云南省烟草野火病菌毒素的致病性评价*

 主要通过对烟草野火病菌菌株（Pseudomonas syringae pv. tabaci）致病力与其粗毒素毒力的相关性的研究，评价了烟草野火病菌毒素在致病过程中的作用。结果表明：①野火菌毒素毒力与其菌株的致病力呈极显著相关性，相关系数r达0.928；②高感和中感品种K326,云85对病原菌的感病性与对菌毒素的敏感性在P<0.05的水平上有相关关系；③从病斑处可以分离到该毒素，再接种能重现野火病症状；④抑菌物质对病原菌和病菌毒素的抑制作用相一致。     

Genomic variability and plasticity of Pseudomonas causing coffee leaf spots in Minas Gerais state,Brazil

Foliar spots caused by Pseudomonas coronafaciens pv. garcae (Pcg), Pseudomonas amygdali pv. tabaci (Pat) and Pseudomonas cichorii (Pch) are major bacterial diseases that can reduce coffee production. However, little is known about the genetic diversity and molecular mechanisms underlying the pathogenicity to coffee plants of these bacteria. In this study, genome sequences of Pcg, Pat and Pch strains isolated from coffee plants in Minas Gerais state, Brazil, were used to assess their variability and plasticity, and compare their type III secretion system (T3SS) and apoplastic effector repertoires as well as tabtoxin biosynthetic/detoxification genes. Genomic diversity was found for all three phytopathogens, among which Pch possesses the highest number of exclusive proteins. The Pcg genome is the most stable whereas that of Pch is the most plastic, which is related to their host ranges. When compared with those of Pseudomonas syringae pv. tomato DC3000, hrp/hrc gene sequences are more conserved in Pcg and Pat than in Pch, which also possesses the smallest T3SS and the largest apoplastic effector repertoires. The only T3SS effector family common to all three pathogens is AvrE, suggesting that, as for other plant–Pseudomonas interactions, it may play a crucial role for pathogenicity towards coffee plants. Apoplastic proteins associated with maintaining the redox balance and degrading proteins/peptides not previously described as important in plant–bacteria interactions were found. Gain/loss of the tabtoxin biosynthetic cluster with retention of the antitoxin gene was observed, indicating that tabtoxin production is not a limiting factor for the occurrence of mixed infections.     

Spatial and temporal changes in chlorophyll fluorescence images of Nicotiana benthamiana leaves following inoculation with Pseudomonas syringae pv. tabaci

Inoculation of Nicotiana benthamiana leaves with virulent and avirulent strains of Pseudomonas syringae pv. tabaci resulted in increasing changes in F_v/F_m, and NPQ over time. Images of these chlorophyll a fluorescence measurements revealed different changes in different zones of the leaf. For the virulent strain, the infiltrated zone and zone directly surrounding it showed decreased F_v/F_m, and NPQ before the appearance of visible symptoms, and these decreases corresponded with increasing bacterial populations and putative tabtoxin activity. Another distinct zone of reduced F_v/F_m and NPQ extended several centimetres from the lesion to the nearest leaf margin, but only very low bacterial populations and no putative tabtoxin activity were detected in this zone. For the avirulent strain, a hypersensitive response occurred, bacterial populations remained low, and there was little detectable putative tabtoxin activity. Decreased F_v/F_m and NPQ, but not , were observed in the infiltrated zone prior to the hypersensitive response, followed by decreased values in a zone directly surrounding it. Following that, no further changes were observed. These results demonstrate that in addition to detecting pre‐symptomatic impacts of bacteria, chlorophyll a fluorescence imaging can also show that there are highly distinct regions of affected tissue that can extend considerably beyond the area of bacterial colonization. This should be considered in selecting leaf tissues for examining the effects of pathogens on plants, such as altered host gene expression or protein levels.     

Chlorosis-inducing Phytotoxins Produced by Pseudomonas syringae

Pseudomonas syringae causes a wide range of symptoms on plants including blights, leaf spots, and galls. Phytotoxins generally enhance the virulence of phytopathogenic P. syringae, and their synthesis can substantially increase disease severity. Although several P. syringae phytotoxins cause chlorosis (coronatine, phaseolotoxin, and tabtoxin), they are synthesized by unrelated biosynthetic pathways and have completely different modes of action. Phaseolotoxin and tabtoxin inhibit ornithine carbamoyltransferase and glutamine synthetase, respectively, whereas coronatine functions as a mimic of methyl jasmonate in some plant species. This review focusses on the mode of action, genetics, biosynthesis and regulation of coronatine, tabtoxin, and phaseolotoxin. Current techniques used to detect these toxins and phytotoxin-producing P. syringae pathovars are discussed. The utilization of toxin resistance genes in the development of transgenic plants with phytotoxin tolerance is also reviewed.     

烟草野火菌毒素致病作用的研究进展

 烟草野火病是一种世界普遍发生的病害。烟草野火病菌毒素是一种重要的致病因子，从该毒素的结构，合成，致病机制及研究现状等方面概述了其在致病过程中的作用。     

烟草野火病毒素对烟草叶片组织超微结构的影响

 把用毒素处理过的叶片组织和正常叶片组织做成超薄切片,在电子显微镜下观察毒素对烟草叶细胞超微结构的影响。结果表明:毒素导致叶绿体内膜系统破坏,基粒片层解体,叶绿体形成泡囊;淀粉粒增多并膨大,连成淀粉区;细胞壁扭曲变形或断裂;细胞壁附近密集电子沉淀物。