TL;DR: Rice ( Oryza sativa ) and wheat ( Triticum aestivum ) are the two most commercially important crops, accounting for more than 40% of global food production.
Abstract: Rice ( Oryza sativa ) and wheat ( Triticum aestivum ) are the two most commercially important crops, accounting for more than 40% of global food production. They were domesticated in different climates and differ largely in their growth environments: Rice is tropically cultivated in hot, wet

Journal ArticleDOI
TL;DR: A novel imaging and software platform was developed for the high-throughput phenotyping of three-dimensional root traits during seedling development and will facilitate novel investigations into the development of entire root systems or selected components of root systems.
Abstract: A novel imaging and software platform was developed for the high-throughput phenotyping of three-dimensional root traits during seedling development. To demonstrate the platform’s capacity, plants of two rice ( Oryza sativa ) genotypes, Azucena and IR64, were grown in a transparent gellan gum system and imaged daily for 10 d. Rotational image sequences consisting of 40 two-dimensional images were captured using an optically corrected digital imaging system. Three-dimensional root reconstructions were generated and analyzed using a custom-designed software, RootReader3D. Using the automated and interactive capabilities of RootReader3D, five rice root types were classified and 27 phenotypic root traits were measured to characterize these two genotypes. Where possible, measurements from the three-dimensional platform were validated and were highly correlated with conventional two-dimensional measurements. When comparing gellan gum-grown plants with those grown under hydroponic and sand culture, significant differences were detected in morphological root traits ( P

Journal ArticleDOI
TL;DR: The characterization of the Arabidopsis ECERIFERUM1 (CER1) gene predicted to encode an enzyme involved in alkane biosynthesis demonstrates that CER1 controls alkanes biosynthesis and is highly linked to responses to biotic and abiotic stresses.
Abstract: Land plant aerial organs are covered by a hydrophobic layer called the cuticle that serves as a waterproof barrier protecting plants against desiccation, ultraviolet radiation, and pathogens. Cuticle consists of a cutin matrix as well as cuticular waxes in which very-long-chain (VLC) alkanes are the major components, representing up to 70% of the total wax content in Arabidopsis (Arabidopsis thaliana) leaves. However, despite its major involvement in cuticle formation, the alkane-forming pathway is still largely unknown. To address this deficiency, we report here the characterization of the Arabidopsis ECERIFERUM1 (CER1) gene predicted to encode an enzyme involved in alkane biosynthesis. Analysis of CER1 expression showed that CER1 is specifically expressed in the epidermis of aerial organs and coexpressed with other genes of the alkane-forming pathway. Modification of CER1 expression in transgenic plants specifically affects VLC alkane biosynthesis: waxes of TDNA insertional mutant alleles are devoid of VLC alkanes and derivatives, whereas CER1 overexpression dramatically increases the production of the odd-carbon-numbered alkanes together with a substantial accumulation of iso-branched alkanes. We also showed that CER1 expression is induced by osmotic stresses and regulated by abscisic acid. Furthermore, CER1-overexpressing plants showed reduced cuticle permeability together with reduced soil water deficit susceptibility. However, CER1 overexpression increased susceptibility to bacterial and fungal pathogens. Taken together, these results demonstrate that CER1 controls alkane biosynthesis and is highly linked to responses to biotic and abiotic stresses.

Journal ArticleDOI
TL;DR: Evidence is provided that RIN interacts with the promoters of genes involved in the major pathways associated with observed and well-studied ripening phenotypes and phenomena, including the transcriptional control network involved in overall ripening regulation, ethylene biosynthesis, Ethylene perception, downstream ethylene response, cell wall metabolism, and carotenoid biosynthesis.
Abstract: Fruit ripening is a complex developmental process responsible for the transformation of the seed-containing organ into a tissue attractive to seed dispersers and agricultural consumers. The coordinated regulation of the different biochemical pathways necessary to achieve this change receives considerable research attention. The MADS-box transcription factor RIPENING INHIBITOR (RIN) is an essential regulator of tomato (Solanum lycopersicum) fruit ripening but the exact mechanism by which it influences the expression of ripening-related genes remains unclear. Using a chromatin immunoprecipitation approach, we provide evidence that RIN interacts with the promoters of genes involved in the major pathways associated with observed and well-studied ripening phenotypes and phenomena, including the transcriptional control network involved in overall ripening regulation, ethylene biosynthesis, ethylene perception, downstream ethylene response, cell wall metabolism, and carotenoid biosynthesis. Furthermore, in the cases of ethylene and carotenoid biosynthesis, RIN interacts with the promoters of genes encoding rate-limiting activities. We also show that RIN recruitment to target loci is dependent on a normally functioning allele at the ripening-specific transcription factor COLORLESS NONRIPENING gene locus, further clarifying the relationship between these two ripening regulators.

