Cell Wall In Response Research Articles

The effect of biochar amendment on Cd accumulation in Bidens pilosa L: Changing Cd subcellular distribution, cell wall polysaccharide Cd-binding capacity and composition

Biochar can reduce Cd uptake by plants, thereby reducing its biotoxicity, but the mechanisms involved at the subcellular level have not been thoroughly elucidated. In this work, we explored the effect of maize straw biochar on Cd accumulation by Bidens pilosa L. and its mechanism at subcellular levels. After 90 days of potting experiment, the subcellular fractions were extracted by differential centrifugation, and the polysaccharide fractions of root cell walls were extracted by leaching centrifugation, and then the Cd content of each fraction was determined. Results showed that Cd was preferentially distributed in cell walls of three organs. Additionally, biochar addition resulted in a greater distribution of Cd from cell wall to soluble fractions and organelles in stems. These results suggested that cell wall immobilization and intracellular compartmentalization were critical detoxification mechanisms tackling Cd stress with biochar addition of Bidens pilosa L. Pectin was the main sink where Cd was stored. And galacturonic acid content in pectin occupied the highest ratio among the three polysaccharide fractions. After biochar addition, in hemicellulose the change of Cd content was consistent with the change of galacturonic acid content. These results suggested that the galacturonic acid in hemicellulose played an important role in Cd binding. Biochar addition reduced the bioavailability of soil Cd and improved the growth environment, thus inducing Bidens pilosa L. to change the composition of root cell wall in response to Cd stress.

Structural diversification of fungal cell wall in response to the stress signaling and remodeling during fungal pathogenesis

Structural diversification of fungal cell wall in response to the stress signaling and remodeling during fungal pathogenesis

Vibrational spectroscopic profiling of biomolecular interactions between oak powdery mildew and oak leaves.

Oak powdery mildew, caused by the biotrophic fungus Erysiphe alphitoides, is a prevalent disease affecting oak trees, such as English oak (Quercus robur). While mature oak populations are generally less susceptible to this disease, it can endanger young oak seedlings and new leaves on mature trees. Although disruptions of photosynthate and carbohydrate translocation have been observed, accurately detecting and understanding the specific biomolecular interactions between the fungus and the leaves of oak trees is currently lacking. Herein, via hybrid Raman spectroscopy combined with an advanced artificial neural network algorithm, the underpinning biomolecular interactions between biological soft matter, i.e., Quercus robur leaves and Erysiphe alphitoides, are investigated and profiled, generating a spectral library and shedding light on the changes induced by fungal infection and the tree's defence response. The adaxial surfaces of oak leaves are categorised based on either the presence or absence of Erysiphe alphitoides mildew and further distinguishing between covered or not covered infected leaf tissues, yielding three disease classes including healthy controls, non-mildew covered and mildew-covered. By analysing spectral changes between each disease category per tissue type, we identified important biomolecular interactions including disruption of chlorophyll in the non-vein and venule tissues, pathogen-induced degradation of cellulose and pectin and tree-initiated lignification of cell walls in response, amongst others, in lateral vein and mid-vein tissues. Via our developed computational algorithm, the underlying biomolecular differences between classes were identified and allowed accurate and rapid classification of disease with high accuracy of 69.6% for non-vein, 73.5% for venule, 82.1% for lateral vein and 85.6% for mid-vein tissues. Interfacial wetting differences between non-mildew covered and mildew-covered tissue were further analysed on the surfaces of non-vein and venule tissue. The overall results demonstrated the ability of Raman spectroscopy, combined with advanced AI, to act as a powerful and specific tool to probe foliar interactions between forest pathogens and host trees with the simultaneous potential to probe and catalogue molecular interactions between biological soft matter, paving the way for exploring similar relations in broader forest tree-pathogen systems.

The Role of Dietary Supplementation of Yeast Cell Walls in Response to a Campylobacter jejuni Inoculation in Broiler Chickens.

