Search

Introduction: Leptoids, the food-conducting cells of polytrichaceous mosses, share key structural features with sieve elements in tracheophytes, including an elongated shape with oblique end walls containing modified plasmodesmata or pores. In tracheophytes, callose is instrumental in developing the pores in sieve elements that enable efficient photoassimilate transport. Aside from a few studies using aniline blue fluorescence that yielded confusing results, little is known about callose in moss leptoids. Methods: Callose location and abundance during the development of leptoid cell walls was investigated in the moss Polytrichum commune using aniline blue fluorescence and quantitative immunogold labeling (label density) in the transmission electron microscope. To evaluate changes during abiotic stress, callose abundance in leptoids of hydrated plants was compared to plants dried for 14 days under field conditions. A bioinformatic study to assess the evolution of callose within and across bryophytes was conducted using callose synthase (CalS) genes from 46 bryophytes (24 mosses, 15 liverworts, and 7 hornworts) and one representative each of five tracheophyte groups. Results: Callose abundance increases around plasmodesmata from meristematic cells to end walls in mature leptoids. Controlled drying resulted in a significant increase in label density around plasmodesmata and pores over counts in hydrated plants. Phylogenetic analysis of the CalS protein family recovered main clades (A, B, and C). Different from tracheophytes, where the greatest diversity of homologs is found in clade A, the majority of gene duplication in bryophytes is in clade B. Discussion: This work identifies callose as a crucial cell wall polymer around plasmodesmata from their inception to functioning in leptoids, and during water stress similar to sieve elements of tracheophytes. Among bryophytes, mosses exhibit the greatest number of multiple duplication events, while only two duplications are revealed in hornwort and none in liverworts. The absence in bryophytes of the CalS 7 gene that is essential for sieve pore development in angiosperms, reveals that a different gene is responsible for synthesizing the callose associated with leptoids in mosses. [ABSTRACT FROM AUTHOR]

Callose is an important polysaccharide composed of beta-1,3-glucans and is widely implicated in plant development and defense responses. Callose synthesis is mainly catalyzed by a family of callose synthases, also known as glucan synthase-like (GSL) enzymes. Despite the fact that GSL family genes were studied in a few plant species, their functional roles have not been fully understood in woody perennials. In this study, we identified total of 84 GSL genes in seven plant species and classified them into six phylogenetic clades. An evolutionary analysis revealed different modes of duplication driving the expansion of GSL family genes in monocot and dicot species, with strong purifying selection constraining the protein evolution. We further examined the gene structure, protein sequences, and physiochemical properties of 11 GSL enzymes in Prunus mume and observed strong sequence conservation within the functional domain of PmGSL proteins. However, the exon–intron distribution and protein motif composition are less conservative among PmGSL genes. With a promoter analysis, we detected abundant hormonal responsive cis-acting elements and we inferred the putative transcription factors regulating PmGSLs. To further understand the function of GSL family genes, we analyzed their expression patterns across different tissues, and during the process of floral bud development, pathogen infection, and hormonal responses in Prunus species and identified multiple GSL gene members possibly implicated in the callose deposition associated with bud dormancy cycling, pathogen infection, and hormone signaling. In summary, our study provides a comprehensive understanding of GSL family genes in Prunus species and has laid the foundation for future functional research of callose synthase genes in perennial trees. [ABSTRACT FROM AUTHOR]

IntroductionLeptoids, the food-conducting cells of polytrichaceous mosses, share key structural features with sieve elements in tracheophytes, including an elongated shape with oblique end walls containing modified plasmodesmata or pores. In tracheophytes, callose is instrumental in developing the pores in sieve elements that enable efficient photoassimilate transport. Aside from a few studies using aniline blue fluorescence that yielded confusing results, little is known about callose in moss leptoids.MethodsCallose location and abundance during the development of leptoid cell walls was investigated in the moss Polytrichum commune using aniline blue fluorescence and quantitative immunogold labeling (label density) in the transmission electron microscope. To evaluate changes during abiotic stress, callose abundance in leptoids of hydrated plants was compared to plants dried for 14 days under field conditions. A bioinformatic study to assess the evolution of callose within and across bryophytes was conducted using callose synthase (CalS) genes from 46 bryophytes (24 mosses, 15 liverworts, and 7 hornworts) and one representative each of five tracheophyte groups.ResultsCallose abundance increases around plasmodesmata from meristematic cells to end walls in mature leptoids. Controlled drying resulted in a significant increase in label density around plasmodesmata and pores over counts in hydrated plants. Phylogenetic analysis of the CalS protein family recovered main clades (A, B, and C). Different from tracheophytes, where the greatest diversity of homologs is found in clade A, the majority of gene duplication in bryophytes is in clade B. DiscussionThis work identifies callose as a crucial cell wall polymer around plasmodesmata from their inception to functioning in leptoids, and during water stress similar to sieve elements of tracheophytes. Among bryophytes, mosses exhibit the greatest number of multiple duplication events, while only two duplications are revealed in hornwort and none in liverworts. The absence in bryophytes of the CalS 7 gene that is essential for sieve pore development in angiosperms, reveals that a different gene is responsible for synthesizing the callose associated with leptoids in mosses.

