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Community association populations are composed of phenotypically and genetically diverse accessions. Once these populations are genotyped, the resulting marker data can be reused by different groups investigating the genetic basis of different traits. Because the same genotypes are observed and scored for a wide range of traits in different environments, these populations represent a unique resource to investigate pleiotropy. Here, we assembled a set of 234 separate trait datasets for the Sorghum Association Panel, a group of 406 sorghum genotypes widely employed by the sorghum genetics community. Comparison of genome-wide association studies (GWAS) conducted with two independently generated marker sets for this population demonstrate that existing genetic marker sets do not saturate the genome and likely capture only 35-43% of potentially detectable loci controlling variation for traits scored in this population. While limited evidence for pleiotropy was apparent in cross-GWAS comparisons, a multivariate adaptive shrinkage approach recovered both known pleiotropic effects of existing loci and new pleiotropic effects, particularly significant impacts of known dwarfing genes on root architecture. In addition, we identified new loci with pleiotropic effects consistent with known trade-offs in sorghum development. These results demonstrate the potential for mining existing trait datasets from widely used community association populations to enable new discoveries from existing trait datasets as new, denser genetic marker datasets are generated for existing community association populations., (© The Author(s) 2021. Published by Oxford University Press on behalf of Genetics Society of America.)

Modern maize was domesticated from Zea mays parviglumis, a teosinte, about 9000 years ago in Mexico. Genes thought to have been selected upon during the domestication of crops are commonly known as domestication loci. The ramosa1 (ra1) gene encodes a putative transcription factor that controls branching architecture in the maize tassel and ear. Previous work demonstrated reduced nucleotide diversity in a segment of the ra1 gene in a survey of modern maize inbreds, indicating that positive selection occurred at some point in time since maize diverged from its common ancestor with the sister species Tripsacum dactyloides and prompting the hypothesis that ra1 may be a domestication gene. To investigate this hypothesis, we examined ear phenotypes resulting from minor changes in ra1 activity and sampled nucleotide diversity of ra1 across the phylogenetic spectrum between tripsacum and maize, including a broad panel of teosintes and unimproved maize landraces. Weak mutant alleles of ra1 showed subtle effects in the ear, including crooked rows of kernels due to the occasional formation of extra spikelets, correlating a plausible, selected trait with subtle variations in gene activity. Nucleotide diversity was significantly reduced for maize landraces but not for teosintes, and statistical tests implied directional selection on ra1 consistent with the hypothesis that ra1 is a domestication locus. In maize landraces, a noncoding 3'-segment contained almost no genetic diversity and 5'-flanking diversity was greatly reduced, suggesting that a regulatory element may have been a target of selection.