Controlling Campylobacter jejuni during broiler production is a topic of interest from a public health standpoint, as colonized birds can contaminate poultry products during processing and sicken humans if not properly cooked or handled before consumption. The aim of this study was to evaluate dietary yeast cell wall (YCW) as a potential alternative to antibiotic growth promoters with or without a C. jejuni challenge. A total of 2240 day-old Ross 708 males were randomly assigned within 8 experimental groups with a 4 × 2 factorial design, with 4 diets (negative control [CTL-], positive control [CTL+, bacitracin, 50 g/ ton], YCW constant dose [400 g/ton], and YCW step-down dose [SD, 800, 400, and 200 g/ton in the starter, grower, and finisher periods, respectively]) and with or without a Day-16 C. jejuni oral gavage challenge at a 103-colony-forming-units (CFU)/ml dose. Body weights and feed consumption were measured on Days 0, 14, 28, and 41 to determine broiler performance. Ileum tissue samples were collected from 24 birds per treatment on Days 17 and 24 (1 and 8 days postinoculation [PI]) for relative gene expression (RGE) analysis. Cecal content samples were collected from 24 birds per treatment on Days 24, 34, and 42 for C. jejuni enumeration and prevalence calculation. A total of 80 birds per treatment were processed to determine carcass yield on Day 44, and on Day 45, 16 carcass rinsates per treatment were collected for C. jejuni enumeration and prevalence calculation. The interaction between diet and inoculation did not influence growth performance (P > 0.05). However, a diet effect was observed in the starter period where birds fed SD diet had a lower feed conversion ratio than birds fed CTL- diet (P = 0.0165). Additionally, the treatment of birds inoculated with C. jejuni fed with SD had a trend to a lower feed conversion ratio during the grower period (P = 0.0550). The RGE of interleukin 1β and interleukin 10 was similar in all treatments 1 and 8 days PI. The RGE of avian beta defensin 10 was similar in all treatments on Day 1 PI, but different on Day 8 PI (P = 0.0476). All birds inoculated with C. jejuni had similar CFU per milliliter counts in the cecal contents at Days 24, 34, and 42 (P > 0.05), and all birds inoculated with phosphate-buffered saline were negative for C. jejuni after prevalence testing. After processing 1) carcass yield was similar in all treatments (P > 0.05); 2) C. jejuni-inoculated birds fed CTL- had lower CFU per milliliter counts than birds provided CTL+ and constant-dose diets (P = 0.0383); and 3) all birds inoculated with PBS were negative for Campylobacter. Overall, under the conditions of this study, the addition of YCW during a C. jejuni challenge did not have an impact on growth performance, innate immune response, cecal colonization, carcass yield, or carcass colonization after processing.

Caspofungin-induced β(1,3)-glucan exposure in Candida albicans is driven by increased chitin levels.

