Callose Synthesis Research Articles

Arabidopsis Endoplasmic Reticulum-Localized UBAC2 Proteins Interact with PAMP-INDUCED COILED-COIL to Regulate Pathogen-Induced Callose Deposition and Plant Immunity.

Pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) is initiated upon PAMP recognition by pattern recognition receptors (PRR). PTI signals are transmitted through activation of mitogen-activated protein kinases (MAPKs), inducing signaling and defense processes such as reactive oxygen species (ROS) production and callose deposition. Here, we examine mutants for two Arabidopsis thaliana genes encoding homologs of UBIQUITIN-ASSOCIATED DOMAIN-CONTAINING PROTEIN 2 (UBAC2), a conserved endoplasmic reticulum (ER) protein implicated in ER protein quality control. The ubac2 mutants were hypersusceptible to a type III secretion-deficient strain of the bacterial pathogen Pseudomonas syringae, indicating a PTI defect. The ubac2 mutants showed normal PRR biogenesis, MAPK activation, ROS burst, and PTI-associated gene expression. Pathogen- and PAMP-induced callose deposition, however, was compromised in ubac2 mutants. UBAC2 proteins interact with the plant-specific long coiled-coil protein PAMP-INDUCED COILED COIL (PICC), and picc mutants were compromised in callose deposition and PTI. Compromised callose deposition in the ubac2 and picc mutants was associated with reduced accumulation of the POWDERY MILDEW RESISTANT 4 (PMR4) callose synthase, which is responsible for pathogen-induced callose synthesis. Constitutive overexpression of PMR4 restored pathogen-induced callose synthesis and PTI in the ubac2 and picc mutants. These results uncover an ER pathway involving the conserved UBAC2 and plant-specific PICC proteins that specifically regulate pathogen-induced callose deposition in plant innate immunity.

The zinc finger protein DCM1 is required for male meiotic cytokinesis by preserving callose in rice.

Meiotic cytokinesis influences the fertility and ploidy of gametes. However, limited information is available on the genetic control of meiotic cytokinesis in plants. Here, we identified a rice mutant with low male fertility, defective callose in meiosis 1 (dcm1). The pollen grains of dcm1 are proved to be defective in exine formation. Meiotic cytokinesis is disrupted in dcm1, resulting in disordered spindle orientation during meiosis II and formation of pollen grains with varied size and DNA content. We demonstrated that meiotic cytokinesis defect in dcm1 is caused by prematurely dissolution of callosic plates. Furthermore, peripheral callose surrounding the dcm1 pollen mother cells (PMCs) also disappeared untimely around pachytene. The DCM1 protein contains five tandem CCCH motifs and interacts with nuclear poly (A) binding proteins (PABNs) in nuclear speckles. The expression profiles of genes related to callose synthesis and degradation are significantly modified in dcm1. Together, we propose that DCM1 plays an essential role in male meiotic cytokinesis by preserving callose from prematurely dissolution in rice.

Rough and tough. How does silicic acid protect horsetail from fungal infection?

Horsetail (Equisetum arvense) plants grew healthily for 10 weeks under both Si-deficient and Si-replete conditions. After 10 weeks, plants grown under Si-deficient conditions succumbed to fungal infection. We have used NanoSIMS and fluorescence microscopy to investigate silica deposition in the tissues of these plants. Horsetail grown under Si-deficient conditions did not deposit identifiable amounts of silica in their tissues. Plants grown under Si-replete conditions accumulated silica throughout their tissues and especially in the epidermis of the outer side of the leaf and the furrow region of the stem where it was continuous and often, as a double layer suggestive of a barrier function. We have previously shown, both in vivo (in horsetail and thale cress) and in vitro (using an undersaturated solution of Si(OH)4), that callose is a “catalyst” of plant silica deposition. Here we support this finding by comparing the deposition of silica to that of callose and by showing that they are co-localized. We propose the existence of a synergistic mechanical protection by callose and silica against pathogens in horsetail, whereby the induction of callose synthesis and deposition is the first, biochemical line of defence and callose-induced precipitation of silica is the second, adventitious mechanical barrier.

Exocyst Subunit EXO70H4 Has a Specific Role in Callose Synthase Secretion and Silica Accumulation.

