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需澄清。通过构建马铃薯早疫病病原菌Alternaria solani的基因组文库，利用同源性PCR技术，鉴定了与还原型聚酮（polyketadie）生物合成有关的聚酮合酶（PKS），该酶可能是植物毒素茄尼吡喃酮。利用已鉴定的PKS基因在马铃薯赤星病菌中的表达，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。研究了由茄链格孢菌（Alternaria solani）产生的寄主特异性化合物交链孢酸（AA）对马铃薯质膜激酶RiCDPK的生理效应以及对番茄和马铃薯细胞过敏性死亡的影响。我们证明了马铃薯RiCDPK 2基因的Ca^2+依赖性蛋白激酶编码的融合蛋白。Rishiri是从E. coli宿主细胞，用25 μ M A.索拉尼在这项研究中，融合蛋白RiCDPK 2的激酶活性受到宿主特异性毒素（HST）AA的不同影响，并被茄吡喃酮A（非HST）抑制，两者都是由A.索拉尼此外，Ca^2+和Mg 2+可能在毒素与RiCDPK 2融合蛋白的相互作用中起重要作用。我们认为A. solani可能在侵染过程中调节RiCDPK 2激酶活性，从而抑制寄主植物与A. solani，在宿主细胞中来自致病疫霉的超敏反应抑制剂也是如此。由病原体产生的有毒化合物可以通过抑制宿主-寄生虫相互作用期间的快速过敏性细胞死亡来帮助病原体建立成功的感染。

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.