To successfully induce disease, Candida albicans must effectively evade the host immune system. One mechanism used by C. albicans to achieve this is to mask immunogenic β(1,3)-glucan epitopes within its cell wall under an outer layer of mannosylated glycoproteins. Consequently, induction of β(1,3)-glucan exposure (unmasking) via genetic or chemical manipulation increases fungal recognition by host immune cells in vitro and attenuates disease during systemic infection in mice. Treatment with the echinocandin caspofungin is one of the most potent drivers of β(1,3)-glucan exposure. Several reports using murine infection models suggest a role for the immune system, and specifically host β(1,3)-glucan receptors, in mediating the efficacy of echinocandin treatment in vivo. However, the mechanism by which caspofungin-induced unmasking occurs is not well understood. In this report, we show that foci of unmasking co-localize with areas of increased chitin within the yeast cell wall in response to caspofungin, and that inhibition of chitin synthesis via nikkomycin Z attenuates caspofungin-induced β(1,3)-glucan exposure. Furthermore, we find that both the calcineurin and Mkc1 mitogen-activated protein kinase pathways work synergistically to regulate β(1,3)-glucan exposure and chitin synthesis in response to drug treatment. When either of these pathways are interrupted, it results in a bimodal population of cells containing either high or low chitin content. Importantly, increased unmasking correlates with increased chitin content within these cells. Microscopy further indicates that caspofungin-induced unmasking correlates with actively growing cells. Collectively, our work presents a model in which chitin synthesis induces unmasking within the cell wall in response to caspofungin in growing cells. IMPORTANCE Systemic candidiasis has reported mortality rates ranging from 20% to 40%. The echinocandins, including caspofungin, are first-line antifungals used to treat systemic candidiasis. However, studies in mice have shown that echinocandin efficacy relies on both its cidal impacts on Candida albicans, as well as a functional immune system to successfully clear invading fungi. In addition to direct C. albicans killing, caspofungin increases exposure (unmasking) of immunogenic β(1,3)-glucan moieties. To evade immune detection, β(1,3)-glucan is normally masked within the C. albicans cell wall. Consequently, unmasked β(1,3)-glucan renders these cells more visible to the host immune system and attenuates disease progression. Therefore, discovery of how caspofungin-induced unmasking occurs is needed to elucidate how the drug facilitates host immune system-mediated clearance in vivo. We report a strong and consistent correlation between chitin deposition and unmasking in response to caspofungin and propose a model in which altered chitin synthesis drives increased unmasking during drug exposure.

Sub-cell scale features govern the placement of new cells by honeybees during comb construction

Honeybee comb architecture and the manner of its construction have long been the subject of scientific curiosity. Comb is characterised by an even hexagonal layout and the sharing of cell bases and side walls, which provides maximised storage volume while requiring minimal wax. The efficiency of this structure relies on a regular layout and the correct positioning of cells relative to each other, with each new cell placed at the junction of two previously constructed cells. This task is complicated by the incomplete nature of cells at the edge of comb, where new cells are to be built. We presented bees with wax stimuli comprising shallow depressions and protuberances in simulation of features found within partially formed comb, and demonstrated that construction work by honeybee builders was influenced by these stimuli. The building of new cells was aligned to concave stimuli that simulated the clefts that naturally appear between two partially formed cells, revealing how new cells may be aligned to ensure proper tessellation within comb. We also found that bees built cell walls in response to edges formed by our stimuli, suggesting that cell and wall construction was specifically directed towards the locations necessary for continuation of hexagonal comb.

Characterization of MdMYB68, a suberin master regulator in russeted apples.

Apple russeting is mainly due to the accumulation of suberin in the cell wall in response to defects and damages in the cuticle layer. Over the last decades, massive efforts have been done to better understand the complex interplay between pathways involved in the suberization process in model plants. However, the regulation mechanisms which orchestrate this complex process are still under investigation. Our previous studies highlighted a number of transcription factor candidates from the Myeloblastosis (MYB) transcription factor family which might regulate suberization in russeted or suberized apple fruit skin. Among these, we identified MdMYB68, which was co-expressed with number of well-known key suberin biosynthesis genes. To validate the MdMYB68 function, we conducted an heterologous transient expression in Nicotiana benthamiana combined with whole gene expression profiling analysis (RNA-Seq), quantification of lipids and cell wall monosaccharides, and microscopy. MdMYB68 overexpression is able to trigger the expression of the whole suberin biosynthesis pathway. The lipid content analysis confirmed that MdMYB68 regulates the deposition of suberin in cell walls. Furthermore, we also investigated the alteration of the non-lipid cell wall components and showed that MdMYB68 triggers a massive modification of hemicelluloses and pectins. These results were finally supported by the microscopy. Once again, we demonstrated that the heterologous transient expression in N. benthamiana coupled with RNA-seq is a powerful and efficient tool to investigate the function of suberin related transcription factors. Here, we suggest MdMYB68 as a new regulator of the aliphatic and aromatic suberin deposition in apple fruit, and further describe, for the first time, rearrangements occurring in the carbohydrate cell wall matrix, preparing this suberin deposition.

