Functional genomic characterization of germination and early infection of wheat by the fungus Zymoseptoria tritici.

为地球上所有人提供足够的食物是21世纪人类面临的主要问题。随着地球人口超过60亿，增加水稻、小麦、香蕉等主要农作物产量的需求是切实存在的。随着人口增长到2030年预计达到90亿，这一需求将会更高。在英国，小麦是一种主要作物，2013年生产了1210万吨小麦，价值超过15亿GB。然而，由小麦发酵菌引起的真菌病，特别是小麦斑点病是限制生产的主要因素。在未经处理的试验中，平均损失20%的产量，在某些情况下，据报道田间损失50%。对这种疾病的控制可能会为英国的小麦收成带来额外的240万至600万吨，如果应用于2013年的全球小麦收成，将为粮食供应带来额外的1.4亿吨。毫无疑问，STB是对全球粮食安全的严重和直接威胁，迫切需要新的控制措施。开始侵染小麦纹枯病菌的孢子落在叶表面并萌发，开始发病过程。这之后是极化生长发育和进入叶片内部，通常在12小时内。在感病小麦品种中，在感染后两天(Dpi)，真菌已经产生侧枝，到6-8dpi时，这种侧枝已经发展成在入侵点以下的大片区域。在这个阶段，真菌还没有入侵小麦细胞，在植株上几乎没有看到明显的症状。然而，8-10dpi的症状开始出现，伴随着早期无性生殖结构的发展，植物细胞的死亡和转向寄生生长。大约14-21dpi的成熟无性孢子释放出来，这个过程又开始了。这导致了流行病感染，也是产量损失如此之高的原因之一。支持我们计划研究的假设是，破坏侵染过程中最早的事件，如小麦纹枯病菌孢子萌发、叶片穿透或初始菌丝发育，将防止感染和疾病的发生。因此，针对这些发育计划所必需的基因产品的杀菌剂开发应该提供预防疾病的化合物，从而减少产量损失。我们已经与瑞士大型农业综合企业先正达建立了合作关系，以解决我们的主要目标，即表征小麦上小麦赤霉菌感染和发病的早期事件(0-4dpi)。具体地说，我们将：(1)确定小麦Z.tritici孢子在亲和小麦品种Avalon上萌发并引发感染的基因。这将提供在疾病发生中起作用的基因目录，并将在该项目中加以描述；(2)描述小麦和小麦在早期感染期间的细胞生物学，从而将特定基因与确定的感染阶段联系起来；(3)进行生物信息学和模型评估相结合的评估，以确定参与早期感染的小麦丛枝菌基因的优先次序，以便进一步分析。这将使我们能够选择100个基因进行分析，(4)我们将确定感染期间这100个基因编码的蛋白质在真菌中的位置。然后我们将依次灭活每一个，并确定这是否会阻止感染，如果是，在什么阶段？如果缺乏一种蛋白质导致不能引起感染，那么这种蛋白质就有可能成为杀菌剂开发的靶点。这些实验结合在一起，不仅将揭示实质性的新生物学，还将识别可用于在杀菌剂发现的背景下进行合理靶标选择的蛋白质。

Providing enough food for all people on the planet is a major issue facing humanity in the 21st Century. As the Earth's population tops six billion the need to increase production of staple crops e.g. rice, wheat, banana is real. As the population grows to an anticipated nine billion by 2030 that demand will be even higher. In the UK wheat is a major crop, with 12.1 million tonnes, valued at more than £1.5 billion, produced in 2013. However, fungal disease, in particular septoria tritici blotch (STB), caused by Zymoseptoria tritici, is a major constraint on production. In untreated trials an average 20% of yield is lost, and in some cases field losses of 50% have been reported. Control of this disease could contribute an extra 2.4 - 6 million tonnes to the UK wheat harvest, and if applied to the global wheat harvest in 2013 would have delivered an extra 140 million tonnes into the food supply. There is no doubt that STB is a serious and immediate threat to global food security, and new control measures are urgently required. To initiate STB infection spores of Z. tritici alight on a leaf surface and germinate, beginning the disease process. This is followed by polarized growth development and passage into the interior of the leaf, usually within 12 hours. In susceptible wheat cultivars two days post-infection (dpi) the fungus has produced lateral branching and by 6-8 dpi this has developed to circumscribe a large area beneath the point of entry. At this stage the fungus has not yet invaded wheat cells and little evident symptomology is seen on the plant. However, 8-10 dpi symptoms begin to appear, concomitant with development of an incipient asexual reproductive structure, death of plant cells and a switch to parasitic growth. Around 14-21 dpi mature asexual spores are released, and the process starts again. This results in epidemic infections and is one reason why yield loss is so high. The hypothesis underpinning our planned research is that disruption of the very earliest events in infection e.g. Z. tritici spore germination, leaf penetration or initial hyphal development will prevent establishment of infection and initiation of disease. Thus targeting fungicide development to gene products essential for these developmental programs should deliver compounds that prevent disease and hence reduce yield loss. We have established a collaboration with Syngenta, a large Swiss based agribusiness to address our principle aim, which is to characterize the early events (0-4 dpi) in establishment of infection and initiation of disease by Z. tritici on wheat. Specifically we will: (1) Define the genes that are switched on by Z. tritici spores as they germinate on and initiate infection in the compatible wheat cultivar Avalon. This will provide a catalogue of genes that play a role in the initiation of disease, and that will be characterized in this project; (2) Characterize the cellular biology of both Z. tritici and wheat during early infection, and thus link specific genes to defined infection stages; (3) Undertake a combined bioinformatics and modelling assessment to prioritize Z. tritici genes involved in early infection for further analysis. This will allow us to select one hundred genes for analysis and (4) we will determine where the proteins encoded by the 100 genes are located within the fungus during infection. We will then inactivate each in turn and determine if this blocks infection, and if so at what stage? If lack of a protein results in the inability to cause infection then this protein has potential as a target for fungicide development.Taken together these experiments will not only reveal substantial new biology they will also identify proteins that can be utilized for rational target selection within the context of fungicide discovery.