Pex14/17, a filamentous fungus‐specific peroxin,is required for the import of peroxisomal matrix proteins and full virulence of Magnaporthe oryzae

Peroxisomes are ubiquitous organelles in eukaryotic cells that fulfil a variety of biochemical functions. The biogenesis of peroxisomes requires a variety of proteins, named peroxins, which are encoded by PEX genes. Pex14/17 is a putative recently identified peroxin, specifically present in filamentous fungal species. Its function in peroxisomal biogenesis is still obscure and its roles in fungal pathogenicity have not yet been documented. Here, we demonstrate the contributions of Pex14/17 in the rice blast fungus Magnaporthe oryzae (Mopex14/17) to peroxisomal biogenesis and fungal pathogenicity by targeting gene replacement strategies. Mopex14/17 has properties of both Pex14 and Pex17 with regard to its protein sequence. Mopex14/17 is distributed at the peroxisomal membrane and is essential for efficient peroxisomal targeting of proteins containing peroxisomal targeting signal 1. MoPEX19 deletion leads to the cytoplasmic distribution of Mopex14/17, indicating that the peroxisomal import of Pex14/17 is dependent on Pex19. The knockout mutants of MoPEX14/17 show reduced fatty acid utilization, reactive oxygen species (ROS) degradation and cell wall integrity. Moreover, Δmopex14/17 mutants show delayed conidial generation and appressorial formation, and a reduction in appressorial turgor accumulation and penetration ability in host plants. These defects result in a significant reduction in the virulence of the mutant. These data indicate that MoPEX14/17 plays a crucial role in peroxisome biogenesis and contributes to fungal development and pathogenicity.     

云南两个县陆稻稻瘟病菌稻巨座壳交配型测定及致病性分析

2014年,自云南省沧源县及耿马县陆稻地方品种上分离99个稻瘟病菌稻巨座壳单孢菌株,采用4个已知交配型的标准菌株对其进行育性和交配型测定.结果 表明,两地稻巨座壳菌株具较高的育性,平均可交配率高达90.8％,且可育菌株中,MAT1-1和MAT1-2菌株分别占60.9％和39.1％;分别随机对沧源县南撒村和班考村同一田块...     

壳寡糖诱导水稻过敏性细胞死亡及抗病性的提高

作为真菌细胞壁的主要成分之一的壳寡糖(Oligo-GlcNAc)能够诱导水稻悬浮细胞和幼叶细胞发生过敏性死亡,并伴有H2O2的积累.以1 μg*mL-1壳寡糖处理水稻悬浮细胞12 h后细胞明显死亡;诱导水稻幼叶细胞出现明显的死亡所需壳寡糖浓度为5 μg*mL-1.以壳寡糖处理的水稻抗稻瘟病性也明显增强.     

Pathogenicity of the rice root nematode,Hirschmanniella oryzae to rice plants in relation to nematode reproduction,plant growth,grain yield and biochemical changes

Influence of different inoculum levels of 0, 10, 100, 1000 and 10,000 individuals of Hirschmanniella oryzae on nematode reproduction and plant growth of rice cv. Giza171 and biochemical changes of infected plants was studied under screen-house conditions. Rate of nematode build up (P_f/P_i) was negatively correlated with the progressive increase in nematode inoculum levels. The percentage reduction in growth parameters, rice grain yield and the amount of total and reducing sugars were markedly affected showing a negative correlation with the tested inocula. The conspicuous reductions of plant growth, yield and total and reducing sugar contents were obtained by using 1000 and 10,000 nematodes per pot. The inoculum level of 1000 nematodes per pot was identified as critical population at which control programme must be started.     

水稻OsERF96应答病原菌的表达及启动子的功能分析

前人研究发现水稻Os ERF96(ethylene responsive factor 96)可应答白叶枯病病原菌的侵染,但其功能及表达调控机制仍不清楚,本研究进一步分析了该基因在水稻应答稻瘟病病原菌侵染及外源激素(SA和Me JA)处理下的转录情况,并分析了其启动子的诱导表达活性。结果表明:相对于对照组,Os ERF96在接种稻瘟病后1~4 d表达量显著上调,以第1天最高,此后逐渐下降,外源SA处理后Os ERF96表达量持续上调;利用Os ERF96启动子驱动GUS的转基因株系分析了Os ERF96启动子的诱导活性,结果表明GUS在根、茎和叶均有不同程度组成型表达,稻瘟病菌接种后4~7 d GUS活性持续升高。GUS活性定量表明,稻瘟病菌和SA处理条件下均出现了升高。综上所述,Os ERF96可应答白叶枯病或稻瘟病病原菌的浸染,其启动子是一个对病原菌侵染产生应答的诱导性启动子。     

Epigenetic regulation of development and pathogenesis in fungal plant pathogens

Evidently, epigenetics is at forefront in explaining the mechanisms underlying the success of human pathogens and in the identification of pathogen‐induced modifications within host plants. However, there is a lack of studies highlighting the role of epigenetics in the modulation of the growth and pathogenicity of fungal plant pathogens. In this review, we attempt to highlight and discuss the role of epigenetics in the regulation of the growth and pathogenicity of fungal phytopathogens using Magnaporthe oryzae, a devastating fungal plant pathogen, as a model system. With the perspective of wide application in the understanding of the development, pathogenesis and control of other fungal pathogens, we attempt to provide a synthesized view of the epigenetic studies conducted on M. oryzae to date. First, we discuss the mechanisms of epigenetic modifications in M. oryzae and their impact on fungal development and pathogenicity. Second, we highlight the unexplored epigenetic mechanisms and areas of research that should be considered in the near future to construct a holistic view of epigenetic functioning in M. oryzae and other fungal plant pathogens. Importantly, the development of a complete understanding of the modulation of epigenetic regulation in fungal pathogens can help in the identification of target points to combat fungal pathogenesis.     