Biogenesis of the plant secondary cell wall involves many important aspects, such as phenolic compound deposition and often silica encrustation. Previously, we demonstrated the importance of the exocyst subunit EXO70H4 for biogenesis of the trichome secondary cell wall, namely for deposition of the autofluorescent and callose-rich cell wall layer. Here, we reveal that EXO70H4-driven cell wall biogenesis is constitutively active in the mature trichome, but also can be activated elsewhere upon pathogen attack, giving this study a broader significance with an overlap into phytopathology. To address the specificity of EXO70H4 among the EXO70 family, we complemented the exo70H4-1 mutant by 18 different Arabidopsis (Arabidopsis thaliana) EXO70 paralogs subcloned under the EXO70H4 promoter. Only EXO70H4 had the capacity to rescue the exo70H4-1 trichome phenotype. Callose deposition phenotype of exo70H4-1 mutant is caused by impaired secretion of PMR4, a callose synthase responsible for the synthesis of callose in the trichome. PMR4 colocalizes with EXO70H4 on plasma membrane microdomains that do not develop in the exo70H4-1 mutant. Using energy-dispersive x-ray microanalysis, we show that both EXO70H4- and PMR4-dependent callose deposition in the trichome are essential for cell wall silicification.

Callose synthesis as a factor of adult resistance of wheat to leaf rust

Callose synthesis as a factor of adult resistance of wheat to leaf rust

Silicon amendment to rice plants contributes to reduced feeding in a phloem‐sucking insect through modulation of callose deposition

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.

Regulation of Physiological and Biochemical Processes in an Intact Plant Is Determined by Interaction of Flows of Substance Bulk Transfer

The analysis of characteristic features of photosynthesis alterations, assimilate transport, growth function, and plant leaf ultrastructure under the changes in sink-source relations (SSR) between photosynthetic and sink organs is carried out, as well as the level of nitrogen (nitrate) nutrition. Under modeling conditions, there is shown NO-triggering mechanism of inhibition of assimilate export from leaves which becomes involved with the increase in the plant apoplast nitrate level. The concept that the plant metabolism regulation under the changes of environmental conditions is realized through the interaction of counter flows of nitrates and photoassimilates. This interaction involves changing in the degree of reduction of absorbed nitrates resulting in NO formation. By activating the callose synthesis, NO plugs pores in sieve tubes and inhibits sugar transport along the phloem. Numerous genes are activated under the effect of NO signal system. Out of all enzymes synthesized due to the expression of these genes, there function and change the metabolism only the ones for which cofactors and substrates resulting from SSR disturbance exist. Such reorganization of metabolism occurs every new photoperiod in accordance with new levels of assimilates and nitrates in plants.

Unravelling early events in the Taphrina deformans-Prunus persica interaction: an insight into the differential responses in resistant and susceptible genotypes.

Leaf peach curl is a devastating disease affecting leaves, flowers and fruits, caused by the dimorphic fungus Taphrina deformans. To gain insight into the mechanisms of fungus pathogenesis and plant responses, leaves of a resistant and two susceptible Prunus persica genotypes were inoculated with blastospores (yeast), and the infection was monitored during 120h post inoculation (h.p.i.). Fungal dimorphism to the filamentous form and induction of reactive oxygen species (ROS), callose synthesis, cell death and defence compound production were observed independently of the genotype. Fungal load significantly decreased after 120h.p.i. in the resistant genotype, while the pathogen tended to grow in the susceptible genotypes. Metabolic profiling revealed a biphasic re-programming of plant tissue in susceptible genotypes, with an initial stage co-incident with the yeast form of the fungus and a second when the hypha is developed. Transcriptional analysis of PRs and plant hormone-related genes indicated that pathogenesis-related (PR) proteins are involved in P.persica defence responses against T.deformans and that salicylic acid is induced in the resistant genotype. Conducted experiments allowed the elucidation of common and differential responses in susceptible versus resistant genotypes and thus allow us to construct a picture of early events during T.deformans infection.

Increased callose deposition in plants lacking DYNAMIN-RELATED PROTEIN 2B is dependent upon POWDERY MILDEW RESISTANT 4

ABSTRACTCallose deposition within the cell wall is a well-documented plant immune response to pathogenic organisms as well as to pathogen-/microbe- associated molecular patterns (P/MAMPs). However, the molecular mechanisms that modulate pathogen-induced callose deposition are less understood. We reported previously that Arabidopsis plants lacking the vesicle trafficking component DYNAMIN-RELATED PROTEIN 2B (DRP2B) display increased callose deposition in response to the PAMP flg22. Here, we show that increased number of flg22-induced callose deposits in drp2b leaves is fully dependent on the callose synthase POWDERY MILDEW RESISTANT 4 (PMR4). We propose that in addition to functioning in flg22-induced endocytosis of the plant receptor, FLAGELLIN SENSING 2, DRP2B may regulate the trafficking of proteins involved in callose synthesis, such as PMR4, and/or callose degradation.