Abiotic stress affects plants' growth and development. Soybean is an important crop of the world, however, its production is affected by abiotic stresses. Callose Synthase is the most crucial enzyme response to environmental and developmental signals. However, in soybean, information on the callose synthase genes is limited. In this study, we analyzed the callose synthase gene family of soybean at the genome-wide scale. We also studied the genes positions, gene structure, evolutionary relations, miRNAs target sites, and expression of CalS genes. Resultantly 24 CalS genes were found in soybean, with diverse chromosomal locations, cis-acting elements, conserved motifs, and gene structures. Further, GmCalS genes were divided into four phylogenetic classes. The evolutionary classification of CalSs was supported by the motif and gene structure analyses. Phytohormones, abiotic stresses, and growth-responsive elements were identified in the promoter of GmCalSs. In addition, the GmCalS genes higher expression in roots, leaves, flowers, and nodules tissues provided their significance in development. Furthermore, the higher expression of GmCalS17 and GmCalS19 genes in response to salt stress indicated their importance against salt stress. These findings will be helpful for further investigation of the CalS genes in other crops.

SUMMARY: Ovules are female reproductive organs of angiosperms, consisting of sporophytic integuments surrounding female gametophytes, that is, embryo sacs. Synchronization between integument growth and embryo sac development requires intracellular communication. However, signaling routes through which cells of the two generations communicate are unclear. We report that symplastic signals through plasmodesmata (PDs) of integuments are critical for the development of female gametophytes. Genetic interferences of PD biogenesis either by functional loss of CHOLINE TRANSPORTER‐LIKE1 (CTL1) or by integument‐specific expression of a mutated CALLOSE SYNTHASE 3 (cals3m) compromised PD formation in integuments and reduced fertility. Close examination of pINO:cals3m or ctl1 ovules indicated that female gametophytic development was either arrested at various stages after the formation of functional megaspores. In both cases, defective ovules could not attract pollen tubes, leading to the failure of fertilization. Results presented here demonstrate a key role of the symplastic route in sporophytic control of female gametophytic development. Significance Statement: By examining a mutant defective in plasmadesmata (PDs) formation and by genetically interfering with PD formation specifically in integuments, this study demonstrates a key role of PD in integument‐mediated female gametophytic development, implying the involvement of syplasmic transport in this process. [ABSTRACT FROM AUTHOR]

Callose contributes to many biological processes of higher plants including pollen development, cell plate and vascular tissue formation, as well as regulating the transport function of plasmodesmata. The functions of callose synthase genes in maize have been little studied. We describe a maize male-sterile mutant 39 (ms39) characterized by reduced plant height. In this study, we confirmed using CRISPR/Cas9 technology that a mutation in Zm00001d043909 (ZmCals12), encoding a callose synthase, is responsible for the male sterility of the ms39 mutant. Compared with male-fertile plants, callose deposition around the dyads and tetrads in ms39 anthers was significantly reduced. Increased cell autophagy observed in ms39 anthers may have been due to the premature programmed cell death of tapetal cells, leading to collapse of the anther wall structure. Disordered glucose metabolism in ms39 may have intensified autophagy in anthers. Evaluation of the ms39 gene on maize heterosis by paired-crossed experiment with 11 maize inbred lines indicated that ms39 can be used for maize hybrid seed production.

Callose is an important polysaccharide composed of beta-1,3-glucans and is widely implicated in plant development and defense responses. Callose synthesis is mainly catalyzed by a family of callose synthases, also known as glucan synthase-like (GSL) enzymes. Despite the fact that GSL family genes were studied in a few plant species, their functional roles have not been fully understood in woody perennials. In this study, we identified total of 84 GSL genes in seven plant species and classified them into six phylogenetic clades. An evolutionary analysis revealed different modes of duplication driving the expansion of GSL family genes in monocot and dicot species, with strong purifying selection constraining the protein evolution. We further examined the gene structure, protein sequences, and physiochemical properties of 11 GSL enzymes in Prunus mume and observed strong sequence conservation within the functional domain of PmGSL proteins. However, the exon–intron distribution and protein motif composition are less conservative among PmGSL genes. With a promoter analysis, we detected abundant hormonal responsive cis-acting elements and we inferred the putative transcription factors regulating PmGSLs. To further understand the function of GSL family genes, we analyzed their expression patterns across different tissues, and during the process of floral bud development, pathogen infection, and hormonal responses in Prunus species and identified multiple GSL gene members possibly implicated in the callose deposition associated with bud dormancy cycling, pathogen infection, and hormone signaling. In summary, our study provides a comprehensive understanding of GSL family genes in Prunus species and has laid the foundation for future functional research of callose synthase genes in perennial trees.

Callose, mainly deposited at the cell plate and in the newly formed cell wall at a very low level, is critical for cell activity and growth in plants. The genetic control and function of callose synthases, responsible for the synthesis of callose, are largely unknown in maize. In this study, we cloned a maize callose synthase, SLM1 (Seedling Lethal Mutant1) encoding for a GLUCAN SYNTHASE-LIKE (GSL) gene, from a seedling lethal mutant. Three different point mutations confirmed the key role of SLM1 to maintain maize normal growth. SLM1 was specifically expressed in immature leaf vascular with an enrichment in phloem of developing vasculature. Consistently, slm1 had severe defects in vasculature and leaf development, and terminated growth about 2 weeks after germination. Thus, SLM1 is a key gene to maintain normal growth by controlling leaf vascular development and cell activities. Loss of SLM1 function interrupted severely the important signaling pathways in which cell cyclin and histone related genes are involved. Our study reveals the critical function of a maize GSL gene and also its downstream signaling to maintain a normal growth of maize. [ABSTRACT FROM AUTHOR]

