Molecular Evolution Of The Sorghum Maturity Gene Ma₁an Identification Of Quantitative Trait Loci Controlling Maturity Of Sorghum （Sorghum Bicolor （L.） Moench）

Time to maturity is a critical trait in sorghum (Sorghum bicolor) breeding, as it determines whether a variety can be grown in a particular cropping system or ecosystem. Identifying gene loci related to the maturity of sorghum and understanding the nucleotide variation and the mechanisms of molecular evolution of the maturity genes would be helpful for breeding programs. In this study, we analyzed the nucleotide diversity of Ma3and Ma1, two important maturity genes in sorghum, using252cultivated and wild sorghum materials from all over the world, and sequenced several genes around them to search for selective sweep. Meanwhile, we used an F2mapping population derived from a cross between Hiro-1and Early Hegari (both of them flower early but the F1flowers very late) trying to figure out the QTLs controlling flowering time. The main results of our research are as follows:1. We found that purifying selection was the strongest force on Ma3, as low nucleotide diversity and low-frequency amino acid variants were observed. However, a very special mutation, described as ma3R, seemed to be under positive selection, as indicated by dramatically reduced nucleotide variation not only at the loci but also in the surrounding regions among individuals carrying the mutations.2. We also detected a selective sweep around Ma1among individuals harboring either Sbprr37-1or Sbprr37-3mutation. But the level of nucleotide diversity of Ma1between cultivated and wild sorghum materials was almost the same. So we guess that diversifying selection on different alleles of Ma1balanced the positive directional selection on the recessive mutations.3. In an association study using the Ma3nucleotide variations, we detected3significant SNPs for the heading date at a high-latitude environment (Beijing) and17at a low-latitude environment (Hainan).4. QTLs affecting maturity of sorghum were detected on chromosome3,4,6and9, using genotype information identified by89polymorphic SSR markers that equally covered10chromosomes of sorghum combined with their trait information in a Hiro-1xEarly Hegari F2population consisting of188individuals. We also used the same F2population comprised of123individuals in2014summer to conform the result and detected the same QTLs except those on chromosome3.