Dissecting the journey and functions of barley smut fungus Ustilago hordei immunity-triggering effector UhAvr1 to reveal durable defense strategies in cereals

效应生物学是研究微生物病原体分泌的小蛋白，在人类/动物和植物科学中都是一个新兴的研究领域。对效应器的研究已经揭示了这些蛋白质与许多基本的宿主过程和信号通路相互作用和操纵的方式。效应器的目标是发育、蛋白质降解和基因调控，包括防御和抗性反应。因此，效应器告诉我们病原体是如何致病的，但也可以用作探针来阐明基本的生物过程。*真菌有大量的效应器，基因组测序项目揭示了这一点，但它们的输送方式、宿主细胞目标和功能在很大程度上仍不清楚。通过对几种侵染谷物的担子菌病原菌(大麦黑粉菌Ustilago hordei和相关的小麦叶锈菌Puccinia triticina)基因组序列的产生和分析，我们现在可以专注于许多预测的效应因子的功能。*我们最近在美国大麦中发现了一种效应器，当感染带有抗性基因Ruh1的大麦品种时，它会触发防御。这种无毒效应因子UhAVR1只在与宿主接触时表达，由真菌分泌，它与Ruh1的相互作用或它的作用导致局部宿主细胞死亡和对感染的免疫力。我们将Ruh1基因定位在大麦1号染色体短臂上一个约200kb的区域。*本建议旨在阐明3个基本问题：*1.UhAVR1的分泌机制和宿主细胞摄取的决定因素是什么？*2.UhAVR1在大麦细胞中的功能是什么，它是一个真正的毒力因子，它针对的是什么宿主细胞进程或蛋白质？*3.UhAVR1如何与Ruh1相互作用并引起免疫，我们能否分离Ruh1？*阐明效应递送机制、其宿主靶标(S)和防御诱导将有助于在该模型系统中进行研究，然而，经济上更重要的谷物锈病病理系统也在我们的实验室进行了研究。对于效应器传递至关重要的保守真菌成分是设计特定控制措施的主要目标，例如RNA沉默，我们已经为此制定了一种小麦抗锈病的策略。已鉴定的抗性基因可用于育种计划，寄主效应靶基因可通过基因组编辑进行修改，以获得作物持久的抗病能力，并减少对有害农药的依赖。**

Effector biology, the study of small secreted proteins from microbial pathogens, is a burgeoning research field in both human/animal and plant sciences. Studying effectors has already revealed insight into ways these proteins interact with and manipulate many basic host processes and signaling pathways. Effectors target development, protein degradation and gene regulation which include defense and resistance responses. Therefore, effectors teach us how pathogens cause disease but can also be used as probes to elucidate basic biological processes. ***Fungi have large suites of effectors, revealed by genome sequencing projects, but their mode of delivery, host cell targets and functions remain largely unknown. Having contributed to the generation and analyses of genome sequences of several cereal-infecting Basidiomycete pathogens (barley smut fungus Ustilago hordei and the related wheat leaf rust fungus Puccinia triticina), we can now focus on functions of the many predicted effectors. ***We recently identified in U. hordei an effector that triggers defense when infecting a barley cultivar with resistance gene Ruh1. This avirulence effector UhAVR1 is only expressed upon contact with the host, is secreted from the fungus, and its interaction with Ruh1 or its action leads to local host cell death and immunity to the infection. We genetically located Ruh1 on the short arm of barley chromosome 1 to a ~200-kb region. ******This proposal aims to shed light on 3 basic questions: ***1. What are the mechanisms of UhAVR1 secretion and determinants for host cell uptake? ***2. What is the function of UhAVR1 in barley cells, is it a real virulence factor, what host cell process or protein does it target? ***3. How does UhAVR1 interact with Ruh1 and cause immunity and can we isolate Ruh1? ******Elucidating mechanisms of effector delivery, identification of their host target(s) and defense elicitation in this model system will aid studying difficult, yet economically more important cereal rust pathosystems also studied in our laboratory. Conserved fungal components essential for effector delivery are prime targets for designing specific control measures such as RNA silencing for which we have developed a strategy in wheat against rusts. An identified resistance gene can be used in breeding programs and host effector target genes can be modified by genome editing to obtain durable disease resistance in crop plants and less reliance on harmful pesticides. **