Copyright of Acta Agronomica Sinica is the property of Crop Science Society of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Key message: The article concerns the association between callose synthase and cytoskeleton by biochemical and ultrastructural analyses in the pollen tube. Results confirmed this association and immunogold labeling showed a colocalization. Callose is a cell wall polysaccharide involved in fundamental biological processes, from plant development to the response to abiotic and biotic stress. To gain insight into the deposition pattern of callose, it is important to know how the enzyme callose synthase is regulated through the interaction with the vesicle-cytoskeletal system. Actin filaments likely determine the long-range distribution of callose synthase through transport vesicles but the spatial/biochemical relationships between callose synthase and microtubules are poorly understood, although experimental evidence supports the association between callose synthase and tubulin. In this manuscript, we further investigated the association between callose synthase and microtubules through biochemical and ultrastructural analyses in the pollen tube model system, where callose is an essential component of the cell wall. Results by native 2-D electrophoresis, isolation of callose synthase complex and far-western blot confirmed that callose synthase is associated with tubulin and can therefore interface with cortical microtubules. In contrast, actin and sucrose synthase were not permanently associated with callose synthase. Immunogold labeling showed colocalization between the enzyme and microtubules, occasionally mediated by vesicles. Overall, the data indicate that pollen tube callose synthase exerts its activity in cooperation with the microtubular cytoskeleton. [ABSTRACT FROM AUTHOR]

The two main glucan polymers cellulose and callose in plant cell wall are synthesized at the plasma membrane by cellulose or callose synthase complexes. Cellulose is the prevalent glucan in cell wall and provides strength to the walls to support directed cell expansion. By contrast, callose is mainly produced in special cell wall and exercises important functions during development and stress responses. However, the structure and precise regulatory mechanism of callose synthase complex is not very clear. This review therefore compares and analyzes the regulation of callose and cellulose synthesis, and further emphasize the future research direction of callose synthesis.

Callose deposition occurs during plant growth and development, as well as when plants are under biotic and abiotic stress. Callose synthase is a key enzyme for the synthesis of callose. In this study, 27, 28, 16, and 15 callose synthase family members were identified in Gossypium hirsutum, Gossypium barbadense, Gossypium raimondii, and Gossypium arboreum using the sequence of Arabidopsis callose synthase. The CalSs were divided into five groups by phylogenetic, gene structure, and conservative motif analysis. The conserved motifs and gene structures of CalSs in each group were highly similar. Based on the analysis of cis-acting elements, it is inferred that GhCalSs were regulated by abiotic stress.WGD/Segmental duplication promoted the amplification of theCalS gene in cotton, and purification selection had an important function in the CalS family. The transcriptome data and qRT-PCR under cold, heat, salt, and PEG treatments showed that GhCalSs were involved in abiotic stress. The expression patterns of GhCalSs were different in various tissues. We predicted that GhCalS4, which was highly expressed in fibers, had an important effect on fiber elongation. Hence, these results help us understand the role of GhCalSs in fiber development and stress response. [ABSTRACT FROM AUTHOR]

Plasmodesmata (PD) are membrane-lined pores that connect adjacent cells to mediate symplastic communication in plants. These intercellular channels enable cell-to-cell trafficking of various molecules essential for plant development and stress responses, but they can also be utilized by pathogens to facilitate their infection of hosts. Some pathogens or their effectors are able to spread through the PD by modifying their permeability. Yet plants have developed various corresponding defense mechanisms, including the regulation of PD to impede the spread of invading pathogens. In this review, we aim to illuminate the various roles of PD in the interactions between pathogens and plants during the infection process. We summarize the pathogenic infections involving PD and how the PD could be modified by pathogens or hosts. Furthermore, we propose several hypothesized and promising strategies for enhancing the disease resistance of host plants by the appropriate modulation of callose deposition and plasmodesmal permeability based on current knowledge.

Plasmodesmata (PD) are membrane-lined pores that connect adjacent cells to mediate symplastic communication in plants. These intercellular channels enable cell-to-cell trafficking of various molecules essential for plant development and stress responses, but they can also be utilized by pathogens to facilitate their infection of hosts. Some pathogens or their effectors are able to spread through the PD by modifying their permeability. Yet plants have developed various corresponding defense mechanisms, including the regulation of PD to impede the spread of invading pathogens. In this review, we aim to illuminate the various roles of PD in the interactions between pathogens and plants during the infection process. We summarize the pathogenic infections involving PD and how the PD could be modified by pathogens or hosts. Furthermore, we propose several hypothesized and promising strategies for enhancing the disease resistance of host plants by the appropriate modulation of callose deposition and plasmodesmal permeability based on current knowledge. [ABSTRACT FROM AUTHOR]

Callose, a linear (1,3)-β-glucan, is an indispensable carbohydrate polymer required for plant growth and development. Advances in biochemical, genetic, and genomic tools, along with specific antibodies, have significantly enhanced our understanding of callose biosynthesis. As additional components of the callose synthase machinery emerge, the elucidation of molecular biosynthetic mechanisms is expected to follow. Short-term objectives involve defining the stoichiometry and turnover rates of callose synthase subunits. Long-term goals include generating recombinant callose synthases to elucidate their biochemical properties and molecular mechanisms, potentially culminating in the determination of callose synthase three-dimensional structure. This review delves into the structures and intricate molecular processes underlying callose biosynthesis, emphasizing regulatory elements and assembly mechanisms. [Display omitted] • Highlighting the critical role of callose biosynthesis in plant growth and defense. • Reviewing the composition of callose synthase complexes and the current understanding of callose assembly mechanisms. • Exploring genes encoding callose synthase and regulatory elements across various plant developmental stages. [ABSTRACT FROM AUTHOR]

