Deciphering the fungal immune response: global gene regulation governed by the Fusarium graminearum mRNA-binding protein CSX1 in response to virus infection.

申请人的工作涉及禾谷镰刀菌的感染生物学，这是全世界小谷物上最具破坏性的植物病原体之一。每年由镰刀菌感染造成的经济损失高达数十亿欧元。拟议的项目涉及真菌病毒FGV-CH9与禾谷镰刀菌的相互作用。菌丝体感染病毒使真菌在营养生长、有性繁殖和无性繁殖以及毒力方面受到损害。这些表型与禾谷镰刀菌中mRNA稳定蛋白CSX1遗传失活后观察到的表型高度一致。转录分析进一步证实了病毒感染与CSX1之间的功能联系：病毒感染导致CSX1表达急剧下调，而CSX1的结构性表达阻止了病毒感染后症状的发展。由此可见，CSX1的表达水平决定了真菌的适合性。因此，病毒触发的CSX1下调可能代表了这种真菌的一种新的、尚未描述的免疫反应。为了验证这一假设，申请人计划通过转录组测序分析感染病毒的真菌和CSX1突变体(缺失和过表达突变体)中的全球转录重排。目标是确定同样受病毒感染和CSX1缺失影响的基因。这些基因可能建立了免疫系统，随后也将在功能上进行表征。为了进一步分析CSX1在mRNA稳定调控基因中的重要性，需要用mRNA测序的方法来检测整体的mRNA衰减率。最后，应识别与CSX1结合的特定mRNA。为此，这些转录本将与CSX1共价连接，并随后进行测序。综上所述，这些实验可能证明真菌免疫系统的存在。这个新系统的基本和辅助成分将通过结合分析和转录组测序来鉴定。在真菌免疫反应调控方面的新见解将为创新的抗性育种策略铺平道路。

The work of the applicant deals with the infection biology of Fusarium graminearum, one of the most devastating plant pathogens on small grain cereals worldwide. Economic losses by Fusarium infections are running into billions Euro each year. The proposed project deals with the interaction of the mycovirus FgV-Ch9 with F. graminearum. Infection of mycelia with virus renders the fungus impaired in vegetative growth, sexual and asexual propagation, and virulence. These phenotypes share a high degree of identity with those observed after genetic inactivation of the mRNA-stabilizing protein CSX1 in F. graminearum. A functional connection between virus infection and CSX1 was further substantiated by transcription analysis: a virus infection leads to a drastic down-regulation of CSX1 whereas a constitutive expression of CSX1 prevents the development of symptoms after virus infection. It can be concluded that the expression level of CSX1 determines the fitness of the fungus. The virus-triggered down-regulation of CSX1 might, therefore, represent a novel and, as yet undescribed, immune reaction of the fungus. To verify this assumption, the applicant plans to analyze the global transcriptional rearrangements in the virus-infected fungus and the CSX1 mutants (deletion and over-expression mutants) by transcriptome sequencing. Goal is to identify genes equally affected by virus infection and CSX1 deletion. Those genes presumably build up the immune system and shall subsequently be functionally characterized as well. In order to further analyze the importance of CSX1 in terms of gene regulation by mRNA-stabilization, global mRNA-decay rates shall be assayed by use of mRNA-sequencing. Finally, specific mRNAs that are bound by CSX1 shall be identified. For this, these transcripts will be covalently linked to CSX1 and subsequently sequenced. In summary these experiments may prove the existence of a fungal immune system. Essential and auxiliary components of this novel system will be identified by binding assays and transcriptome sequencing. New insights in the regulation of fungal immune reactions will pave the way to innovative resistance breeding strategies.