Cloning and functional analysis of viviparous mutant vp2 in maize

Maize vivipary, the precocious germination of seeds on the ear, significantly impacts maize yield and quality. Developing vivipary-resistant maize varieties through the discovery of novel genes is crucial for agricultural production in China. In this study, the maize mutant vp2 exhibited a clear viviparous phenotype with stable inheritance, controlled by a single recessive gene. Genome sequence analysis of the vp2 mutant revealed deletions in two coding genes (Zm00001d015355 and Zm00001d015356), with Zm00001d015356 encoding p-hydroxypyruvate dioxygenase (ZmHPPD1). The hppd1 mutant also displayed a viviparous phenotype. Furthermore, test crosses between vp2 and hppd1 heterozygous plants showed a 3:1 segregation ratio between normal and viviparous kernels, suggesting that ZmHPPD1 is the candidate gene for vp2. To further investigate the mechanism by which ZmHPPD1 regulates maize vivipary, we analyzed endogenous hormone and metabolite content in the ABA synthesis pathway. The results indicated a significant decrease in ABA levels, a substantial accumulation of octahydro lycopene, and a notable reduction in purple xanthophyll, zeaxanthin, and lutein in viviparous kernels. ZmHPPD1 disrupts ABA synthesis by affecting the conversion of octahydro lycopene to lycopene, leading to the loss of dormancy and early germination of maize kernels. These findings provide valuable genetic resources for breeding vivipary-resistant maize.