Study of the role of phototoxins in toxin-induced symptom development

许多植物病原真菌产生多种植物毒素。然而，植物毒素在植物病害中的作用仍然需要澄清。通过构建马铃薯早疫病病原菌番茄赤霉（Alternaria solani）基因组DNA文库和同源性PCR，鉴定出了参与还原聚酮酮生物合成的聚酮合成酶（PKS），该酶最有可能是植物毒素茄碱酮。鉴定的PKS基因在米曲霉菌中的表达产生了一种新的吡喃酮，其结构与茄吡喃酮具有惊人的相似性。研究了番茄互花霉（Alternaria solani）产生的宿主特异性化合物互花霉酸（alternaric acid， AA）对马铃薯RiCDPK质膜激酶及番茄和马铃薯细胞超敏性死亡的生理影响。我们证明了一种由Ca^2+依赖性蛋白激酶编码的融合蛋白来自马铃薯的cv。从大肠杆菌宿主细胞中纯化的Rishiri，用25 μ m的AA刺激。在本研究中，融合蛋白RiCDPK2的激酶活性不同程度地受到寄主特异性毒素（HST） AA的影响，并受到solanapyrone A（非HST）的抑制，两者都是由茄蚜产生的。此外，从结果来看，Ca^2+和Mg2+可能在毒素与ricdpk2融合蛋白的相互作用中起重要作用。我们认为，茄茄的HST可能在侵染过程中调节RiCDPK2激酶活性，导致宿主植物与茄茄的相容相互作用中HR的抑制，以及宿主细胞中来自植毛霉的超敏反应的抑制。由病原体产生的有毒化合物可能通过抑制宿主-寄生虫相互作用过程中超敏细胞的快速死亡来帮助病原体成功建立感染。

A number of phytopathogenic fungi produce variety of phytotoxins. The role of the phytotoxins in plant diseases, however, still needs to be clarified. Construction of genomic DNA library of causal fungus of potato early blight, Alternaria solani, and homology based PCR allowed us to identify polyketide synthase (PKS) responsible for biosynthesis of reduced polyketadie, most likely phytotoxin solanapyrone. Expression of the identifed PKS gene in Asperguillus oryzae made production of a new pyrone whose structure shows striking similarity to solanapyrone.Physiological effects of alternaric acid (AA), a host-specific compound produced by Alternaria solani on a putative plasma membrane kinase of RiCDPK of potato and on hypersensitive cell death of tomato and potato cells were studied. We demonstrated that a fusion protein encoded by Ca^2+-dependent protein kinase from potato RiCDPK2 gene of cv. Rishiri, purified from E. coli host cells, was stimulated by 25 uM AA from A. solani. In this study, the kinase activity of fusion protein RiCDPK2 is differentially affected by the host-specific toxin (HST) AA and inhibited by solanapyrone A (non-HST), both produced by A. solani. Moreover, from the results, Ca^2+ and Mg2+ may play an important role in the interaction between the toxins and RiCDPK2-fusion protein. We suggest that the HST from A. solani may regulate RiCDPK2 kinase activity during the infection process, leading to the inhibition of HR in the compatible interaction between the host plant and A. solani, as does the suppressor of hypersensitivity from Phytophthom infestans in the host cells. The toxic compounds, which are produced by the pathogen, may help the pathogen establish successful infection by suppressing rapid hypersensitive cell death during the host-parasite interaction.