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The ability of plants to absorb CO2 for photosynthesis and transport water from root to shoot depends on the reversible swelling of guard cells that open stomatal pores in the epidermis. Despite decades of experimental and theoretical work, the biomechanical drivers of stomatal opening and closure are still not clearly defined. We combined mechanical principles with a growing body of knowledge concerning water flux across the plant cell membrane and the biomechanical properties of plant cell walls to quantitatively test the long-standing hypothesis that increasing turgor pressure resulting from water uptake drives guard cell expansion during stomatal opening. To test the alternative hypothesis that water influx is the main motive force underlying guard cell expansion, we developed a system dynamics model accounting for water influx. This approach connects stomatal kinetics to whole plant physiology by including values for water flux arising from water status in the plant .

Pectin is a critical component of the plant cell wall, supporting wall biomechanics and contributing to cell wall signaling in response to stress. The plant cell carefully regulates pectin methylesterification with endogenous pectin methylesterases (PMEs) and their inhibitors (PMEIs) to promote growth and protect against pathogens. We expressed Aspergillus nidulans pectin methylesterase (AnPME) in Arabidopsis thaliana plants to determine the impacts of methylesterification status on pectin function. Plants expressing AnPME had a roughly 50% reduction in methylester content compared with control plants. AnPME plants displayed a severe dwarf phenotype, including small, bushy rosettes and shorter roots. This phenotype was caused by a reduction in cell elongation. Cell wall composition was altered in AnPME plants, with significantly more arabinose and significantly less galacturonic acid, suggesting that plants actively monitor and compensate for altered pectin content. Cell walls of AnPME plants were more readily degraded by polygalacturonase (PG) alone but were less susceptible to treatment with a mixture of PG and PME. AnPME plants were insensitive to osmotic stress, and their susceptibility to Botrytis cinerea was comparable to wild type plants despite their compromised cell walls. This is likely due to upregulated expression of defense response genes observed in AnPME plants. These results demonstrate the importance of pectin in both normal growth and development, and in response to biotic and abiotic stresses.

Guard cells are pairs of epidermal cells that control gas diffusion by regulating the opening and closure of stomatal pores. Guard cells, like other types of plant cells, are surrounded by a three-dimensional, extracellular network of polysaccharide-based wall polymers. In contrast to the walls of diffusely growing cells, guard cell walls have been hypothesized to be uniquely strong and elastic to meet the functional requirements of withstanding high turgor and allowing for reversible stomatal movements. Although the walls of guard cells were long underexplored as compared to extensive studies of stomatal development and guard cell signaling, recent research has provided new genetic, cytological, and physiological data demonstrating that guard cell walls function centrally in stomatal development and dynamics. In this review, we highlight and discuss the latest evidence for how wall polysaccharides are synthesized, deposited, reorganized, modified, and degraded in guard cells, and how these processes influence stomatal form and function. We also raise open questions and provide a perspective on experimental approaches that could be used in the future to shed light on the composition and architecture of guard cell walls.

The ability of plants to absorb CO2 for photosynthesis and transport water from root to shoot depends on the reversible swelling of guard cells that open stomatal pores in the epidermis. Despite decades of experimental and theoretical work, the biomechanical drivers of stomatal opening and closure are still not clearly defined. We combined mechanical principles with a growing body of knowledge concerning water flux across the plant cell membrane and the biomechanical properties of plant cell walls to quantitatively test the long-standing hypothesis that increasing turgor pressure resulting from water uptake drives guard cell expansion during stomatal opening. To test the alternative hypothesis that water influx is the main motive force underlying guard cell expansion, we developed a system dynamics model accounting for water influx. This approach connects stomatal kinetics to whole plant physiology by including values for water flux arising fromwater status in the plant. [ABSTRACT FROM AUTHOR]