Cryptococcus neoformans Mar1 function links mitochondrial metabolism, oxidative stress, and antifungal tolerance.

Introduction: Microbial pathogens undergo significant physiological changes during interactions with the infected host, including alterations in metabolism and cell architecture. The Cryptococcus neoformans Mar1 protein is required for the proper ordering of the fungal cell wall in response to host-relevant stresses. However, the precise mechanism by which this Cryptococcus-specific protein regulates cell wall homeostasis was not defined. Methods: Here, we use comparative transcriptomics, protein localization, and phenotypic analysis of a mar1D loss-of-function mutant strain to further define the role of C. neoformans Mar1 in stress response and antifungal resistance. Results: We demonstrate that C. neoformans Mar1 is highly enriched in mitochondria. Furthermore, a mar1Δ mutant strain is impaired in growth in the presence of select electron transport chain inhibitors, has altered ATP homeostasis, and promotes proper mitochondrial morphogenesis. Pharmacological inhibition of complex IV of the electron transport chain in wild-type cells promotes similar cell wall changes as the mar1Δ mutant strain, supporting prior associations between mitochondrial function and cell wall homeostasis. Although Mar1 is not required for general susceptibility to the azole antifungals, the mar1Δ mutant strain displays increased tolerance to fluconazole that correlates with repressed mitochondrial metabolic activity. Discussion: Together, these studies support an emerging model in which the metabolic activity of microbial cells directs cell physiological changes to allow persistence in the face of antimicrobial and host stress.

The Pga59 cell wall protein is an amyloid forming protein involved in adhesion and biofilm establishment in the pathogenic yeast Candida albicans

The human commensal fungus Candida albicans can attach to epithelia or indwelling medical devices and form biofilms, that are highly tolerant to antifungal drugs and can evade the immune response. The cell surface protein Pga59 has been shown to influence adhesion and biofilm formation. Here, we present evidence that Pga59 displays amyloid properties. Using electron microscopy, staining with an amyloid fibre-specific dye and X-ray diffraction experiments, we showed that the predicted amyloid-forming region of Pga59 is sufficient to build up an amyloid fibre in vitro and that recombinant Pga59 can also adopt a cross-β amyloid fibre architecture. Further, mutations impairing Pga59 amyloid assembly led to diminished adhesion to substrates and reduced biofilm production. Immunogold labelling on amyloid structures extracted from C. albicans revealed that Pga59 is used by the fungal cell to assemble amyloids within the cell wall in response to adhesion. Altogether, our results suggest that Pga59 amyloid properties are used by the fungal cell to mediate cell-substrate interactions and biofilm formation.

Activity of Cytosolic Ascorbate Peroxidase (APX) from Panicum virgatum against Ascorbate and Phenylpropanoids.

APX is a key antioxidant enzyme in higher plants, scavenging H2O2 with ascorbate in several cellular compartments. Here, we report the crystal structures of cytosolic ascorbate peroxidase from switchgrass (Panicum virgatum L., Pvi), a strategic feedstock plant with several end uses. The overall structure of PviAPX was similar to the structures of other APX family members, with a bound ascorbate molecule at the ɣ-heme edge pocket as in other APXs. Our results indicated that the H2O2-dependent oxidation of ascorbate displayed positive cooperativity. Significantly, our study suggested that PviAPX can oxidize a broad range of phenylpropanoids with δ-meso site in a rather similar efficiency, which reflects its role in the fortification of cell walls in response to insect feeding. Based on detailed structural and kinetic analyses and molecular docking, as well as that of closely related APX enzymes, the critical residues in each substrate-binding site of PviAPX are proposed. Taken together, these observations shed new light on the function and catalysis of PviAPX, and potentially benefit efforts improve plant health and biomass quality in bioenergy and forage crops.

