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

通俗易懂的摘要(普通大众)人类、动物和植物都有繁盛的细菌生态系统，这些细菌生活在它们的体内，不会引起疾病。值得注意的是，人类从微生物栖息地获得的基因比从人类基因组本身获得的基因更多，植物的情况很可能也是如此。生活在植物中而不会引起疾病的微生物被称为内生菌。我们最近对横跨中美洲到加拿大的不同类型玉米(玉米)的细菌内生菌进行了最全面的地理和进化研究。玉米是世界上重要的农作物之一，提供了人类15%的卡路里，但人们对寄生在玉米上的微生物知之甚少，尽管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繁荣的因素。在我们之前的研究中，我们发现，在美洲数千年的作物育种和迁徙过程中，一些细菌内生菌在玉米中持续存在，而另一些内生菌只在一个玉米品种上定居。这些结果表明，玉米能够识别并接受或拒绝特定的内生菌菌株。不幸的是，科学家们对特定植物如何接受或拒绝特定内生菌知之甚少。内生菌可能会被寄主植物中的不同遗传因素识别、接受或拒绝，和/或可能或多或少与寄主的内部环境相适应(例如，一些植物可能有适当的营养物质来喂养内生菌株)。这一建议试图在基因水平上理解玉米如何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Mo17)中存在或不存在哪些内生菌，然后利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)。为什么这项提议很重要？与内生菌等中性或友好的微生物相比，理解作物如何能够区分导致重要作物疾病的微生物敌人是重要的，这一信息可能有助于科学家更好地了解作物病害的爆发以及如何预防它们。第二个原因是，几十年来，人们一直有兴趣使用内生菌来覆盖种子(称为接种剂)或喷洒到作物上，因为一些微生物可以抑制作物病害或减少对化肥的需求。无论安全与否，有机农场主已经在推广使用微生物作为合成杀虫剂和化肥的天然替代品。现在，大型农业生物技术公司已将其未来增长的一部分押注于包括内生菌在内的“生物制品”的销售。不幸的是，在过去，内生菌往往没有成功，因为它们在接种后未能在植物中存活；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兼容性较差。如果研究人员能够在作物中定位内生菌亲和性基因，他们就可以使用传统育种来培育能够接受有益内生菌的作物。事实上，玉米被选为这项基础研究提案的一个原因，而不是一种更简单的植物，是因为所获得的信息可以立即转化为玉米农民的现实应用。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，我们已经确定了它们在13种玉米上的定植特征。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业知识，这是一个不同寻常的组合。

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.