A Strategy to Validate the Role of Callose-mediated Plasmodesmal Gating in the Tropic Response.

The plant hormone auxin plays an important role in many growth and developmental processes, including tropic responses to light and gravity. The establishment of an auxin gradient is a key event leading to phototropism and gravitropism. Previously, polar auxin transport (PAT) was shown to establish an auxin gradient in different cellular domains of plants. However, Han et al. recently demonstrated that for proper auxin gradient formation, plasmodesmal callose-mediated symplasmic connectivity between the adjacent cells is also a critical factor. In this manuscript, the strategy to elucidate the role of particular genes, which can affect phototropism and gravitropism by altering the symplasmic connectivity through modulating plasmodesmal callose synthesis, is discussed. The first step is to screen aberrant tropic responses from 3-day-old etiolated seedlings of mutants or over-expression lines of a gene along with the wild type. This preliminary screening can lead to the identification of a range of genes functioning in PAT or controlling symplasmic connectivity. The second screening involves the sorting of candidates that show altered tropic responses by affecting symplasmic connectivity. To address such candidates, the movement of a symplasmic tracer and the deposition of plasmodesmal callose were examined. This strategy would be useful to explore new candidate genes that can regulate symplasmic connectivity directly or indirectly during tropic responses and other developmental processes.

Synthesis of 4-functionalyzed 2,3-bis(diethoxyphosphorylmethyl)furans

Using alkyl 4,5-bis(diethoxyphosphorylmethyl)furan-3-carboxylate as examples, we have demonstrated the possibility of synthesis of a phosphorylated analog of aglycone of the glycoside regulator of cellulose and callose synthesis, bis(phosphorylated) furoyl derivatives of natural amino acids, and phosphorus-containing derivatives of N-furyl-N′-hydroxyethylurea; these compounds are of interest for pharmacology.

