Exploring The Genetic Basis Of Seed Coat And Nutritional Traits In Common Bean And Maize

Common bean (Phaseolus vulgaris L.) and maize (Zea mays L.) are two crops central to indigenous America and of great global agricultural importance. However, the landraces of common bean are largely underrepresented in genebanks, and despite the importance of elements and tocochromanols to plant function and human health, there are still gaps in the understanding of the transport and accumulation of these nutrients in maize grain. Through the array of research tools offered by the field of population genomics and quantitative genetics, this dissertation works towards addressing such gaps. The genomic characterization of ~ 300 accessions of common bean from Native Seeds/SEARCH collected from southwestern US and northwestern Mexico established it as a unique and underrepresented resource that contained important genetic diversity. Five genes encoding MYB transcription factors proximal to the C locus were identified, which is a complex genomic region responsible for the primary control of seed coat patterns. An additional novel association for partial colored seed coats was identified on chromosome 10. Through genome-wide association studies (GWAS) with high density SNP set and the 1500-line Ames panel, I investigated the genetic basis of natural variation for the concentration of 11 elements in grain and identified a total of nine causal genes encoding metal chelator or transporter. Notably, two novel associations were reported between rte2 and irt1 with boron and nickel, respectively, and a potential biofortification target, nas5, was identified for both zinc and iron. Similar moderate predictive abilities (0.33-0.53) were obtained for the 11 grain elemental phenotypes with Bayesian Ridge Regression (BRR) and BayesB. However, BayesB, allowing SNPs to have large effects, had a better fit to the genetic architecture of nickel, molybdenum, and copper, thus outperforming BRR by 4-10%. Finally, through GWAS, transcriptome-wide association studies (TWAS) and expression quantitative trait locus (eQTL) mapping, 13 causal genes that were mostly under strong cis-regulatory control were identified to associate with tocochromanol levels in maize grain. Four genes were pinpointed to be associated with tocochromanol concentrations in maize grain, including vte5, dxs1, vte7, and samt. Overall, this dissertation demonstrates a multidisciplinary approach to characterize a unique common bean collection and the genetic control of its seed coat pattern, and provides a comprehensive assessment of the genetic basis of nutritional qualities in maize grain.