Mapping of genetic host compatibility loci that promote the colonization of bacterial endophytes in maize

人类，动物和植物都有繁荣的细菌生态系统，这些细菌生活在它们内部而不会引起疾病。值得注意的是，人类拥有更多来自微生物栖息地的基因，而不是来自人类基因组本身的基因，植物中的情况可能类似。那些栖息在植物中而不引起疾病的微生物被称为内生菌。我们最近进行了最全面的地理和进化研究的细菌内生菌的不同类型的玉米（玉米）横跨中美洲到加拿大。玉米是世界上重要的作物之一，提供人类15%的热量，但对这种作物中的微生物的了解有限，即使其中一些微生物可能会产生毒素。因此，重要的是要了解导致特定内生菌在植物中茁壮成长或不茁壮成长的因素。在我们之前的研究中，我们发现一些细菌内生菌在玉米中持续存在了数千年的作物育种和美洲各地的迁移，而其他内生菌只在单一的玉米品种中定植。这些结果表明，玉米能够识别，或者接受或拒绝，特定菌株的内生菌。不幸的是，科学家对特定植物如何接受或拒绝特定内生菌知之甚少。内生菌可以被宿主植物中的不同遗传因子识别，然后被接受或排斥，和/或可以或多或少地与宿主的内部环境相容（例如，一些植物可以具有适当的营养物来喂养内生菌菌株）。该建议试图了解玉米如何在遗传水平上接受或拒绝特定的内生菌。我们将测量玉米遗传学家使用的两种类型的玉米（B73和Mo 17）中存在或不存在哪些内生菌，然后使用这些差异来定位负责接受或拒绝所选内生菌的玉米基因（QTL）。重要的是要了解作物如何能够区分引起重要作物疾病的微生物敌人，与中性或友好的微生物（如内生菌）相比-这些信息可能有助于科学家更好地了解作物疾病爆发以及如何预防它们。第二个原因是，几十年来，人们一直对使用内生菌涂覆在种子上（称为接种剂）或喷洒在作物上感兴趣，因为一些微生物可以抑制作物病害或减少对肥料的需求。无论安全与否，有机农民已经推广使用微生物作为合成农药和化肥的天然替代品。现在主要的农业生物技术公司已经把他们未来增长的一部分押在包括内生菌在内的“生物制品”的销售上。不幸的是，在过去，内生菌通常没有成功，因为它们在接种后不能在植物中持续存在;这些失败的一个原因可能是来自田间其他微生物的竞争，但另一个主要原因似乎是特定内生菌与特定作物品种的相容性差。如果研究人员能够绘制作物中内生菌相容性基因的图谱，他们就可以利用传统育种方法培育出能够接受有益内生菌的作物。事实上，之所以选择玉米作为这项基础研究的对象，而不是简单的植物，原因之一是所获得的信息可以立即转化为真实的世界应用。我的实验室在全球范围内处于进行这项研究的绝佳位置。首先，我们有一个独特的内生菌集合，我们已经在13种玉米中描述了它们的定植特征。其次，我的实验室在内生菌生物学和玉米遗传学方面都有专长，这是一个不寻常的组合。

PLAIN LANGUAGE SUMMARY (GENERAL PUBLIC)Humans, animals and plants have thriving ecosystems of bacteria that live inside them without causing disease. Remarkably, humans possess more genes from their microbial inhabits than from the human genome itself, and the situation is likely similar in plants. Microbes that inhabit plants without causing disease are called endophytes. We recently conducted the most comprehensive geographic and evolutionary study of bacterial endophytes of diverse types of corn (maize) spanning Central America to Canada. Corn is one of the world’s important crops, supplying 15% of human calories, yet there is limited knowledge about the microbes that inhabit this crop, even though some of these microbes, for example, may be producing toxins. Thus it is important to understand factors that cause particular endophytes to thrive or not within a plant. In our previous study, we discovered that some bacterial endophytes persisted in corn across thousands of years of crop breeding and migration across the Americas, whereas other endophytes colonized only a single corn variety. These results suggested that corn is able to recognize, and either accept or reject, specific strains of endophytes. Unfortunately, scientists have very little knowledge as to how specific plants accept or reject specific endophytes. Endophytes may be recognized, then accepted or rejected, by different genetic factors in the host plant and/or may be more or less compatible with the host’s internal environment (e.g. some plants may have the appropriate nutrients to feed an endophytic strain). This proposal attempts to understand how corn accepts or rejects specific endophytes at the genetic level. We will measure which endophytes are present or absent in two types of corn used by corn geneticists (B73 and Mo17), then use these differences to map the corn genes (QTLs) responsible for accepting or rejecting a selected endophyte.Why is this proposal important? It is important to understand how crops are able to distinguish between microbial enemies that cause important crop diseases, compared to neutral or friendly microbes such as endophytes – such information may help scientists better understand crop disease outbreaks and how to prevent them. The second reason, is that for decades, there has been interest in using endophytes to coat onto seeds (termed inoculants) or spray onto crops, since some microbes can suppress crop disease or reduce the need for fertilizers. Whether safe or not, organic farmers already promote the use of microbes as natural alternatives to synthetic pesticides and fertilizers. Now major agbiotech companies have staked part of their future growth on the sale of “biologicals” including endophytes. Unfortunately, in the past, endophytes have often not succeeded because they fail to persist in the plant after inoculation; one reason for these failures may be competition from other microbes in the field, but another major reason appears to be poor compatibility of a specific endophyte with a specific crop variety. If researchers can map the endophyte compatibility genes in crops, they can use traditional breeding to breed crops that will accept beneficial endophytes. In fact, one reason why corn was selected for this basic research proposal, as opposed to a simpler plant, is that the information gained can immediately translate into real world applications for corn farmers. My lab is in an excellent position globally to conduct this research. First, we have a unique collection of endophytes, and we have already characterized their colonization across 13 types of corn. Second, my Lab has expertise in both endophyte biology and corn genetics, which is an unusual combination.