Effects of hot water, calcium chloride and 1-MCP on the activity of cell wall degrading enzymes in sweet cherry (Prunus avium)

The objective of the study was to determine the changes in the activities of the enzymes degrading the cell wall in response to hot water, calcium chloride (CaCl2) and 1-methlylcyclopropene (1-MCP) treatments during post-harvest storage in the sweet cherries. For this purpose, 0.5, 1, and 5 μl L-1 1-MCP, 1% and 2% CaCl2 and 45, 50, and 55 oC hot waters were applied to the sweet cherries. As a result of the study conducted with the enzymes degrading the cell wall, it was observed that very significant increases occured during the storage in the activities of polygalacturonase, pectin methyl esterase, xyloglucanase, beta 1-4 endoglucanase and alpha and beta galactosidases. Therefore, it seems that these enzymes make a significant contribution to the softening observed during the storage after harvesting in sweet cherries. The changes observed in the activities of the enzymes degrading the cell wall have been significantly reduced by the treatments. As a result, 1-MCP, CaCl2 and hot water treatmens can be used to prolong the postharvest life in sweet cherries by delaying the softening and preventing the quality losses observed after harvesting in the cherries.

How Cell Geometry and Cellular Patterning Influence Tissue Stiffness.

Cell growth in plants occurs due to relaxation of the cell wall in response to mechanical forces generated by turgor pressure. Growth can be anisotropic, with the principal direction of growth often correlating with the direction of lower stiffness of the cell wall. However, extensometer experiments on onion epidermal peels have shown that the tissue is stiffer in the principal direction of growth. Here, we used a combination of microextensometer experiments on epidermal onion peels and finite element method (FEM) modeling to investigate how cell geometry and cellular patterning affects mechanical measurements made at the tissue level. Simulations with isotropic cell-wall material parameters showed that the orientation of elongated cells influences tissue apparent stiffness, with the tissue appearing much softer in the transverse versus the longitudinal directions. Our simulations suggest that although extensometer experiments show that the onion tissue is stiffer when stretched in the longitudinal direction, the effect of cellular geometry means that the wall is in fact softer in this direction, matching the primary growth direction of the cells.

Differential Requirement for the Cell Wall Integrity Sensor Wsc1p in Diploids Versus Haploids.

The primary role of the Cell Wall Integrity Pathway (CWI) in Saccharomyces cerevisiae is monitoring the state of the cell wall in response to general life cycle stresses (growth and mating) and imposed stresses (temperature changes and chemicals). Of the five mechanosensor proteins monitoring cell wall stress, Wsc1p and Mid2p are the most important. We find that WSC1 has a stringent requirement in zygotes and diploids, unlike haploids, and differing from MID2’s role in shmoos. Diploids lacking WSC1 die frequently, independent of mating type. Death is due to loss of cell wall and plasma membrane integrity, which is suppressed by osmotic support. Overexpression of several CWI pathway components suppress wsc1∆ zygotic death, including WSC2, WSC3, and BEM2, as well as the Rho-GAPS, BEM3 and RGD2. Microscopic observations and suppression by BEM2 and BEM3 suggest that wsc1∆ zygotes die during bud emergence. Downstream in the CWI pathway, overexpression of a hyperactive protein kinase C (Pkc1p-R398P) causes growth arrest, and blocks the pheromone response. With moderate levels of Pkc1p-R398P, cells form zygotes and the wsc1∆ defect is suppressed. This work highlights functional differences in the requirement for Wsc1p in diploids Versus haploids and between Mid2p and Wsc1p during mating.

Appressorium-mediated plant infection by Magnaporthe oryzae is regulated by a Pmk1-dependent hierarchical transcriptional network.