Disruption of actin motor function due to MoMyo5 mutation impairs host penetration and pathogenicity in Magnaporthe oryzae

Actin motor myosin proteins are the driving forces behind the active transport of vesicles, and more than 20 classes of myosin have been found to contribute to a wide range of cellular processes, including endocytosis and exocytosis, autophagy, cytokinesis and the actin cytoskeleton. In Saccharomyces cerevisiae, class V myosin Myo2 (ScMyo2p) is important for the transport of distinct sets of cargo to regions of the cell along the cytoskeleton for polarized growth. To study whether myosins play a role in the formation or function of the appressorium (infectious structure) of the rice blast fungus Magnaporthe oryzae, we identified MoMyo5 as an orthologue of ScMyo2p and characterized its function. Targeted gene disruption revealed that MoMyo5 is required for intracellular transport and is essential for hyphal growth and asexual reproduction. Although the ΔMomyo5 mutant could form appressorium‐like structures, the structures were unable to penetrate host cells and were therefore non‐pathogenic. We further found that MoMyo5 moves dynamically from the cytoplasm to the hyphal tip, where it interacts with MoSec4, a Rab GTPase involved in secretory transport, hyphal growth and fungal pathogenicity. Our studies indicate that class V myosin and its translocation are tightly coupled with hyphal growth, asexual reproduction, appressorium function and pathogenicity in the rice blast fungus.     

Alpha-picolinic acid, a fungal toxin and mammal apoptosis-inducing agent, elicits hypersensitive-like response and enhances disease resistance in rice

Alpha-picolinic acid (PA), a metabolite of tryptophan and an inducer of apoptosis in the animal cell, has been reported to be a toxin produced by some of plant fungal pathogens and used in screening for disease resistant mutants. Here, we report that PA is an efficient apoptosis agent triggering cell death of hypersensitive-like response in planta. Confirmed by Fluorescence Activated Cell Sorter (FACS), rice suspension cells and leaves exhibited programmed cell death induced by PA. The PA-induced cell death was associated with the accumulation of reactive oxygen species that could be blocked by diphenylene iodonium chloride, indicating that the generation of reactive oxygen species was NADPHoxidase dependent. We also demonstrated the induction of rice defense-related genes and subsequent resistant enhancement by PA against the rice blast fungus Magnaporthe grisea. Hence, it was concluded that the PA-stimulated defense response likely involves the onset of the hypersensitive response in rice, which also provides a simple eliciting tool for studying apoptosis in the plant cell.     

hrpD6基因决定白叶枯病菌在烟草上的过敏反应和在水稻上的致病性

【目的】白叶枯病菌hrp基因簇由包括hrpD6在内的26个hpa-hrp-hrc基因组成,与植物互作后形成Ⅲ型分泌系统(T3S),将T3S效应分子注入寄主细胞中从而决定在非寄主上的过敏反应(HR)和在水稻上的致病性。但hrpD6基因是否参与了白叶枯病菌在非寄主上的过敏反应(HR)和在水稻上的致病性(pathogenicity)还不清楚。【方法】借助同源重组方法,本研究对白叶枯病菌hrpD6基因进行了突变。【结果】PCR和Southern杂交结果显示,hrpD6基因被成功敲除。烟草上测定结果显示,hrpD6突变体ΔPhrpD6丧失了HR激发能力。致病性测定发现,ΔPhrpD6在水稻苗期不能形成水渍症状,在成株期水稻上不具有致病性,并且细菌生长能力显著下降。功能互补结果显示,hrpD6基因可恢复ΔPhrpD6在烟草上激发HR和在水稻上的致病性以及在水稻组织中的生长能力。RT-PCR结果显示,hrpD6基因的转录表达不仅受水稻诱导,而且受hrpG和hrpX基因调控。不仅如此,hrpD6基因突变还影响T3S效应分子hpa1基因的转录表达和Hpa1蛋白的分泌,暗示hrpD6基因对hpa1基因转录表达具有调控作用。【结论】hrpD6基因的缺失导致白叶枯病菌不能激发烟草产生HR和和丧失在水稻上的致病性,主要是HrpD6对hpa1基因转录表达具有调控作用,并影响T3S效应分子Hpa1的分泌。这些结果为进一步分析hrpD6是否参与T3S分泌装置的形成和调控其它hrp基因的转录表达从而决定病菌在非寄主上的HR和在水稻上的致病性,提供了科学线索。