铝胁迫下胡枝子根尖胼胝质形成规律及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 铝胁迫下胡枝子根尖胼胝质形成规律及影响因素 DOI: 10.5846/stxb201406091185 作者: 作者单位: 中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室,中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室,湖北理工学院环境科学与工程学院,中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 土壤与农业可持续发展国家重点实验室开放基金课题(0812201225);湖北省自然基金面上项目(2014CFC1089);湖北省矿区环境污染控制与修复重点实验室开放基金(2013104);湖北理工学院引进人才项目(10yjz04R);国家重点基础研究发展计划项目(973项目)(2014CB441000) Analysis of variations in and factors affecting callose formation in response to al stress in Lespedeza Root Tips Author: Affiliation: State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences,State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences,College of Environmental Science and Engineering,Hubei Institute of Technology,Huangshi,State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用水培试验,研究了铝胁迫下两个胡枝子品种根尖产生胼胝质的变化规律及影响因素。结果表明,两个品种的根尖铝吸收量与胼胝质形成量呈正比例关系。品种间差异主要是在根尖0-0.5 cm处。敏感品种胼胝质形成量同铝吸收量的变化趋势相一致,而耐性品种则在铝处理6 h时出现一个高峰值后下降。去除铝胁迫后,耐性品种胼胝质形成量并不显著减少。与单独铝处理相比,阴离子通道抑制剂苯甲酰甲醛加铝处理对两个品种胼胝质形成无影响;尼氟灭酸加铝处理抑制敏感品种胼胝质的形成,对耐性品种无影响;蒽-9-羧酸加铝处理显著抑制两个品种的胼胝质形成。另外,抑制剂2-去氧-D-葡萄糖加铝共同处理与单独铝处理相比,敏感品种的胼胝质形成量显著降低,耐性品种无影响。甘露醇对两个品种胼胝质形成的影响无显著差别。镧处理下胼胝质的形成量是耐性品种显著高于敏感品种,铝、镧同时处理胼胝质的形成量最高。敏感品种胼胝质形成处理间无差别。总之,耐性品种在铝胁迫下胼胝质形成与有机酸分泌可能存在一定的协调关系;铝胁迫下胼胝质形成是敏感指标;在一定条件下,特别是有机酸分泌前胼胝质的形成可能具有一定抗性意义;铝诱导胼胝质的形成受多种外界因素(浓度、时间、有机酸分泌,渗透压等)的影响。 Abstract:Lespedeza speices can grow very well in infertile acidic soils as native pioneer plants. The reasons why such plants are well adapted to these soils might be due to a combination of mechanisms. Al toxicity is the primary factor limiting plant growth in acidic soils. Our previous results indicated that secretion of malate and citrate from roots was related to the high Al-resistance of Lespedeza. The objective of this study was to investigate the formation of callose under Al stress and its regulating factors in two Lespedeza species with different Al resistance, and attempted to explore the relative role of callose formation and organic acid exudation in Al toxicity or resistance of Lespedeza. The results showed that increased Al uptake was associated with increased callose formation in both Lespedeza species. The differences in Al tolerance between the two species were mainly expressed at the root apical 0-0.5 cm. Moreover, the callose formation was similar to root Al uptake for Al-sensitive species, but not for Al-tolerant species, of which callose formation peaked at 6 h of Al treatment and then decreased. Callose formation of the tolerant species was not obviously reduced following removal of Al from the culture. Furthermore, no obvious differences in callose formation were observed under treatment with PG (phenylglyoxal, anion-channel inhibitor) plus Al as compared to Al treatment alone in both species. NIF (niflumic acid, anion-channel inhibitor) plus Al treatment inhibited callose formation in the Al-sensitive species, but not in the Al-tolerant species. Callose formation was inhibited by A-9-C (9-anthracene carboxylic acid, anion-channel inhibitor) plus Al treatment in both species. Compared with Al treatment alone, DDG plus Al treatment caused a significant reduction in callose formation in the Al-sensitive species but not in the Al-tolerant species. No differences in callose formation were observed for both species following mannitol treatment. Callose formation in response to La treatment was significantly higher in the Al-tolerant species than in the Al-sensitive species and was still higher following treatment with both Al and La. However, no differences in callose formation in Al-sensitive species were detected among treatments. In summary, callose synthesis may be regulated in conjunction with organic acid exudation. Callose formation may be a sensitive indicator of Al stress and may also function in Al tolerance before organic acids are secreted from roots. Finally, callose formation may be dependent on many factors, including Al concentration, treatment time, organic acid exudation, and osmotic pressure. Further studies are required to examine these additional factors to determine the complex mechanisms mediating callose formation. 参考文献 相似文献 引证文献

Induction of Embryogenesis in Brassica Napus Microspores Produces a Callosic Subintinal Layer and Abnormal Cell Walls with Altered Levels of Callose and Cellulose.

The induction of microspore embryogenesis produces dramatic changes in different aspects of the cell physiology and structure. Changes at the cell wall level are among the most intriguing and poorly understood. In this work, we used high pressure freezing and freeze substitution, immunolocalization, confocal, and electron microscopy to analyze the structure and composition of the first cell walls formed during conventional Brassica napus microspore embryogenesis, and in cultures treated to alter the intracellular Ca2+ levels. Our results revealed that one of the first signs of embryogenic commitment is the formation of a callose-rich, cellulose-deficient layer beneath the intine (the subintinal layer), and of irregular, incomplete cell walls. In these events, Ca2+ may have a role. We propose that abnormal cell walls are due to a massive callose synthesis and deposition of excreted cytoplasmic material, and the parallel inhibition of cellulose synthesis. These features were absent in pollen-like structures and in microspore-derived embryos, few days after the end of the heat shock, where abnormal cell walls were no longer produced. Together, our results provide an explanation to a series of relevant aspects of microspore embryogenesis including the role of Ca2+ and the occurrence of abnormal cell walls. In addition, our discovery may be the explanation to why nuclear fusions take place during microspore embryogenesis.

Transcriptome changes associated with cold acclimation in leaves of olive tree (Olea europaea L.)

