Association Analysis of the nced and rab28 Genes with Phenotypic Traits Under Water Stress in Maize

As a very complex quantitative trait, drought tolerance has always been suspended with questions at the molecular level. Abscisic acid (ABA) is the main drought-induced hormone that regulates the expression of many genes related to drought tolerance. 9-cis-epoxycarotenoid dioxygenase (NCED) and ABA-responsive gene protein 28 (RAB28) are key enzymes in ABA biosynthesis and regulating drought tolerance induced by ABA under water stress, respectively. In this study, a total of 22 phenotypic traits including morphological traits, grain yield, and its components were investigated under water stress among 196 maize inbred lines majorly collected from five growing zones of China, and they were further genetically sequenced based on nced and rab28 genes and analyzed sequence polymorphism. The phenotypic analysis results showed that ten traits were highly related to variations of drought tolerance. The sequencing results showed low genetic diversity and evidence of neutral selection in both genes and high linkage disequilibrium level among pairwise polymorphic sites. Nucleotide diversity was significantly lower in the coding region than in non-coding regions. By mixed linear model, 13 and 11 polymorphisms of the nced and rab28 genes, respectively, were associating with phenotypic traits under water stress in two different environments. These results will be useful for further functional molecular breeding in improvement of drought tolerance.