Testing a two phase model of broad-host range necrotrophic compatibility

这个项目主要集中在了解侵袭性强、寄主范围广的植物病原体能够在不同的植物群体上引起疾病的基本机制。重点介绍了引起大豆、向日葵、油菜、豆类等作物白霉病的真菌病原菌核盘菌。总体而言，这种农业病原体感染了600多种植物，在美国每年造成约2亿美元的经济损失。当疾病大规模爆发时，市场损失可能非常高；例如，2009年美国大豆茎腐病的爆发直接导致收成减少约5.6亿美元。在田间，由于缺乏对核盘菌有效的抗性品种以及该真菌长期存活的特性，由核盘菌引起的病害的防治具有挑战性。在佛罗里达州，绿豆、胡萝卜、十字花菜、甜椒和卷心菜作物的损失是常年令人担忧的问题。本研究旨在阐明核盘菌侵袭性所需的遗传基础机制，以及宿主对该病原菌的易感性或抗性的遗传因素。这些信息对于制定有效的疾病控制策略来对抗这种毁灭性的真菌病原体的长期目标至关重要。这项研究将对从佛罗里达大学本科生研究少数群体参与计划招募的本科生使用尖端基因组操作工具进行分子遗传技术培训产生更广泛的影响。本项目旨在阐明在广泛寄主范围内的坏死性病原体之间建立基本亲和性的因素。工作模式是，这些病原体，如核盘菌，利用两阶段策略建立基本亲和性和宿主定植。从这个模型可以得出两个假设：第一个假设是通过病原菌靶向普遍保守的宿主靶标(例如MED16)，在广泛的宿主范围内建立了基本的宿主-病原体亲和性。另一种但不是相互排斥的假说是，这些病原体已经进化并利用不同宿主的独立毒力因子和效应器来克服宿主特有的防御(如硫代葡萄糖苷)。一个基于发现的目标和两个有针对性的具体目标将检验这些假设。第一个是为从转录组数据中选择的预测的菌核菌分泌组成员创建和表型基因特异性功能丧失突变。第二个目标是研究拟南芥介体复合体亚基16(MED16)蛋白的修饰和降解途径，以了解其在广泛的寄主范围内对坏死性病原菌的敏感性和抗性中的作用。最终目的是确定MED16降解在宿主对核盘菌和其他广泛寄主范围的坏死性病原体易感性中的作用。植物对这类病原菌的抗性落后于对其他类型寄主-病原菌相互作用的了解。这些相互作用的基因复杂性是限制理解的一个主要因素。利用新的分子遗传工具和基因组资源，拟议的研究将建立对广泛宿主范围的坏死性病原体-宿主兼容性的更大机械理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project is broadly focused on understanding the fundamental mechanisms by which aggressive, broad host range plant pathogens are able to cause disease on diverse groups of plants. The specific focus is on the fungal plant pathogen Sclerotinia sclerotiorum, the cause of white mold disease in soybean, sunflower, cole crops, pulse crops and a variety of others. In total, this agricultural pathogen infects over 600 plant species and accounts for an estimated $200 million in annual economic loss in the U.S. Market losses can be extremely high when disease outbreaks occur on a large scale; the U.S. soybean stem rot outbreak in 2009, for instance, directly reduced harvests by approximately $560 million. In the field, diseases caused by S. sclerotiorum are challenging to control for the lack of resistant cultivars effective against this pathogen and the long survival properties of the fungus. In Florida, losses occurring in crops of green bean, carrot, Brassica carinata, bell pepper and cabbage are of perennial concern. This research addresses the need to elucidate the genetically based mechanisms of S. sclerotiorum that are required for its aggressiveness and the genetic factors from the host that account for susceptibility or resistance to the pathogen. This information is fundamentally important for the long-term purpose of developing effective disease control strategies against this devastating fungal pathogen. This research will have the broader impact of training undergraduates recruited from the University of Florida Undergraduate Research Minority Participation Program in molecular genetic techniques using cutting edge tools for genome manipulation. This project aims to elucidate factors that underlie the establishment of basic compatibility in broad host range necrotrophic pathogens. The working model is that these pathogens, exemplified by Sclerotinia sclerotiorum, utilize a two-phase strategy for establishing basic compatibility and host colonization. From this model two hypotheses are possible.The first hypothesis is that basic host-pathogen compatibility across a broad range of hosts is established by pathogen targeting of universally conserved host targets (e.g., MED16). The alternative, but not mutually exclusive, hypothesis is that these pathogens have evolved and utilize independent virulence factors and effectors for different hosts to overcome host-specific defenses (e.g., glucosinolates). One discovery-based and two targeted Specific Objectives will test these hypotheses. The first is to create and phenotype gene-specific loss-of-function mutations for select members of the predicted S. sclerotiorum secretome chosen from transcriptome data. The second objective is to characterize the pathway of Arabidopsis Mediator complex subunit 16 (MED16) protein modification and degradation to understand its role in broad host range necrotrophic pathogen susceptibility and resistance. The final objective is to determine the role of MED16 degradation in host susceptibility to S. sclerotiorum and other broad host range necrotrophic pathogens. Plant disease resistance to this class of pathogens lags behind the understanding of other classes of host-pathogen interactions. The genetically complex nature of these interactions is a major factor limiting understanding. Utilizing new molecular genetic tools and genomic resources, the proposed research will establish greater mechanistic understanding of broad host range necrotrophic pathogen-host compatibility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.