Function of Non-Legume Orthologs of Legume Genes Required for Nodulation and Arbuscular Mycorrhizal Symbiosis

在自然生态系统中，许多植物能够通过与微生物共同生活在营养贫瘠的土壤上实现互利共赢，这是一个称为共生的过程的例子。丛枝菌根真菌与80%的陆地植物共生和根瘤菌与豆科植物的共生是植物根系与微生物之间最重要的两种共生作用。在AM共生中，AM真菌帮助植物吸收磷酸盐，而在豆科-根瘤菌共生中，根瘤菌固定大气中的氮供植物利用。这两个共生体在豆科植物中共享重叠的信号通路的发现表明，进化中较年轻的固氮共生体已经从古老的AM共生体获得了功能。最近，从几种豆科植物中克隆了一些豆科植物结瘤和AM共生所需的基因。有趣的是，几乎所有这些基因在多个植物分类群中都高度保守，它们假定的同源基因可以在水稻等非豆科植物中定义。这项研究试图阐明豆科植物结瘤和AM共生所需基因的非豆科同源基因的功能。具体目标是：(1)利用反向遗传学工具鉴定豆科植物结瘤和AM共生所需基因的功能；(2)利用推测的水稻同源基因来补充在结瘤和/或AM共生方面存在缺陷的豆科植物突变体；以及(3)使用水稻Affymetrix基因芯片对野生型和突变型水稻品系在AM真菌侵染下的转录谱进行比较。这项研究将阐明植物根系共生进化的遗传和分子机制。更广泛的影响：参与该项目的学生和博士后将接受植物基因组学、植物-微生物相互作用的分子生物学、进化和生物信息学领域的培训。将通过肯塔基大学的一个项目向高中生和教师进行宣传。

In natural ecosystems, many plants are able to grow on nutrient-poor soils by living together for mutual benefit with microorganisms, an example of a process called symbiosis. The symbiosis between arbuscular mycorrhizal (AM) fungi and 80% of land plants and that between rhizobia and legumes represent the two most important symbiotic interactions between plant roots and microbes. In the AM symbiosis, the AM fungi assist the plant in assimilating phosphate, whereas in the legume-rhizobia symbiosis, the rhizobia fix atmospheric nitrogen for use by the plant. The finding that the two symbioses share overlapping signaling pathways in legumes suggests that the evolutionary younger nitrogen-fixing symbiosis has acquired functions from the ancient AM symbiosis. Most recently, a number of legume genes required for nodulation and AM symbiosis were cloned from several legumes. Interestingly, nearly all these genes are highly conserved across multiple plant taxa, and their putative orthologs can be defined in non-legumes such as rice. This research seeks to elucidate the function of non-legume orthologs of legume genes required for nodulation and AM symbiosis. Specific objectives are: (1) Characterization of the function of the putative rice orthologs of legume genes required for nodulation and AM symbiosis using reverse genetics tools; (2) Complementation of the legume mutants that are defective in nodulation and/or AM symbiosis using the putative rice orthologs; and (3) Comparative transcript profiling of wild-type and mutant rice lines under the infection of AM fungi using the Rice Affymetrix GeneChip. This research will shed light on the genetic and molecular mechanisms underlying evolution of root symbioses in plants. Broader impacts: The students and postdocs working on this project will be trained in the areas of plant genomics, molecular biology of plant-microbe interactions, evolution, and bioinformatics. Outreach to high school students and teachers will be carried out through a program at the University of Kentucky.