Dissecting genome-wide association signals for loss-of-function phenotypes in sorghum flavonoid pigmentation traits.
Genome-wide association studies are a powerful method to dissect the genetic basis of traits, although in practice the effects of complex genetic architecture and population structure remain poorly understood. To compare mapping strategies we dissected the genetic control of flavonoid pigmentation traits in the cereal grass sorghum by using high-resolution genotyping-by-sequencing single-nucleotide polymorphism markers. Studying the grain tannin trait, we find that general linear models (GLMs) are not able to precisely map tan1-a, a known loss-of-function allele of the Tannin1 gene, with either a small panel (n = 142) or large association panel (n = 336), and that indirect associations limit the mapping of the Tannin1 locus to Mb-resolution. A GLM that accounts for population structure (Q) or standard mixed linear model that accounts for kinship (K) can identify tan1-a, whereas a compressed mixed linear model performs worse than the naive GLM. Interestingly, a simple loss-of-function genome scan, for genotype-phenotype covariation only in the putative loss-of-function allele, is able to precisely identify the Tannin1 gene without considering relatedness. We also find that the tan1-a allele can be mapped with gene resolution in a biparental recombinant inbred line family (n = 263) using genotyping-by-sequencing markers but lower precision in the mapping of vegetative pigmentation traits suggest that consistent gene-level resolution will likely require larger families or multiple recombinant inbred lines. These findings highlight that complex association signals can emerge from even the simplest traits given epistasis and structured alleles, but that gene-resolution mapping of these traits is possible with high marker density and appropriate models.
Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208.
Geoffrey P
GP
Morris
Davina H
DH
Rhodes
Zachary
Z
Brenton
Punna
P
Ramu
Vinayan Madhumal
VM
Thayil
Santosh
S
Deshpande
C Thomas
CT
Hash
Charlotte
C
Acharya
Sharon E
SE
Mitchell
Edward S
ES
Buckler
Jianming
J
Yu
Stephen
S
Kresovich
D000483:Alleles; D002874:Chromosome Mapping; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism*; D018745:Genome, Plant; D055106:Genome-Wide Association Study; D005838:Genotype; D008957:Models, Genetic; D010641:Phenotype; D010860:Pigments, Biological / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics; D020641:Polymorphism, Single Nucleotide; D045868:Sorghum / Q000235:genetics*
D005419:Flavonoids; D010860:Pigments, Biological; D010940:Plant Proteins
genome scan; grain pigmentation; null alleles; quantitative trait loci; structured populations