Abiotic stress affects plants' growth and development. Soybean is an important crop of the world, however, its production is affected by abiotic stresses. Callose Synthase is the most crucial enzyme response to environmental and developmental signals. However, in soybean, information on the callose synthase genes is limited. In this study, we analyzed the callose synthase gene family of soybean at the genome-wide scale. We also studied the genes positions, gene structure, evolutionary relations, miRNAs target sites, and expression of CalS genes. Resultantly 24 CalS genes were found in soybean, with diverse chromosomal locations, cis -acting elements, conserved motifs, and gene structures. Further, GmCalS genes were divided into four phylogenetic classes. The evolutionary classification of CalSs was supported by the motif and gene structure analyses. Phytohormones, abiotic stresses, and growth-responsive elements were identified in the promoter of GmCalSs. In addition, the GmCalS genes higher expression in roots, leaves, flowers, and nodules tissues provided their significance in development. Furthermore, the higher expression of GmCalS17 and GmCalS19 genes in response to salt stress indicated their importance against salt stress. These findings will be helpful for further investigation of the CalS genes in other crops. [ABSTRACT FROM AUTHOR]

The intercellular transport of sugars, nutrients, and small molecules is essential for plant growth, development, and adaptation to environmental changes. Various stresses are known to affect the cell-to-cell molecular trafficking modulated by plasmodesmal permeability. However, the mechanisms of plasmodesmata modification and molecules involved in the phloem unloading process under stress are still not well understood. Here, we show that heat stress reduces the root meristem size and inhibits phloem unloading by inducing callose accumulation at plasmodesmata that connect the sieve element and phloem pole pericycle. Furthermore, we identify the loss-of-function of CALLOSE SYNTHASE 8 (CalS8), which is expressed specifically in the phloem pole pericycle, decreasing the plasmodesmal callose deposition at the interface between the sieve element and phloem pole pericycle and alleviating the suppression at root meristem size by heat stress. Our studies indicate the involvement of callose in the interaction between root meristem growth and heat stress and show that CalS8 negatively regulates the thermotolerance of Arabidopsis roots.

Elevated CO2 can alter plant resistance against insect herbivores. In this study, we investigated the effect of elevated CO2 on the callose synthesis involved in the resistance of Phaseolus vulgaris against Frankliniella occidentalis, which is one of the most important invasive insect pests worldwide. Elevated CO2 elevated the silver damage, callose deposition, and the expression level of CalS3 and CalS10 genes involved in callose synthase (CalS) in thrips-infested bean leaves, while reducing PR2 gene expression related to the hydrolysis of callose. In addition, both infestation by thrips and mechanical damage increased the callose deposition in leaves and induced CalS and β-1,3-glucanases (BG) expression at both transcriptional and translational levels. Under ambient CO2, callose content in the mechanically damaged plants (MDPs) and thrips-infested plants (TIPs) was positively correlated with CalS activity and the expression level of CalS3 and CalS10; BG activity was positively correlated with PR2 gene expression. Under elevated CO2, callose content in MDPs and TIPs was negatively correlated with BG activity which also negatively correlated with the expression level of CalS10 and PR2. F. occidentalis feeding can induce callose synthesis and deposition in P. vulgaris leaves, especially under elevated CO2. Specifically, genes associated with CalS defense are up-regulated, while the expression level of PR2 gene is downregulated. These results suggest that elevated CO2 can modulate callose synthesis leading to a higher level of resistance in host plants against thrips infestation. [ABSTRACT FROM AUTHOR]

Abstract Wheat is grown on more land than any other crop in the world. Current estimates suggest that yields will have to increase sixty percent by 2050 to meet the demand of an ever‐increasing human population; however, recent wheat yield gains have lagged behind other major crops such as rice and maize. One of the reasons suggested for the lag in yield potential is the lack of a robust hybrid system to harness the potential yield gains associated with heterosis, also known as hybrid vigor. Here, we set out to identify candidate genes for a genic hybrid system in wheat and characterize their function in wheat using RNASeq on stamens and carpels undergoing meiosis. Twelve genes were identified as potentially playing a role in pollen viability. CalS5‐ and RPG1‐like genes were identified as pre‐ and post‐meiotic genes for further characterization and to determine their role in pollen viability. It appears that all three homoeologues of both CalS5 and RPG1 are functional in wheat as all three homoeologues need to be knocked out in order to cause male sterility. However, one functional homoeologue is sufficient to maintain male fertility in wheat.

Abstract Silicon (Si) uptake by Poaceae plants has beneficial effects on herbivore defense. Increased plant physical barrier and altered herbivorous feeding behaviors are documented to reduce herbivorous arthropod feeding and contribute to enhanced plant defense. Here, we show that Si amendment to rice (Oryza sativa) plants contributes to reduced feeding in a phloem feeder, the brown planthopper (Nilaparvata lugens, BPH), through modulation of callose deposition. We associated the temporal dynamics of BPH feeding with callose deposition on sieve plates and further with callose synthase and hydrolase gene expression in plants amended with Si. Biological assays revealed that BPH feeding was lower in Si‐amended than in nonamended plants in the early stages post‐BPH infestation. Histological observation showed that BPH infestation triggered fast and strong callose deposition in Si‐amended plants compared with nonamended plants. Analysis using qRT‐PCR revealed that expression of the callose synthase gene OsGSL1 was up‐regulated more and that the callose hydrolase (β‐1,3‐glucanase) gene Gns5 was up‐regulated less in Si‐amended than in nonamended plants during the initial stages of BPH infestation. These dynamic expression levels of OsGSL1 and Gns5 in response to BPH infestation correspond to callose deposition patterns in Si‐amended versus nonamended plants. It is demonstrated here that BPH infestation triggers differential gene expression associated with callose synthesis and hydrolysis in Si‐amended and nonamended rice plants, which allows callose to be deposited more on sieve tubes and sieve tube occlusions to be maintained more thus contributing to reduced BPH feeding on Si‐amended plants.