Olea europaea L. ssp. sativa is an evergreen fruit tree well adapted to the climate conditions of the Mediterranean basin. Its cultivation in northern regions may expose the plants to cold and frost damages during winter, although the maturation of olive fruit in cool environments may provide olive oil with peculiar qualitative characteristics. This work aims at studying short- and long-term transcriptional changes occurring in leaves of olive trees cv. Leccino exposed to a progressive lowering of temperatures, till −4 °C. Following a RNA-Seq analysis, a leaf transcriptome comprising 44,332 transcripts has been de novo assembled and 5464 differentially expressed genes (DEGs) identified. Transcriptomic data identified almost all the typical components of the known and conserved molecular repertoire of the plant cold response, including changes in membrane composition-related genes, induction of cold-regulated genes (cor), and transcription factors, and downregulation of photosynthesis-related genes. Besides the known components of cold response, we also identified some specific features characterizing the cold response of olive tree. Indeed, during cold acclimation, olive tree leaves induced genes of the glutathione cycle, polyamine and flavonoid pathways, likely to support reactive oxygen species (ROS) scavenging, as well as genes of the raffinose and trehalose biosynthetic pathways to sustain the accumulation of osmolytes. Further, the signaling pathway of abscisic acid (ABA) was strongly implicated, while induction of genes responsible for synthesis of callose and lignins indicated changes in composition of cell wall. In parallel to the transcriptome analysis, a CBF-like transcript has been identified and its expression profile studied in the reference cv. Leccino as well as in seven cvs. differing for cold tolerance.

Sr36- and Sr5-Mediated Resistance Response to Puccinia graminis f. sp. tritici Is Associated with Callose Deposition in Wheat Guard Cells.

Race-specific resistance of wheat to Puccinia graminis f. sp. tritici is primarily posthaustorial and often involves the induction of a hypersensitive response (HR). The aim of this study was to investigate host defense responses induced in interactions between P. graminis f. sp. tritici races and wheat lines carrying different race-specific stem rust resistance (Sr) genes. In incompatible interactions between wheat lines carrying Sr36 in three genetic backgrounds (LMPG, Prelude, or W2691) and avirulent P. graminis f. sp. tritici races MCCFC or RCCDM, callose accumulated within 24 h in wheat guard cells contacted by a P. graminis f. sp. tritici appressorium, and P. graminis f. sp. tritici ingress was inhibited following appressorium formation. Accordingly, the expression of transcripts encoding a callose synthase increased in the incompatible interaction between LMPG-Sr36 and avirulent P. graminis f. sp. tritici race MCCFC. Furthermore, the inhibition of callose synthesis through the infiltration of 2-deoxy-D-glucose (DDG) increased the ability of P. graminis f. sp. tritici race MCCFC to infect LMPG-Sr36. A similar induction of callose deposition in wheat guard cells was also observed within 24 h after inoculation (hai) with avirulent P. graminis f. sp. tritici race HKCJC on LMPG-Sr5 plants. In contrast, this defense response was not induced in incompatible interactions involving Sr6, Sr24, or Sr30. Instead, the induction of an HR and cellular lignification were noted. The manifestation of the HR and cellular lignification was induced earlier (24 hai) and was more extensive in the resistance response mediated by Sr6 compared with those mediated by Sr24 or Sr30. These results indicate that the resistance mediated by Sr36 is similar to that mediated by Sr5 but different from those triggered by Sr6, Sr24, or Sr30. Resistance responses mediated by Sr5 and Sr36 are prehaustorial, and are a result of very rapid recognition of molecules derived from avirulent isolates of P. graminis f. sp. tritici, in contrast to the responses triggered in lines with Sr6, Sr24, and Sr30.

Overexpression of AtTTP affects ARF17 expression and leads to male sterility in Arabidopsis.

Callose synthesis is critical for the formation of the pollen wall pattern. CalS5 is thought to be the major synthethase for the callose wall. In the Arabidopsis anther, ARF17 regulates the expression of CalS5 and is the target of miR160. Plants expressing miR160-resistant ARF17 (35S:5mARF17 lines) with increased ARF17 mRNA levels display male sterility. Here we report a zinc finger family gene, AtTTP, which is involved in miR160 maturation and callose synthesis in Arabidopsis. AtTTP is expressed in microsporocytes, tetrads and tapetal cells in the anther. Over-expression lines of AtTTP (AtTTP-OE line) exhibited reduced male fertility. CalS5 expression was tremendously reduced and the tetrad callose wall became much thinner in the AtTTP-OE line. Northern blotting hybridization and quantitative RT-PCR analysis revealed that miR160 was decreased, while the expression of ARF17 was increased in the AtTTP-OE line. Based on these results, we propose that AtTTP associates with miR160 in order to regulate the ARF17 expression needed for callose synthesis and pollen wall formation.

Three ancient hormonal cues co-ordinate shoot branching in a moss.

