Association of candidate genes with drought tolerance traits in diverse perennial ryegrass accessions
Abstract
Drought is a major environmental stress limiting growth of perennial grasses (Lolium perenne) in temperate regions. Drought tolerance is a complex trait that is controlled by multiple genes. Candidate gene association mapping provides a powerful tool for dissection of complex traits. The objectives of this study were to: 1) determine the phenotypic variation of a diverse perennial ryegrass population in response to drought stress; 2) analyze genetic diversity, population structure, and relative kinship of perennial ryegrass population with 109 simple sequence repeat (SSR) markers; 3) examine candidate gene genotyping variation through exon sequencing; and 4) discover alleles associated with drought tolerance through association mapping analysis. The population panel showed significant variation in leaf wilting, leaf water content, canopy and air temperature difference, and chlorophyll fluorescence under well-watered and drought conditions across six environments. The tolerant and sensitive accessions were identified by calculated drought sensitive index (DSI). Although infection by the symbiotic fungal endophyte Neotyphodium lolii was common among the accessions, it did not appear to influence the drought tolerance profiles of the perennial ryegrass accessions. Analysis of 109 SSR markers revealed five subpopulations in the mapping panel. No obvious relative kinship was found. A total of 2,520 expression-based sequence readings were obtained for 14 candidate genes involved in antioxidant metabolism, dehydration, water movement across membrane, and signal transduction, from which 346 single nucleotide polymorphisms were identified. Five significant associations were identified between LpLEA3, encoding a putative late embryogenesis abundant group 3 protein, and leaf water content, as well as between cytosolic Cu-ZnSOD, encoding a putative cytosolic copper-zinc superoxide dismutase, and chlorophyll fluorescence under drought conditions after controlling for population structure. Significantly associated single nucleotide polymorphisms were also translated to amino acid substitutions in different genotypes. These results indicated that allelic variation in these genes might affect amino acid changes in proteins, thereby, affecting whole-plant response to drought stress in perennial ryegrass.
Degree
Ph.D.
Advisors
Jiang, Purdue University.
Subject Area
Genetics|Plant sciences
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