Summary: Pathogen effectors act as disease promoting factors that target specific host proteins with roles in plant immunity. Here, we investigated the function of the RxLR3 effector of the plant‐pathogen Phytophthora brassicae.Arabidopsis plants expressing a FLAG‐RxLR3 fusion protein were used for co‐immunoprecipitation followed by liquid chromatography‐tandem mass spectrometry to identify host targets of RxLR3. Fluorescently labelled fusion proteins were used for analysis of subcellular localisation and function of RxLR3.Three closely related members of the callose synthase family, CalS1, CalS2 and CalS3, were identified as targets of RxLR3. RxLR3 co‐localised with the plasmodesmal marker protein PDLP5 (PLASMODESMATA‐LOCALISED PROTEIN 5) and with plasmodesmata‐associated deposits of the β‐1,3‐glucan polymer callose. In line with a function as an inhibitor of plasmodesmal callose synthases (CalS) enzymes, callose depositions were reduced and cell‐to‐cell trafficking was promoted in the presence of RxLR3.Plasmodesmal callose deposition in response to infection was compared with wild‐type suppressed in RxLR3‐expressing Arabidopsis lines. Our results implied a virulence function of the RxLR3 effector as a positive regulator of plasmodesmata transport and provided evidence for competition between P. brassicae and Arabidopsis for control of cell‐to‐cell trafficking. [ABSTRACT FROM AUTHOR]

Previously, it was reported that plant protoplasts isolated from Betula platyphylla (white birch) callus secreted bundles of hollow callose fibrils in acidic culture medium containing a high concentration of calcium ions (Ca2+). Here, the callose synthase was characterized from in situ and in vitro perspectives. Localization of callose synthases at the secreting site of callose fiber was indicated from in situ immunostaining observation of protoplasts. For in vitro analyses, membrane proteins were extracted from membrane fraction of protoplasts with a 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) treatment. The CHAPS extract aggregated in the presence of a high concentration of Ca2+, suggesting that Ca2+ may promote the arrangement of callose synthases in the plasma membrane. The callose synthase activity was dependent on pH and Ca2+, similar to the callose synthase of Arabidopsis thaliana. However, the synthesized fibril products were longer than those produced by callose synthases of herbaceous plants. This is the first insight into the specific properties of callose synthases of woody plants that secrete of callose hollow fibers. [ABSTRACT FROM AUTHOR]

Wheat is grown on more land than any other crop in the world. Current estimates suggest that yields will have to increase sixty percent by 2050 to meet the demand of an ever‐increasing human population; however, recent wheat yield gains have lagged behind other major crops such as rice and maize. One of the reasons suggested for the lag in yield potential is the lack of a robust hybrid system to harness the potential yield gains associated with heterosis, also known as hybrid vigor. Here, we set out to identify candidate genes for a genic hybrid system in wheat and characterize their function in wheat using RNASeq on stamens and carpels undergoing meiosis. Twelve genes were identified as potentially playing a role in pollen viability. CalS5‐ and RPG1‐like genes were identified as pre‐ and post‐meiotic genes for further characterization and to determine their role in pollen viability. It appears that all three homoeologues of both CalS5 and RPG1 are functional in wheat as all three homoeologues need to be knocked out in order to cause male sterility. However, one functional homoeologue is sufficient to maintain male fertility in wheat. [ABSTRACT FROM AUTHOR]

Plasmodesmata are channels that link adjacent cells in plant tissues through which molecular exchanges take place. They are involved in multiple processes vital to plant cells, such as responses to hormonal signaling or environmental challenges including osmotic stress, wounding and pathogen attack. Despite the importance of plasmodesmata, their proteome is not well-defined. Here, we have isolated fractions enriched in plasmodesmata from cell suspension cultures of Populus trichocarpa and identified 201 proteins that are enriched in these fractions, thereby providing further insight on the multiple functions of plasmodesmata. Proteomics analysis revealed an enrichment of proteins specifically involved in responses to stress, transport, metabolism and signal transduction. Consistent with the role of callose deposition and turnover in the closure and aperture of the plasmodesmata and our proteomic analysis, we demonstrate the enrichment of callose synthase activity in the plasmodesmata represented by several gene products. A new form of calcium-independent callose synthase activity was detected, in addition to the typical calcium-dependent enzyme activity, suggesting a role of calcium in the regulation of plasmodesmata through two forms of callose synthase activities. Our report provides the first proteomic investigation of the plasmodesmata from a tree species and the direct biochemical evidence for the occurrence of several forms of active callose synthases in these structures. Data are available via ProteomeXchange with identifier PXD010692.