Rice blast is a devastating disease caused by the fungal pathogen Magnaporthe oryzae that threatens rice production around the world. The fungus produces a specialized infection cell, called the appressorium, that enables penetration through the plant cell wall in response to surface signals from the rice leaf. The underlying biology of plant infection, including the regulation of appressorium formation, is not completely understood. Here we report the identification of a network of temporally coregulated transcription factors that act downstream of the Pmk1 mitogen-activated protein kinase pathway to regulate gene expression during appressorium-mediated plant infection. We show that this tiered regulatory mechanism involves Pmk1-dependent phosphorylation of the Hox7 homeobox transcription factor, which regulates genes associated with induction of major physiological changes required for appressorium development-including cell-cycle control, autophagic cell death, turgor generation and melanin biosynthesis-as well as controlling a additional set of virulence-associated transcription factor-encoding genes. Pmk1-dependent phosphorylation of Mst12 then regulates gene functions involved in septin-dependent cytoskeletal re-organization, polarized exocytosis and effector gene expression, which are necessary for plant tissue invasion. Identification of this regulatory cascade provides new potential targets for disease intervention.

Cell wall deficiency as an escape mechanism from phage infection.

The cell wall plays a central role in protecting bacteria from some environmental stresses, but not against all. In fact, in some cases, an elaborate cell envelope may even render the cell more vulnerable. For example, it contains molecules or complexes that bacteriophages recognize as the first step of host invasion, such as proteins and sugars, or cell appendages such as pili or flagella. In order to counteract phages, bacteria have evolved multiple escape mechanisms, such as restriction-modification, abortive infection, CRISPR/Cas systems or phage inhibitors. In this perspective review, we present the hypothesis that bacteria may have additional means to escape phage attack. Some bacteria are known to be able to shed their cell wall in response to environmental stresses, yielding cells that transiently lack a cell wall. In this wall-less state, the bacteria may be temporarily protected against phages, since they lack the essential entities that are necessary for phage binding and infection. Given that cell wall deficiency can be triggered by clinically administered antibiotics, phage escape could be an unwanted consequence that limits the use of phage therapy for treating stubborn infections.

Change in Micromechanical Behavior of Surface Densified Wood Cell Walls in Response to Superheated Steam Treatment

The combination of surface densification and superheated steam treatment is an effective method to improve the mechanical properties and dimensional stability of low-density wood. The objective of the current work is to evaluate the effects of superheated steam treatment on the micromechanical behavior of surface densified wood. The microstructure, chemical composition, cellulose crystalline structure, and micromechanical behavior of surface densified wood under different superheated steam pressures were investigated. Results indicated that both 0.1 MPa and 0.3 MPa superheated steam treatments increased the elastic modulus and hardness of fiber cell walls in surface densified wood. However, the average creep ratio and maximum creep compliance J(50) of surface densified wood under 0.3 MPa decreased by 41.59% and 6.76%, respectively, compared with untreated wood. The improvement of elastic modulus, hardness and creep resistance of surface densified wood treated with superheated steam was associated with the increase of relative crystallinity (CrI) and crystalline size. In addition, 0.3 MPa superheated steam treatment displayed a better effect on the enhancement of the elastic modulus, hardness, and creep resistance of the fiber cell wall than 0.1 MPa superheated steam treatment.

Plant Cell Wall as a Key Player During Resistant and Susceptible Plant-Virus Interactions.

The cell wall is a complex and integral part of the plant cell. As a structural element it sustains the shape of the cell and mediates contact among internal and external factors. We have been aware of its involvement in both abiotic (like drought or frost) and biotic stresses (like bacteria or fungi) for some time. In contrast to bacterial and fungal pathogens, viruses are not mechanical destructors of host cell walls, but relatively little is known about remodeling of the plant cell wall in response to viral biotic stress. New research results indicate that the cell wall represents a crucial active component during the plant’s response to different viral infections. Apparently, cell wall genes and proteins play key roles during interaction, having a direct influence on the rebuilding of the cell wall architecture. The plant cell wall is involved in both susceptibility as well as resistance reactions. In this review we summarize important progress made in research on plant virus impact on cell wall remodeling. Analyses of essential defensive wall associated proteins in susceptible and resistant responses demonstrate that the components of cell wall metabolism can affect the spread of the virus as well as activate the apoplast- and symplast-based defense mechanisms, thus contributing to the complex network of the plant immune system. Although the cell wall reorganization during the plant-virus interaction remains a challenging task, the use of novel tools and methods to investigate its composition and structure will greatly contribute to our knowledge in the field.

