RESEARCH-PGR: Genetics and Mechanisms of Microbe-dependent Heterosis

在玉米和许多其他作物和野生植物中，杂交品种比它们的近交系亲本品种更大、更具弹性和更高的生产力。这种现象被称为杂交优势，是现代作物育种努力的基石，对全球粮食安全具有巨大价值。尽管经过了一个多世纪的密集研究，但对杂交优势的原因仍知之甚少。最近，出现了第一个证据，表明土壤中的微生物在杂交优势中发挥着重要作用。这个项目将结合经典和前沿的科学方法，包括田间实验、微生物培养、DNA测序和先进的分子技术，如代谢蛋白质组学，更详细地研究微生物对杂交优势的贡献。具体地说，这项研究将(1)测试广泛的微生物菌株和土壤微生物群在玉米中诱导杂交活力的能力；(2)确定玉米基因组中与土壤微生物反应相关的遗传变异和区域；以及(3)在分子水平上表征自交系和杂交玉米根部微生物的行为。总之，这些结果将促进人们对土壤微生物如何、何时以及为什么影响杂交活力的了解，这可能会导致在农业和生态保护方面的应用。该项目还将通过支持两名博士后研究人员、一名博士生和两名本科生研究人员的培训来增加美国的科学劳动力。它还将支持四名高中教师参加由研究人员领导的研讨会，以了解土壤微生物和农业生态系统。该项目的动机是初步数据显示，在无菌条件下或田间土壤微生物群落减少的情况下，玉米根团的杂交优势(即杂种优势)被消除或大大降低。主要目标是确定这一现象在微生物和寄主基因类型方面的普遍性；调查依赖微生物的杂种优势的遗传结构；并表征微生物与近交系和杂交寄主相互作用的分子机制。在单一栽培和简化群落中，将对现有的玉米根部内生菌集合进行筛选，以确定其诱导玉米杂种优势的能力。在无菌和接种条件下，将通过测量一组遗传多样性的玉米杂交种及其亲本系中更好的亲本杂种优势来评估微生物诱导的杂种优势的普遍性。同样的测试群体将在田间进行抗病评分，以调查与植物免疫的相互作用。总之，这些实验将有助于阐明自交系和杂交玉米植物如何与它们的微生物邻居相互作用，以及这些相互作用如何与表型杂种优势的表达有关。

In corn and many other crop and wild plants, hybrid cultivars are larger, more resilient, and more productive than their inbred parent cultivars. This phenomenon, called hybrid vigor, is a cornerstone of modern crop breeding efforts and has immense value for global food security. Despite over a century of intensive research, the causes of hybrid vigor are still poorly understood. Recently, the first evidence has arisen that microbes in the soil play an important role in hybrid vigor. This project will investigate the microbial contribution to hybrid vigor in more detail, combining classic and cutting-edge scientific approaches, including field experiments, microbial culture, DNA sequencing, and advanced molecular techniques such as metaproteomics. Specifically, this study will (1) test a wide range of microbial strains and soil microbiomes for the ability to induce hybrid vigor in corn; (2) identify genetic variants and regions of the corn genome that are associated with responsiveness to soil microbes; and (3) characterize the behavior of microbes within the roots of inbred and hybrid corn at the molecular level. Together, the results will advance knowledge of how, when, and why soil microbes affect hybrid vigor which could potentially lead to applications in agriculture and ecological conservation. This project will also grow the American scientific workforce by supporting the training of two post-doctoral researchers, one Ph.D. student, and two undergraduate student researchers. It will also support four high-school teachers to attend researcher-led workshops to learn about soil microbes and agricultural ecosystems.This project was motivated by preliminary data showing that hybrid vigor (i.e., heterosis) of maize root mass was eliminated or greatly reduced in sterile conditions or diminished soil microbial communities in the field. The overarching goals are to determine the generality of this phenomenon with respect to the microbes and host genotypes; to investigate the genetic architecture of microbe-dependent heterosis; and to characterize molecular mechanisms of microbial interactions with inbred and hybrid hosts. An existing collection of maize root endophytes will be screened for the ability to induce maize heterosis, in monoculture and in simplified communities. Metaproteomics will be used to quantify in planta protein expression by heterosis-inducing and non-inducing bacterial strains while colonizing roots of inbred vs. hybrid hosts, while RNA-seq will be used to quantify host gene expression aboveground. The generality of microbe-induced heterosis will be assessed by measuring better-parent heterosis in a genetically diverse panel of maize hybrids and their parent lines, under sterile and inoculated conditions. Finally, a high-resolution mapping population (“IBM”) will be backcrossed to each parent line, generating a test population that will be used to map genomic loci that interact with microbes to affect phenotype when in the heterozygotic state. The same test population will be scored for disease resistance in the field to investigate the interplay with plant immunity. Together, these experiments will help clarify how inbred and hybrid maize plants interact with their microbial neighbors, and how these interactions relate to the expression of phenotypic heterosis. All data and genetic resources will be made available to the general public through long-term repositories.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.