Stomatal pores are vital for the diffusion of gasses into and out of land plants and are, therefore, gatekeepers for photosynthesis and transpiration. Although much published literature has described the intercellular signaling and transcriptional regulators involved in early stomatal development, little is known about the cellular details of the local separation between sister guard cells that give rise to the stomatal pore or how formation of this pore is achieved. Using three-dimensional (3D) time-lapse imaging, we found that stomatal pore formation in Arabidopsis (Arabidopsis thaliana) is a highly dynamic process involving pore initiation and enlargement and traverses a set of morphological milestones in 3D. Confocal imaging data revealed an enrichment of exocytic machinery, de-methyl-esterified pectic homogalacturonan (HG), and an HG-degrading enzyme at future pore sites, suggesting that both localized HG deposition and degradation might function in pore formation. By manipulating HG modification via enzymatic, chemical, and genetic perturbations in seedling cotyledons, we found that augmenting HG modification promotes pore formation, whereas preventing HG de-methyl-esterification delays pore initiation and inhibits pore enlargement. Through mechanical modeling and experimentation, we tested whether pore formation is an outcome of sister guard cells being pulled away from each other upon turgor increase. Osmotic treatment to reduce turgor pressure did not prevent pore initiation but did lessen pore enlargement. Together, these data provide evidence that HG delivery and modification, and guard cell pressurization, make functional contributions to stomatal pore initiation and enlargement. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is an essential micronutrient but can be cytotoxic when present in excess. Plants have evolved mechanisms to tolerate Zn toxicity. To identify genetic loci responsible for natural variation of plant tolerance to Zn toxicity, we conduct genome-wide association studies for root growth responses to high Zn and identify 21 significant associated loci. Among these loci, we identify Trichome Birefringence (TBR) allelic variation determining root growth variation in high Zn conditions. Natural alleles of TBR determine TBR transcript and protein levels which affect pectin methylesterification in root cell walls. Together with previously published data showing that pectin methylesterification increase goes along with decreased Zn binding to cell walls in TBR mutants, our findings lead to a model in which TBR allelic variation enables Zn tolerance through modulating root cell wall pectin methylesterification. The role of TBR in Zn tolerance is conserved across dicot and monocot plant species. Zinc is an essential micronutrient for plants, however its excess causes cellular damage. Here, the authors report that natural variation of Trichome Birefringence (TBR) gene confers zinc toxicity tolerance through modulating root cell wall pectin methylesterification in Arabidopsis. [ABSTRACT FROM AUTHOR]

There are more than 100 GDSL lipases in Arabidopsis , but only a few members have been functionally investigated. Moreover, no reports have ever given a comprehensive analysis of GDSLs in stomatal biology. Here, we systematically investigated the expression patterns of 19 putative G uard-cell-enriched G DSL L ipases (GGLs) at various developmental stages and in response to hormone and abiotic stress treatments. Gene expression analyses showed that these GGLs had diverse expression patterns. Fifteen GGLs were highly expressed in guard cells, with seven preferentially in guard cells. Most GGLs were localized in endoplasmic reticulum, and some were also localized in lipid droplets and nucleus. Some closely homologous GGLs exhibited similar expression patterns at various tissues and in response to hormone and abiotic stresses, or similar subcellular localization, suggesting the correlation of expression pattern and biological function, and the functional redundancy of GGLs in plant development and environmental adaptations. Further phenotypic identification of ggl mutants revealed that GGL7 , GGL14 , GGL22 , and GGL26 played unique and redundant roles in stomatal dynamics, stomatal density and morphology, and plant water relation. The present study provides unique resources for functional insights into these GGLs to control stomatal dynamics and development, plant growth, and adaptation to the environment. [ABSTRACT FROM AUTHOR]

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Summary: Herbivore‐induced plant volatiles (HIPVs) are widely recognized as an ecologically important defensive response of plants against herbivory. Although the induction of this 'cry for help' has been well documented, only a few studies have investigated the inhibition of HIPVs by herbivores and little is known about whether herbivores have evolved mechanisms to inhibit the release of HIPVs.To examine the role of herbivore effectors in modulating HIPVs and stomatal dynamics, we conducted series of experiments combining pharmacological, surgical, genetic (CRISPR‐Cas9) and chemical (GC‐MS analysis) approaches.We show that the salivary enzyme, glucose oxidase (GOX), secreted by the caterpillar Helicoverpa zea on leaves, causes stomatal closure in tomato (Solanum lycopersicum) within 5 min, and in both tomato and soybean (Glycine max) for at least 48 h. GOX also inhibits the emission of several HIPVs during feeding by H. zea, including (Z)‐3‐hexenol, (Z)‐jasmone and (Z)‐3‐hexenyl acetate, which are important airborne signals in plant defenses.Our findings highlight a potential adaptive strategy where an insect herbivore inhibits plant airborne defenses during feeding by exploiting the association between stomatal dynamics and HIPV emission. [ABSTRACT FROM AUTHOR]