Journal ArticleDOI
TL;DR: A genetic network enabling plants to regulate lignin biosynthesis in response to CWD through dynamic interactions between JA and ROS is characterized.
Abstract: The plant cell wall is a dynamic and complex structure whose functional integrity is constantly being monitored and maintained during development and interactions with the environment. In response to cell wall damage (CWD), putatively compensatory responses, such as lignin production, are initiated. In this context, lignin deposition could reinforce the cell wall to maintain functional integrity. Lignin is important for the plant’s response to environmental stress, for reinforcement during secondary cell wall formation, and for long-distance water transport. Here, we identify two stages and several components of a genetic network that regulate CWD-induced lignin production in Arabidopsis (Arabidopsis thaliana). During the early stage, calcium and diphenyleneiodonium-sensitive reactive oxygen species (ROS) production are required to induce a secondary ROS burst and jasmonic acid (JA) accumulation. During the second stage, ROS derived from the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG D and JA-isoleucine generated by JASMONIC ACID RESISTANT1, form a negative feedback loop that can repress each other’s production. This feedback loop in turn seems to influence lignin accumulation. Our results characterize a genetic network enabling plants to regulate lignin biosynthesis in response to CWD through dynamic interactions between JA and ROS.

Journal ArticleDOI
TL;DR: The data suggest that OsPT8 is involved in Pi homeostasis in rice and is critical for plant growth and development.
Abstract: Plant phosphate transporters (PTs) are active in the uptake of inorganic phosphate (Pi) from the soil and its translocation within the plant. Here, we report on the biological properties and physiological roles of OsPht1;8 (OsPT8), one of the PTs belonging to the Pht1 family in rice (Oryza sativa). Expression of a β-glucuronidase and green fluorescent protein reporter gene driven by the OsPT8 promoter showed that OsPT8 is expressed in various tissue organs from roots to seeds independent of Pi supply. OsPT8 was able to complement a yeast Pi-uptake mutant and increase Pi accumulation of Xenopus laevis oocytes when supplied with micromolar 33Pi concentrations at their external solution, indicating that it has a high affinity for Pi transport. Overexpression of OsPT8 resulted in excessive Pi in both roots and shoots and Pi toxic symptoms under the high-Pi supply condition. In contrast, knockdown of OsPT8 by RNA interference decreased Pi uptake and plant growth under both high- and low-Pi conditions. Moreover, OsPT8 suppression resulted in an increase of phosphorus content in the panicle axis and in a decrease of phosphorus content in unfilled grain hulls, accompanied by lower seed-setting rate. Altogether, our data suggest that OsPT8 is involved in Pi homeostasis in rice and is critical for plant growth and development.

Journal ArticleDOI
TL;DR: The relevance of a range of root-induced or microbially-mediated rhizosphere processes driving P acquisition are discussed, and how complementarity may operate when cereals are intercropped with legume by addressing cases of complementary use of soil P resources in space and time.
Abstract: Phosphorus (P) scarcity and the need for ecologically sound intensification of agroecosystems are major challenges we face. To improve nutrient efficiency in agriculture, especially for P, multispecies crop stands may outperform their monospecific counterparts, especially under low input conditions. There is increasing evidence that biomass, grain yield and nutrient acquisition are improved in cereal/legume intercropping systems, relative to cereal or legume grown alone. Hereafter, we consider these observations, outline the underlying mechanisms, and examine recent work that advances our knowledge of how cereal/legume intercropping systems acquire P in their rhizospheres, through various types of positive belowground-interactions. First, we discuss how complementarity may operate when cereals are intercropped with legumes by addressing cases of complementary use of soil P resources in space and time, and showing how functionally diverse intercropped species can use different pools of soil P. Then we address examples of facilitation, i.e. positive interactions between two intercropped species, in which the legume (or cereal) may increase P availability for the benefit of the intercropped cereal (or legume). Finally, the relevance of a range of root-induced or microbially-mediated rhizosphere processes driving P acquisition are discussed.

Journal ArticleDOI
TL;DR: The realization that crop yields are reaching a plateau, while population increases continue at pace, has placed manipulation of photosynthesis in a central position to achieve increases in yield.
Abstract: The realization that crop yields are reaching a plateau, while population increases continue at pace, has placed manipulation of photosynthesis in a central position to achieve increases in yield. Increasing flux through the C3 cycle will be a major focus of this effort. Through application of new

Journal ArticleDOI
TL;DR: This update will focus on phloem loading9s contribution to assimilate partitioning, and its role in balancing photosynthetic activity with sink utilization of photoassimilates.
Abstract: The phloem is a central component of the plant9s complex vascular system that plays a vital role in moving photoassimilates from sites of primary acquisition to the heterotrophic tissues and organs of the plant. Indeed, as much as 50-80% of the CO2 photoassimilated in a mature leaf is transported out of the leaf in the phloem to satisfy the needs of the non-photosynthetic organs of the plant (Kalt-Torres et al., 1987). In recent years, new data has shown that the phloem also plays a key role in moving information molecules that coordinate many facets of plant growth and development (Turgeon and Wolf, 2009). This update will focus on phloem loading9s contribution to assimilate partitioning, and its role in balancing photosynthetic activity with sink utilization of photoassimilates.