Plasmodesmata are channels that link adjacent cells in plant tissues through which molecular exchanges take place. They are involved in multiple processes vital to plant cells, such as responses to hormonal signaling or environmental challenges including osmotic stress, wounding and pathogen attack. Despite the importance of plasmodesmata, their proteome is not well-defined. Here, we have isolated fractions enriched in plasmodesmata from cell suspension cultures of Populus trichocarpa and identified 201 proteins that are enriched in these fractions, thereby providing further insight on the multiple functions of plasmodesmata. Proteomics analysis revealed an enrichment of proteins specifically involved in responses to stress, transport, metabolism and signal transduction. Consistent with the role of callose deposition and turnover in the closure and aperture of the plasmodesmata and our proteomic analysis, we demonstrate the enrichment of callose synthase activity in the plasmodesmata represented by several gene products. A new form of calcium-independent callose synthase activity was detected, in addition to the typical calcium-dependent enzyme activity, suggesting a role of calcium in the regulation of plasmodesmata through two forms of callose synthase activities. Our report provides the first proteomic investigation of the plasmodesmata from a tree species and the direct biochemical evidence for the occurrence of several forms of active callose synthases in these structures. Data are available via ProteomeXchange with identifier PXD010692. [ABSTRACT FROM AUTHOR]

Silicon (Si) uptake by Poaceae plants has beneficial effects on herbivore defense. Increased plant physical barrier and altered herbivorous feeding behaviors are documented to reduce herbivorous arthropod feeding and contribute to enhanced plant defense. Here, we show that Si amendment to rice ( Oryza sativa) plants contributes to reduced feeding in a phloem feeder, the brown planthopper ( Nilaparvata lugens, BPH), through modulation of callose deposition. We associated the temporal dynamics of BPH feeding with callose deposition on sieve plates and further with callose synthase and hydrolase gene expression in plants amended with Si. Biological assays revealed that BPH feeding was lower in Si-amended than in nonamended plants in the early stages post- BPH infestation. Histological observation showed that BPH infestation triggered fast and strong callose deposition in Si-amended plants compared with nonamended plants. Analysis using qRT- PCR revealed that expression of the callose synthase gene Os GSL1 was up-regulated more and that the callose hydrolase (β-1,3-glucanase) gene Gns5 was up-regulated less in Si-amended than in nonamended plants during the initial stages of BPH infestation. These dynamic expression levels of Os GSL1 and Gns5 in response to BPH infestation correspond to callose deposition patterns in Si-amended versus nonamended plants. It is demonstrated here that BPH infestation triggers differential gene expression associated with callose synthesis and hydrolysis in Si-amended and nonamended rice plants, which allows callose to be deposited more on sieve tubes and sieve tube occlusions to be maintained more thus contributing to reduced BPH feeding on Si-amended plants. [ABSTRACT FROM AUTHOR]

Knowledge of the control and regulation of cellulose synthesis is fundamental to an understanding of plant development since cellulose is the primary structural component of plant cell walls. In vivo, the polymerization step requires a coordinated transport of substrates across membranes and relies on delicate orientations of the membrane-associated synthase complexes. Little is known about the properties of the enzyme complexes, and many questions about the biosynthesis of cell wall components at the cell surface still remain unanswered. Attempts to purify cellulose synthase from higher plants have not been successful because of the liability of enzymes upon isolation and lack of reliable in vitro assays. Membrane preparations from higher plant cells incorporate UDP-glucose into a glucan polymer, but this invariably turns out to be predominantly β -1,3-linked rather than β -1,4-linked glucans. Various hypotheses have been advanced to explain this phenomenon. One idea is that callose and cellulose-synthase systems are the same, but cell disruption activates callose synthesis preferentially. A second concept suggests that a regulatory protein as a part of the cellulose-synthase complex is rapidly degraded upon cell disruption. With new methods of enzyme isolation and analysis of the in vitro product, recent advances have been made in the isolation of an active synthase from the plasma membrane whereby cellulose synthase was separated from callose synthase.

Plant cells are separated by cellulose cell walls that impede direct cell-to-cell contact. In order to facilitate intercellular communication, plant cells develop unique cell-wall-spanning structures termed plasmodesmata (PD). PD are membranous channels that link the cytoplasm, plasma membranes, and endoplasmic reticulum of adjacent cells to provide cytoplasmic and membrane continuity for molecular trafficking. PD play important roles for the development and physiology of all plants. The structure and function of PD in the plant cell walls are highly dynamic and tightly regulated. Despite their importance, plasmodesmata are among the few plant cell organelles that remain poorly understood. The molecular properties of PD seem largely elusive or speculative. In this review, we firstly describe the general PD structure and its protein composition. We then discuss the recent progress in identification and characterization of PD-associated plant cell-wall proteins that regulate PD function, with particular emphasis on callose metabolizing and binding proteins, and protein kinases targeted to and around PD.

The ovary of rice undergoes rapid expansion immediately after fertilization, and this process determines the final sink strength potential of caryopses. To date, work on rice grain development has mainly focused on endosperm filling, whereas information on the essential elements for ovary expansion remains limited. We report here a functional analysis of the ovary expansion retarded mutant crr1 in rice. Map-based cloning revealed that CRR1 encodes a protein homologous to the Arabidopsis callose synthases At GSL8 and At GSL10. Point mutation in crr1 resulted in alternative splicing, which led to the formation of the truncated crr1 protein without the β-glucan synthase domain. Iodine staining showed that there were few starch granules and these were unevenly distributed in the pericarp of crr1, and a 5,6-carboxyfluorescein diacetate transport assay revealed that carbohydrates were less efficiently unloaded from the lateral vasculature into the developing caryopsis. CRR1 transcripts were detected in all plant organs, with the highest level found in receptacles, which are mainly composed of vascular tissues. Analysis of pCRR1:: GUS transgenic plants showed that CRR1 was specifically expressed in vascular bundle cells. Consistently, loss of function of CRR1 led to disordered patterns of vascular cells in the ovaries and receptacles of the mutant. Furthermore, a small portion of cells in the vascular bundles of crr1 showed defective cell wall formation, and callose deposition was specifically reduced at the plasmodesmata ( PD) of cells with aberrant walls. Our results suggest that CRR1 performs a pivotal role in determining initial ovary expansion in rice, possibly via the PD-mediated permeability of cell fate determinants for vascular cell differentiation. [ABSTRACT FROM AUTHOR]