In plants, stomatal guard cells are one of the most dynamic cell types, rapidly changing their shape and size in response to environmental and intrinsic signals to control gas exchange at the plant surface. Quantitative and systematic knowledge of the biomechanical underpinnings of stomatal dynamics will enable strategies to optimize stomatal responsiveness and improve plant productivity by enhancing the efficiency of photosynthesis and water use. Recent developments in microscopy, mechanical measurements, and computational modeling have revealed new insights into the biomechanics of stomatal regulation and the genetic, biochemical, and structural origins of how plants achieve rapid and reliable stomatal function by tuning the mechanical properties of their guard cell walls. This review compares historical and recent experimental and modeling studies of the biomechanics of stomatal complexes, highlighting commonalities and contrasts between older and newer studies. Key gaps in our understanding of stomatal functionality are also presented, along with assessments of potential methods that could bridge those gaps. [ABSTRACT FROM AUTHOR]

Guard cells are pairs of epidermal cells that control gas diffusion by regulating the opening and closure of stomatal pores. Guard cells, like other types of plant cells, are surrounded by a three-dimensional, extracellular network of polysaccharide-based wall polymers. In contrast to the walls of diffusely growing cells, guard cell walls have been hypothesized to be uniquely strong and elastic to meet the functional requirements of withstanding high turgor and allowing for reversible stomatal movements. Although the walls of guard cells were long underexplored as compared to extensive studies of stomatal development and guard cell signaling, recent research has provided new genetic, cytological, and physiological data demonstrating that guard cell walls function centrally in stomatal development and dynamics. In this review, we highlight and discuss the latest evidence for how wall polysaccharides are synthesized, deposited, reorganized, modified, and degraded in guard cells, and how these processes influence stomatal form and function. We also raise open questions and provide a perspective on experimental approaches that could be used in the future to shed light on the composition and architecture of guard cell walls. [ABSTRACT FROM AUTHOR]

γ-Secretase has been a therapeutical target for its key role in cleaving APP to generate β-amyloid (Aβ), the primary constituents of senile plaques and a hallmark of Alzheimer’s disease (AD) pathology. Recently, γ-secretase-associating proteins showed promising role in specifically modulating APP processing while sparing Notch signaling; however, the underlying mechanism is still unclear. A co-immunoprecipitation (Co-IP) coupled with mass spectrometry proteomic assay for Presenilin1 (PS1, the catalytic subunit of γ-secretase) was firstly conducted to find more γ-secretase-associating proteins. Gene ontology analysis of these results identified Rab21 as a potential PS1 interacting protein, and the interaction between them was validated by reciprocal Co-IP and immunofluorescence assay. Then, molecular and biochemical methods were used to investigate the effect of Rab21 on APP processing. Results showed that overexpression of Rab21 enhanced Aβ generation, while silencing of Rab21 reduced the accumulation of Aβ, which resulted due to change in γ-secretase activity rather than α- or β-secretase. Finally, we demonstrated that Rab21 had no effect on γ-secretase complex synthesis or metabolism but enhanced PS1 endocytosis and translocation to late endosome/lysosome. In conclusion, we identified a novel γ-secretase-associating protein Rab21 and illustrate that Rab21 promotes γ-secretase internalization and translocation to late endosome/lysosome. Moreover, silencing of Rab21 decreases the γ-secretase activity in APP processing thus production of Aβ. All these results open new gateways towards the understanding of γ-secretase-associating proteins in APP processing and make inhibition of Rab21 a promising strategy for AD therapy. [ABSTRACT FROM AUTHOR]

Pectin is a critical component of the plant cell wall, supporting wall biomechanics and contributing to cell wall signaling in response to stress. The plant cell carefully regulates pectin methylesterification with endogenous pectin methylesterases (PMEs) and their inhibitors (PMEIs) to promote growth and protect against pathogens. We expressed Aspergillus nidulans pectin methylesterase (AnPME) in Arabidopsis thaliana plants to determine the impacts of methylesterification status on pectin function. Plants expressing AnPME had a roughly 50% reduction in methylester content compared with control plants. AnPME plants displayed a severe dwarf phenotype, including small, bushy rosettes and shorter roots. This phenotype was caused by a reduction in cell elongation. Cell wall composition was altered in AnPME plants, with significantly more arabinose and significantly less galacturonic acid, suggesting that plants actively monitor and compensate for altered pectin content. Cell walls of AnPME plants were more readily degraded by polygalacturonase (PG) alone but were less susceptible to treatment with a mixture of PG and PME. AnPME plants were insensitive to osmotic stress, and their susceptibility to Botrytis cinerea was comparable to wild type plants despite their compromised cell walls. This is likely due to upregulated expression of defense response genes observed in AnPME plants. These results demonstrate the importance of pectin in both normal growth and development, and in response to biotic and abiotic stresses. [ABSTRACT FROM AUTHOR]