Identification of Allele-Specific Expression Genes Associated with Maize Heterosis

Deciphering the molecular basis of heterosis would yield genes and markers for designing improved maize-hybrid varieties. In this study, 481 BC1F3 lines derived from Zheng58 and PH4CV were genotyped with 15,386 polymorphic SNPs markers and testcrossed with two testers (Chang7-2 and PH6WC) to generate 962 testcross lines. The yield of these testcross lines and their parental lines was evaluated across multiple environments. Genetic analysis revealed that dominance is the primary contributor to heterosis. Mapping of midparent heterosis (MPH) identified two dominant QTL, six additive-by-additive interactions, eighteen additive-by-dominance interactions, and fifty-four dominance-by-dominance interactions. These interactions encompassed 104 genetic blocks, including 24 genetic blocks that explained >1% of phenotypic variances for both MPH and hybrid performance. We compared the locations of the allele-specific expression genes (ASEGs) identified from the expression data of two hybrid lines and their parental lines with those of the 24 genetic blocks and found 15 ASEGs related to yield or biomass regulation, including two known genes BT2 and ZmNF-YC4. Fisher’s exact test analysis indicated a significant enrichment of these ASEGs in the 24 blocks, affirming the reliability of the MPH-mapping results. The co-expression network of six ASEGs, including BT2 and ZmNF-YC4, contained many genes related to yield or biomass regulation. This study unravels potential candidate genes and regulatory networks associated with maize heterosis.