Shoot branching is a primary contributor to plant architecture, evolving independently in flowering plant sporophytes and moss gametophytes. Mechanistic understanding of branching is largely limited to flowering plants such as Arabidopsis, which have a recent evolutionary origin. We show that in gametophytic shoots of Physcomitrella, lateral branches arise by re-specification of epidermal cells into branch initials. A simple model co-ordinating the activity of leafy shoot tips can account for branching patterns, and three known and ancient hormonal regulators of sporophytic branching interact to generate the branching pattern- auxin, cytokinin and strigolactone. The mode of auxin transport required in branch patterning is a key divergence point from known sporophytic pathways. Although PIN-mediated basipetal auxin transport regulates branching patterns in flowering plants, this is not so in Physcomitrella, where bi-directional transport is required to generate realistic branching patterns. Experiments with callose synthesis inhibitors suggest plasmodesmal connectivity as a potential mechanism for transport.

A cellular backline: specialization of host membranes for defence.

In plant-pathogen interactions, the host plasma membrane serves as a defence front for pathogens that invade from the extracellular environment. As such, the lipid bilayer acts as a scaffold that targets and delivers defence responses to the site of attack. During pathogen infection, numerous changes in plasma membrane composition, organization, and structure occur. There is increasing evidence that this facilitates the execution of a variety of responses, highlighting the regulatory role membranes play in cellular responses. Membrane microdomains such as lipid rafts are hypothesized to create signalling platforms for receptor signalling in response to pathogen perception and for callose synthesis. Further, the genesis of pathogen-associated structures such as papillae and the extra-haustorial membrane necessitates polarization of membranes and membrane trafficking pathways. Unlocking the mechanisms by which this occurs will enable greater understanding of how targeted defences, some of which result in resistance, are executed. This review will survey some of the changes that occur in host membranes during pathogen attack and how these are associated with the generation of defence responses.

Relationship between male sterility and β-1,3-glucanase activity and callose deposition-related gene expression in wheat (Triticum aestivum L.).

In previous studies, we first isolated one different protein β-1,3-glucanase using two-dimensional electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry from normal wheat (Triticum aestivum L.) and chemical hybridization agent-induced male sterility (CIMS) wheat. In this experiment, β-1,3-glucanase activity and the expression of a callose deposition-related gene, UDP-glucose phosphorylase (UGPase), were determinate in normal, CIMS, and genetic male sterility (GS) wheat. β-1,3-glucanase activity was significantly different between the fertile and sterile lines during callose synthesis and degradation, but there was no difference between CIMS and GS wheat. The UGPase gene of callose deposition was highly expressed in the meiophase and sharply decreased in the tetrad stage. However, the expression of the UGPase gene was significantly different between the fertile and sterile lines. These data indicated that β-1,3-glucanase activity and the expression of the UGPase gene play important roles in the male sterility of wheat. Consequently, pollen mother cells (PMCs) might degenerate at the early meiosis stage, and differences in UGPase gene expression and β-1,3-glucanase activity might eventually result in complete pollen collapse. In addition, the critical period of anther abortion might be the meiosis stage to the tetrad stage rather than what we previously thought, the mononuclear period.

Transgenic Arabidopsis thaliana plants expressing a β-1,3-glucanase from sweet sorghum (Sorghum bicolor L.) show reduced callose deposition and increased tolerance to aluminium toxicity.

Seventy-one cultivars of sweet sorghum (Sorghum bicolor L.) were screened for aluminium (Al) tolerance by measuring relative root growth (RRG). Two contrasting cultivars, ROMA (Al tolerant) and POTCHETSTRM (Al sensitive), were selected to study shorter term responses to Al stress. POTCHETSTRM had higher callose synthase activity, lower β-1,3-glucanase activity and more callose deposition in the root apices during Al treatment compared with ROMA. We monitored the expression of 12 genes involved in callose synthesis and degradation and found that one of these, SbGlu1 (Sb03g045630.1), which encodes a β-1,3-glucanase enzyme, best explained the contrasting deposition of callose in ROMA and POTCHETSTRM during Al treatment. Full-length cDNAs of SbGlu1 was prepared from ROMA and POTCHETSTRM and expressed in Arabidopsis thaliana using the constitutive cauliflower mosaic virus (CaMV) 35S promoter. Independent transgenic lines displayed significantly greater Al tolerance than wild-type plants and vector-only controls. This phenotype was associated with greater total β-1,3-glucanase activity, less Al accumulation and reduced callose deposition in the roots. These results suggest that callose production is not just an early indicator of Al stress in plants but likely to be part of the toxicity pathway that leads to the inhibition of root growth.