Convergent Domestication of Cereal Crops by Independent Mutations at Corresponding Genetic Loci

Abstract

Independent domestication of sorghum, rice, and maize involved convergent selection for large seeds, reduced disarticulation of the mature inflorescence, and daylength-insensitive flowering. These similar phenotypes are largely determined by a small number of quantitative trait loci (QTLs) that correspond closely in the three taxa. The correspondence of these QTLs transcends 65 million years of reproductive isolation. This finding supports models of quantitative inheritance that invoke relatively few genes, obviates difficulties in map-based cloning of QTLs, and impels the comparative mapping of complex pheno-types across large evolutionary distances, such as those that separate humans from rodents and domesticated mammals.

Candidate Genes, Quantitative Trait Loci, and Functional Trait Evolution in Plants

“…Individual genes contributing to QTL effects have been identified for some developmental traits, revealing a central role for regulatory genes in complex trait variation. QTLs have been isolated using variations of the positional cloning techniques developed for isolating genes with Mendelian effects (Frary et al 2000;Fridman et al 2000;Johanson et al 2000;Yano et al 2000Yano et al , 2001El-Assal et al 2001;Takahashi et al 2001;Liu et al 2002) and/or by testing candidate genes with relevant function that map to QTL regions (Doebley et al 1995;Wang et al 1999;Thornsberry et al 2001). Methods for testing and verification of the isolated genes may include transformation with transgenic constructs, testing for population-level association of gene polymorphisms with phenotype differences , or quantitative complementation testing (Doebley et al 1995;Mackay 2001).…”

“…The power to detect specific epistatic interactions is especially limited by multiple testing considerations in QTL experiments because the number of possible two-way interaction terms increases approximately in proportion to the square of the number of main effects. Doebley et al (1995) found that the effects of QTLs for plant architecture differences between maize and teosinte varied depending on the genetic background in which they were evaluated. More recently, Lauter and Doebley (2002) also found genetic variation for some of the same plant architecture QTLs within teosinte when hybrids between two teosinte subspecies were testcrossed to maize.…”

“…The maize tb1 locus, originally identified as a maize plant architecture mutant, was found to be responsible for important plant architecture differences between maize and teosinte (Doebley et al 1995). However, tb1 variation shows no association with phenotypic differences within maize , and analyses of tb1 sequences within the Andropogoneae tribe of grasses show no evidence of natural selection (Lukens and Doebley 2001).…”

“…The involvement of CONSTANS-like genes in flowering time variation in both rice and Brassica indicates that at least some gene families may play key roles in overall plant diversification. QTLs for quantitative traits in several cereal grains are located in corresponding chromosomal regions, implying that the same genes may be involved (Paterson et al 1995). However, selection for staygreen traits in different cereal grasses appears to involve different genetic mechanisms (Thomas and Howarth 2000).…”

Pod Shattering: A Homologous Series of Variation Underlying Domestication and an Avenue for Crop Improvement

“…Much of this evidence suggests that pathways and loci controlling shattering are deeply conserved across taxa, and that homologous mechanisms and loci underlie indehiscence [19,20]. As a consequence, these shared domestication-related loci became common targets of breeding programs.…”