Plasmodesmata are membrane-lined channels that are located in the plant cell wall and that physically interconnect the cytoplasm of adjacent cells. Operating as controllable valves, plasmodesmata regulate the symplastic trafficking of micro- and macromolecules, such as endogenous proteins (transcription factors) and RNA-based signals (mRNA, siRNA, etc.), hence mediating direct cell-to-cell communication and long distance signaling. Besides this physiological role, plasmodesmatal pores also form gateways through which viral genomes can pass, largely facilitating the pernicious spread of viral infections. Plasmodesmatal trafficking is either passive (e.g. diffusion) or active and responses both to developmental and environmental stimuli. In general, plasmodesmatal conductivity is regulated by the controlled build-up of callose at the plasmodesmatal neck, largely mediated through the antagonistic action of callose synthases (CalSs) and β-1,3-glucanases, respectively. Here, in this theory and hypothesis paper, we outline the importance of callose metabolism in PD SEL aperture control, and highlight the main molecular factors involved. In addition, we also review recent findings on other proteins that regulate symplastic PD transport, both in a developmental and stress-responsive framework, and discuss on their putative role in the modulation of PD callose turn-over. Finally, we also hypothesize on the role of structural sterols in the regulation of (PD) callose deposition and outline putative mechanisms by which this regulation may occur.

Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard et al., 2013). Calreticulin (CRT), a highly conserved Ca2+-binding protein found in all multi-cellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert et al., 2013). In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells.

Tocopherols (vitamin E) are lipid-soluble antioxidants produced by all plants and algae, and many cyanobacteria, yet their functions in these photosynthetic organisms are still not fully understood. We have previously reported that the vitamin E deficient 2 (vte2) mutant of Arabidopsis thaliana is sensitive to low temperature (LT) due to impaired transfer cell wall (TCW) development and photoassimilate export, associated with massive callose deposition in transfer cells of the phloem. To further understand the role of tocopherols in LT induced TCW development we compared global transcript profiles of vte2 and wild type leaves during LT treatment. Tocopherol deficiency had no impact on global gene expression in permissive conditions, but affected expression of 77 genes after 48 hours of LT treatment. In vte2 relative to wild type, genes related with solute transport were repressed, while those involved in various pathogen responses and cell wall modifications, such as GLUCAN SYNTHASE LIKE genes (GSL4 and GSL11), were induced. However, introduction of gsl4 or gsl11 mutations into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2. Intriguingly, introduction of a mutation of GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2. These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.

Background (1,3)-β-Glucan callose is a cell wall polymer that is involved in several fundamental biological processes, ranging from plant development to the response to abiotic and biotic stresses. Despite its importance in maintaining plant integrity and plant defence, knowledge about the regulation of callose biosynthesis at its diverse sites of action within the plant is still limited. The moderately sized family of GSL (GLUCAN SYNTHASE-LIKE) genes is predicted to encode callose synthases with a specific biological function and subcellular localization. Phosphorylation and directed translocation of callose synthases seem to be key post-translational mechanisms of enzymatic regulation, whereas transcriptional control of GSL genes might only have a minor function in response to biotic or abiotic stresses. Scope and Conclusions Among the different sites of callose biosynthesis within the plant, particular attention has been focused on the formation of callose in response to pathogen attack. Here, callose is deposited between the plasma membrane and the cell wall to act as a physical barrier to stop or slow invading pathogens. Arabidopsis (Arabidopsis thaliana) is one of the best-studied models not only for general plant defence responses but also for the regulation of pathogen-induced callose biosynthesis. Callose synthase GSL5 (GLUCAN SYNTHASE–LIKE5) has been shown to be responsible for stress-induced callose deposition. Within the last decade of research into stress-induced callose, growing evidence has been found that the timing of callose deposition in the multilayered system of plant defence responses could be the key parameter for optimal effectiveness. This timing seems to be achieved through co-ordinated transport and formation of the callose synthase complex. [ABSTRACT FROM PUBLISHER]

Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum (ER) called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard et al., 2013. Calreticulin (CRT), a highly conserved Ca2+-binding protein found in all multicellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen-fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert et al., 2013. In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells. [ABSTRACT FROM AUTHOR]

Tocopherols (vitamin E) are lipid-soluble antioxidants produced by all plants and algae, and many cyanobacteria, yet their functions in these photosynthetic organisms are still not fully understood. We have previously reported that the vitamin E deficient 2 (vte2) mutant of Arabidopsis thaliana is sensitive to low temperature (LT) due to impaired transfer cell wall (TCW) development and photoassimilate export associated with massive callose deposition in transfer cells of the phloem. To further understand the roles of tocopherols in LT induced TCW development we compared the global transcript profiles of vte2 and wild-type leaves during LT treatment. Tocopherol deficiency had no significant impact on global gene expression in permissive conditions, but significantly affected expression of 77 genes after 48 h of LT treatment. In vte2 relative to wild type, genes associated with solute transport were repressed, while those involved in various pathogen responses and cell wall modifications, including two members of callose synthase gene family, GLUCAN SYNTHASE LIKE 4 (GSL4) and GSL11, were induced. However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2. Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2. These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype. [ABSTRACT FROM AUTHOR]

