Molybdenum cofactor biosynthesis gene ZmCNX6 regulates vivipary and drought tolerance in maize

Pre-harvest sprouting (PHS) or vivipary is a major problem affecting cereal quality and grain quantity and is primarily linked to the dysregulation of abscisic acid (ABA) biosynthesis in plants. Therefore, elucidating the molecular mechanisms governing seed dormancy is crucial for developing strategies to improve crop productivity. In this study, we identified a novel viviparous maize mutant, viviparous-like 5 (vp-like5), which exhibits precocious germination in developing seeds. Through map-based cloning, we discovered that ZmCNX6, which encodes a small subunit of molybdopterin synthase essential for molybdenum cofactor (MoCo) biosynthesis, is the causal gene responsible for the vp-like5 phenotype. Biochemical assays have demonstrated significantly reduced activities of MoCo-dependent enzymes, including aldehyde oxidase (AO), xanthine dehydrogenase (XDH), and nitrate reductase (NR), in vp-like5. AO is essential for the ABA biosynthesis, and the observed ABA deficiency in vp-like5 likely drives the viviparous phenotype. Expression analysis showed that ZmCNX6 was stably expressed during seed development, indicating its significant role in seed development. Furthermore, overexpression of ZmCNX6 not only enhanced the activities of MoCo-dependent enzymes but also improved drought tolerance in maize. Collectively, our study revealed ZmCNX6 as a multifunctional hub coordinating MoCo metabolism, ABA-dependent dormancy regulation, and abiotic stress responses, offering a potential target for simultaneously mitigating vivipary and improving drought resistance in maize.