Analysis of secreted protein effectors from the arbuscular mycorrhizal fungus G. intraradices

微生物病原体通常提供无数的效应蛋白来劫持其宿主的细胞程序。在这个焦点计划的前一阶段，我们开始了一个研究项目，以确定和表征真菌G。在丛枝菌根共生中可能具有的特征。我们已经证明，共生菌根真菌G。根内分泌的蛋白质，SP 7，与植物细胞核中的病程相关的转录因子ERF 19相互作用。ERF 19是高度诱导的根感染真菌病原体刺盘孢，但只有短暂的早期菌根定植。SP 7在植物中的组成型表达导致较高的菌根化，同时降低C.三叶草介导的ERF 19诱导。此外，SP 7在稻瘟病菌M.根腐病症状减弱。综上所述，这些结果表明，SP 7是一种效应，有助于建立/维持的菌根真菌在根中的生物营养状态，通过抵消早期的植物免疫反应。然而，有几个问题仍然悬而未决：SP 7是如何进入植物细胞的？ERF 19是SP 7的唯一目标吗？其他效应器是否与SP 7合作？是否存在丛枝特异性效应器？我们建议在项目的下一阶段回答这些问题。

Microbial pathogens often deliver a myriad of effector proteins to hijack the cellular program of their hosts. In the previous phase of this Focus Program, we started a research project to identify and characterize putative effectors from the fungus G. intraradices that could be featuring in the arbuscular mycorrhizal symbiosis. We have shown that the symbiotic mycorrhizal fungus G. intraradices secretes a protein, SP7, that interacts with the pathogenesis-related transcription factor ERF19 in the plant nucleus. ERF19 is highly induced in roots by infection with the fungal pathogen Colletotrichum trifolii but only transiently during early mycorrhiza colonization. SP7 constitutively expressed in planta leads to higher mycorrhization while reduces the levels of C. trifolii-mediated ERF19 induction. Furthermore, expression of SP7 in the rice blast fungus M. oryzae attenuates root decay symptoms. Taken together these results suggest that SP7 is an effector that contributes to establish/maintain the biotrophic status of arbuscular mycorrhizal fungi in roots by counteracting the early plant immune response. However, several questions are still open: How is SP7 entering the plant cell? Is ERF19 the only target of SP7? Are other effectors cooperating with SP7? Are there arbuscule-specific effectors? We propose to give answer to these questions in the next phase of the project.