Apple ( Malus × domestica) is an economically important temperate fruit-bearing crop which belongs to the family of Rosaceae and its pomaceous fruit is one of the most commonly cultivated. Several studies have demonstrated that the cell wall plays a pivotal role during flower and fruit development. It takes active part in pollen tube growth and contributes to determine the fruit firmness trait through the action of cell wall-related enzymes (i.e. polygalacturonase and pectinmethylesterase). We have investigated the expression of callose and cellulose synthase genes during flowering from tight cluster to anthesis and during early fruit development in domesticated apple. We also link the changes observed in gene expression to the profile of soluble non-structural carbohydrates at different developmental stages of flowers/fruitlets and to the qualitative results linked to wall polysaccharides' composition obtained through near-infrared spectroscopy. This work represents an important addition to the study of tree physiology with respect to the analysis of the expression of callose and cellulose synthase genes during flower and early fruit development in domesticated apple. [ABSTRACT FROM AUTHOR]

The intercellular transport of sugars, nutrients, and small molecules is essential for plant growth, development, and adaptation to environmental changes. Various stresses are known to affect the cell-to-cell molecular trafficking modulated by plasmodesmal permeability. However, the mechanisms of plasmodesmata modification and molecules involved in the phloem unloading process under stress are still not well understood. Here, we show that heat stress reduces the root meristem size and inhibits phloem unloading by inducing callose accumulation at plasmodesmata that connect the sieve element and phloem pole pericycle. Furthermore, we identify the loss-of-function of CALLOSE SYNTHASE 8 (CalS8), which is expressed specifically in the phloem pole pericycle, decreasing the plasmodesmal callose deposition at the interface between the sieve element and phloem pole pericycle and alleviating the suppression at root meristem size by heat stress. Our studies indicate the involvement of callose in the interaction between root meristem growth and heat stress and show that CalS8 negatively regulates the thermotolerance of Arabidopsis roots. [ABSTRACT FROM AUTHOR]

Callose (β-1,3-glucan) is a linear plant polysaccharide that plays an important role in different stages of individual development as well as in defense against unfavourable environmental factors. In plants, it is synthesized by callose synthases, and degraded by β-1,3-glucanases. This review summarizes the current knowledge on structure and function of callose in plant tissue as well as its importance under stress conditions. Despite the considerable progress in clarifying the role of this polysaccharide in plants that has been achieved during the last period, many questions regarding its synthesis or involvement in defense responses still remain to be solved. A more in-depth understanding of callose function in plants will require integration of different experimental approaches from the field of chemistry, cell biology, genetics as well as systemic biology. [ABSTRACT FROM AUTHOR]

Strengthening of plant cell walls at the site of fungal entry is one of the earliest plant responses to fungal pathogens. The aim of our study was to characterize the pattern of callose synthase localization and callose deposition in roots of Pinus sylvestris after infection by species of the Heterobasidion annosum s.l. complex with different host specificity: H. annosum s.s., H. parviporum and H. abietinum. To address this, sense-labelled probes and ribonuclease-treated samples were used to determine in situ hybridizations of callose synthase by FISH method. Furthermore, determination of callose accumulation within P. sylvestris cells was carried out using aniline blue. The different species of H. annosum s.l. had distinct impacts on the callose synthase staining within plant tissues. Moreover, while inoculation with strains of H. abietinum resulted in callose synthase accumulation at the point of hyphae contact with the host cell, this was not observed with the other species. A significant difference in callose synthesis localization was observed after inoculation with varied species of H. annosum s.l. as a result of the specific interactions with the host. [ABSTRACT FROM AUTHOR]

Apple proliferation (AP) represents a serious threat to several fruit-growing areas and is responsible for great economic losses. Several studies have highlighted the key role played by the cell wall in response to pathogen attack. The existence of a cell wall integrity signaling pathway which senses perturbations in the cell wall architecture upon abiotic/biotic stresses and activates specific defence responses has been widely demonstrated in plants. More recently a role played by cell wall-related genes has also been reported in plants infected by phytoplasmas. With the aim of shedding light on the cell wall response to AP disease in the economically relevant fruit-tree Malus × domestica Borkh., we investigated the expression of the cellulose (CesA) and callose synthase (CalS) genes in different organs (i.e., leaves, roots and branch phloem) of healthy and infected symptomatic outdoor-grown trees, sampled over the course of two time points (i.e., spring and autumn 2011), as well as in in vitro micropropagated control and infected plantlets. A strong up-regulation in the expression of cell wall biosynthetic genes was recorded in roots from infected trees. Secondary cell wall CesAs showed up-regulation in the phloem tissue from branches of infected plants, while either a down-regulation of some genes or no major changes were observed in the leaves. Micropropagated plantlets also showed an increase in cell wall-related genes and constitute a useful system for a general assessment of gene expression analysis upon phytoplasma infection. Finally, we also report the presence of several ‘knot’-like structures along the roots of infected apple trees and discuss the occurrence of this interesting phenotype in relation to the gene expression results and the modalities of phytoplasma diffusion. [ABSTRACT FROM AUTHOR]