Journal ArticleDOI
TL;DR: Hydraulic vulnerability was lower with greater major vein density and smaller leaf size, pointing to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.
Abstract: Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (K(leaf)) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that K(leaf) relates to vein density (vein length per area). Additionally, venation architecture determines the sensitivity of K(leaf) to damage; severing the midrib caused K(leaf) and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces K(leaf), we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for 10 species ranging strongly in drought tolerance, hydraulic vulnerability, determined as the leaf water potential at 50% and 80% loss of K(leaf), was lower with greater major vein density and smaller leaf size (|r| = 0.85-0.90; P < 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.

Journal ArticleDOI
TL;DR: Different functions for MgLysM effector homologs during plant infection are highlighted, including novel activities that distinguish these proteins from C. fulvum Ecp6.
Abstract: Secreted effector proteins enable plant pathogenic fungi to manipulate host defenses for successful infection. Mycosphaerella graminicola causes Septoria tritici blotch disease of wheat (Triticum aestivum) leaves. Leaf infection involves a long (approximately 7 d) period of symptomless intercellular colonization prior to the appearance of necrotic disease lesions. Therefore, M. graminicola is considered as a hemibiotrophic (or necrotrophic) pathogen. Here, we describe the molecular and functional characterization of M. graminicola homologs of Ecp6 (for extracellular protein 6), the Lysin (LysM) domain-containing effector from the biotrophic tomato (Solanum lycopersicum) leaf mold fungus Cladosporium fulvum, which interferes with chitin-triggered immunity in plants. Three LysM effector homologs are present in the M. graminicola genome, referred to as Mg3LysM, Mg1LysM, and MgxLysM. Mg3LysM and Mg1LysM genes were strongly transcriptionally up-regulated specifically during symptomless leaf infection. Both proteins bind chitin; however, only Mg3LysM blocked the elicitation of chitin-induced plant defenses. In contrast to C. fulvum Ecp6, both Mg1LysM and Mg3LysM also protected fungal hyphae against plant-derived hydrolytic enzymes, and both genes show significantly more nucleotide polymorphism giving rise to nonsynonymous amino acid changes. While Mg1LysM deletion mutant strains of M. graminicola were fully pathogenic toward wheat leaves, Mg3LysM mutant strains were severely impaired in leaf colonization, did not trigger lesion formation, and were unable to undergo asexual sporulation. This virulence defect correlated with more rapid and pronounced expression of wheat defense genes during the symptomless phase of leaf colonization. These data highlight different functions for MgLysM effector homologs during plant infection, including novel activities that distinguish these proteins from C. fulvum Ecp6.

Journal ArticleDOI
TL;DR: Starch is the major storage carbohydrate in higher plants, with many important functions, in photosynthesizing leaves, and is remobilized at night to support continued respiration, Suc export, and growth in the dark.
Abstract: Starch is the major storage carbohydrate in higher plants, with many important functions. In photosynthesizing leaves, starch accumulates during the day and is remobilized at night to support continued respiration, Suc export, and growth in the dark ([Geiger and Servaites, 1994][1]). In this context

Journal ArticleDOI
TL;DR: It is suggested that transgenic approaches to enhance Pi acquisition from paddy soil through the overexpression of Pi transporters may not increase As accumulation in rice grain.
Abstract: Arsenic (As) accumulation in rice (Oryza sativa) may pose a significant health risk to consumers. Plants take up different As species using various pathways. Here, we investigated the contribution of the phosphate (Pi) transport pathway to As accumulation in rice grown hydroponically or under flooded soil conditions. In hydroponic experiments, a rice mutant defective in OsPHF1 (for phosphate transporter traffic facilitator1) lost much of the ability to take up Pi and arsenate and to transport them from roots to shoots, whereas transgenic rice overexpressing either the Pi transporter OsPht1;8 (OsPT8) or the transcription factor OsPHR2 (for phosphate starvation response2) had enhanced abilities of Pi and arsenate uptake and translocation. OsPT8 was found to have a high affinity for both Pi and arsenate, and its overexpression increased the maximum influx by 3- to 5-fold. In arsenate-treated plants, both arsenate and arsenite were detected in the xylem sap, with the proportion of the latter increasing with the exposure time. Under the flooded soil conditions, the phf1 mutant took up less Pi whereas the overexpression lines took up more Pi. But there were no similar effects on As accumulation and distribution. Rice grain contained predominantly dimethylarsinic acid and arsenite, with arsenate being a minor species. These results suggest that the Pi transport pathway contributed little to As uptake and transport to grain in rice plants grown in flooded soil. Transgenic approaches to enhance Pi acquisition from paddy soil through the overexpression of Pi transporters may not increase As accumulation in rice grain.