Dissecting phytoplasma effector adaptation to plant targets (Bilateral BBSRC-FAPESP application)

植物原体是植物胞内细菌病原体，通过昆虫媒介传播。它们在植物和农作物中引起各种症状，如女巫扫帚（侧枝增加）和叶根病（花恢复为仍然不育的叶子）。在世界许多地区，植物原体会对作物生产产生负面影响。它们干扰了花卉的生产，降低了水果/谷物的产量，玉米、果树、葡萄藤、椰子等都存在这个问题。由于植物原体是昆虫传播的，随着气候变暖和杀虫剂的使用受到限制，它们的发生正在扩大。约翰英纳斯中心的Hogenhout （SH）小组在植物原体发病机理及其对寄主植物的影响方面取得了重大进展。该研究小组发现，植物原体产生特定的毒力蛋白（效应器），它与保守的植物蛋白相互作用，导致叶片起皱，增加侧分枝（女巫的扫帚），以及植物对植物原体昆虫载体的防御反应下调。后者导致更多的昆虫媒介将植物原体传播给其他植物。到目前为止，SH小组主要关注植物原体与模式植物拟南芥的相互作用。在这个项目中，SH小组将与巴西圣保罗大学的Spotti-Lopes （JSL）小组合作，后者研究了一种重要的玉米植物原体致病因子的生态学和流行病学。这种病原体引起玉米丛矮病，并由玉米叶蝉传播，在巴西、阿根廷和墨西哥的玉米地里大量繁殖，从而引发严重的植物原体流行。玉米丛矮植原体和玉米叶蝉是随着玉米从其野生祖先大刍动物驯化而共同进化的，因此它们很好地适应了玉米的殖民。植物原体感染的玉米植株通常会产生更多的初级和次级侧枝（因此被称为玉米灌木矮植原体），穗数减少，籽粒产量降低。这些受感染的植株可能支持大量的玉米叶蝉，这些叶蝉将玉米丛矮植原体传播给其他玉米植株。SH和JSL小组将共同将植物原体-拟南芥系统的知识转化为玉米丛矮植原体和玉米叶蝉的研究。更具体地说，我们将确定玉米丛矮植原体效应蛋白是否诱导了植物原体感染玉米中典型的分枝增加和减产症状。此外，我们将确定该效应剂抑制植物对玉米叶蝉的免疫，导致更大的叶蝉种群。我们还将研究巴西玉米丛矮植物原体的基因组变异。最后，我们将评估我们是否能够培育出不受植原体效应蛋白靶向的玉米品种，从而在植原体流行期间减少玉米丛矮症并增加粮食产量。我们将与农业公司陶氏农业科学公司合作。该项目将为所有参与的员工提供交流访问和学习平台。总的来说，这项工作将增加我们对病原体毒力因子（效应物）如何适应宿主目标的基本理解，从而促进病原体在这些宿主中的定植和病原体通过昆虫媒介传播。

Phytoplasmas are intracellular bacterial pathogens of plants that are transmitted by insect vectors. They induce a variety of symptoms in plants and crops, such as witches' brooms (increased lateral branching) and phyllody (flowers reverting into leaves that remain sterile). Phytoplasmas can negatively impact crop production in many regions of the world. They interfere with flower production and decline fruit/grain yields, a problem in maize, fruit trees, grapevines, coconut etc. Because phytoplasmas are insect-transmitted, their occurrence is expanding as the climate warms up and pesticide use is being restricted. The Hogenhout (SH) group at The John Innes Centre has made significant progress with phytoplasma pathogenesis and their impact on host plants. This group found that phytoplasmas produce specific virulence proteins (effectors), which interact with conserved plant proteins leading to crinkled leaves, increased lateral branching (witches' brooms) and the downregulation of plant defence responses to the phytoplasma insect vectors. The latter leads to a greater number of insect vectors that transmit the phytoplasma to other plants. So far, the SH group has focused on phytoplasma interactions with the model plant Arabidopsis thaliana. In this project, the SH group will collaborate with the Spotti-Lopes (JSL) group at The University of Sao Paulo in Brazil who has studied the ecology and epidemiology of an important phytoplasma disease agent of maize. This pathogen causes maize bushy stunt disease and is transmitted by the corn leafhopper, which builds up to high population levels in maize fields in Brazil, Argentina and Mexico, therefore triggering severe phytoplasma epidemics. Maize bushy stunt phytoplasma and the corn leafhopper have co-evolved with the domestication of maize from its wild progenitor, teosinte, and hence are well adapted to colonize maize. Phytoplasma-infected maize plants typically produce more primary and secondary lateral branches (hence, the name maize bushy stunt phytoplasma), fewer ears and lower grain yields. These infected plants may support a greater number of corn leafhoppers that transmit maize bushy stunt phytoplasma to other maize plants. Together the SH and JSL group will translate the knowledge from the phytoplasma-Arabidopsis system to investigate maize bushy stunt phytoplasma and the corn leafhopper in maize. More specifically, we will determine if a maize bushy stunt phytoplasma effector protein induces the increased branching and reduced grain yield symptoms typically observed in phytoplasma-infected maize. Moreover, we will determine of this effector suppresses plant immunity to the corn leafhopper leading to greater leafhopper populations. We will also investigate the genomic variation of maize bushy stunt phytoplasmas in Brazil. Finally, we will assess if we can generate maize varieties that are not targeted by the phytoplasma effector protein leading to a reduction in maize bushy stunt symptoms and increased grain production during phytoplasma epidemics. We will collaborate with the agricultural company Dow Agrosciences. This project will provide exchange visits and a learning platform for all staff involved. Overall this work will increase our fundamental understanding of how pathogen virulence factors (effectors) adapt to host targets thereby facilitating pathogen colonization of these hosts and pathogen dispersal by insect vectors.