Immune Sensing of Candida albicans.

Candida albicans infections range from superficial to systemic and are one of the leading causes of fungus-associated nosocomial infections. The innate immune responses during these various infection types differ, suggesting that the host environment plays a key role in modulating the host–pathogen interaction. In addition, C. albicans is able to remodel its cell wall in response to environmental conditions to evade host clearance mechanisms and establish infection in niches, such as the oral and vaginal mucosa. Phagocytes play a key role in clearing C. albicans, which is primarily mediated by Pathogen Associated Molecular Pattern (PAMP)–Pattern Recognition Receptor (PRR) interactions. PRRs such as Dectin-1, DC-SIGN, and TLR2 and TLR4 interact with PAMPs such as β-glucans, N-mannan and O-mannan, respectively, to trigger the activation of innate immune cells. Innate immune cells exhibit distinct yet overlapping repertoires of PAMPs, resulting in the preferential recognition of particular Candida morphotypes by them. The role of phagocytes in the context of individual infection types also differs, with neutrophils playing a prominent role in kidney infections, and dendritic cells playing a prominent role in skin infections. In this review, we provide an overview of the key receptors involved in the detection of C. albicans and discuss the differential innate immune responses to C. albicans seen in different infection types such as vulvovaginal candidiasis (VVC) and oral candidiasis.

Staining and automated image quantification of callose in Arabidopsis cotyledons and leaves.

Callose is a β-1,3-glucan polysaccharide that is deposited at discrete sites in the plant cell wall in response to microbial pathogens, likely contributing to protection against pathogen infection. Increased callose deposition also occurs in response to the 22-amino acid peptide flg22, a pathogen-associated molecular pattern (PAMP) derived from bacterial flagellin protein. Here, we provide protocols for callose staining using aniline blue in cotyledon and leaf tissue of the model plant Arabidopsis thaliana. Aniline blue stain utilizes a fluorochrome that complexes with callose for its visualization by microscopy using an ultraviolet (UV) filter. For robust quantification of callose deposits, we outline an automated image analysis workflow utilizing the freely available Fiji (Fiji Is Just ImageJ; NIH) software and a Trainable Weka Segmentation (TWS) plugin. Our methodology for automated analysis of large batches of images can be easily adapted to quantify callose in other tissues and plant species, as well as to quantify fluorescent structures other than callose.

Feedback from Tissue Mechanics Self-Organizes Efficient Outgrowth of Plant Organ

Plant organ outgrowth superficially appears like the continuous mechanical deformation of a sheet of cells. Yet, how precisely cells as individual mechanical entities can act to morph a tissue reliably and efficiently into three dimensions during outgrowth is still puzzling, especially when cells are tightly connected as in plant tissue. In plants, the mechanics of cells within a tissue is particularly well-defined because individual cell growth is essentially the mechanical yielding of the cell wall in response to internal turgor pressure. Cell-wall stiffness is controlled by biological signaling, which is impacted by stresses, and hence, cell growth is observed to respond to mechanical stresses building up within a tissue. What is the role of the mechanical feedback during morphing of tissue in three dimensions? Here, we develop a three-dimensional vertex model to investigate tissue mechanics at the onset of organ outgrowth at the tip of a plant shoot. We find that organ height is primarily governed by the ratio of growth rates of faster-growing cells initiating the organ versus slower-growing cells surrounding them. Remarkably, the outgrowth rate is higher when cell growth responds to the tissue-wide mechanical stresses. Our quantitative analysis of simulation data shows that tissue mechanical feedback on cell growth can act via a twofold mechanism. First, the feedback guides patterns of cellular growth. Second, the feedback modifies the stress patterns on the cells, consequently amplifying and propagating growth anisotropies. This mechanism may allow plants to grow organs efficiently out of the meristem by reorganizing the cellular growth rather than inflating growth rates.