Unlocking tropical adaptation: novel flowering time genes implicate JA and ROS signaling in maize

Tropical maize germplasm offers a valuable resource of genetic diversity for temperate maize breeding programs but its utilization is often constrained by poor flowering adaptation under long-day photoperiods, which act as a major adaptive barrier in temperate environments. To dissect the genetic basis of this adaptive barrier, a multi-parent population (MPP) was developed using an elite temperate inbred (Ye107) and three tropical inbred lines exhibiting strong flowering delays under long-day photoperiods. Using genotyping-by-sequencing (GBS), a total of 579,346 high-quality SNPs were identified, and flowering-time related traits were evaluated across multiple environments. By integrating a joint-mapping strategy of genome-wide association study (GWAS) and linkage analysis, two high-confidence candidate genes were identified on chromosome 3: Zm00001d042884, encoding an acyl-CoA oxidase that likely regulates days to tasseling by affecting jasmonic acid (JA) biosynthesis and Zm00001d042961, encoding a respiratory burst oxidase homolog (RBOHH) that potentially modulates reactive oxygen species (ROS) signalling during reproductive development. We suggest that these genes operate within a bipartite regulatory framework whereby Zm00001d042884 may act as an upstream module for floral initiation and Zm00001d042961 as a downstream module for reproductive assurance, controlling pollen viability through ROS (reactive oxygen species) signaling after floral transition. The information presented here reveals previously unrecognized functional potential for JA and ROS signaling pathways regulating maize flowering adaptation, extending the present understanding of flowering regulation, traditionally based on signal perception; signal transduction, to inclusively involve a second layer of physiological regulation for reproductive assurance. Furthermore, the positive early-flowering haplotypes identified provide significant genetic targets to overcome the poor flowering adaptation of tropical germplasm under long day conditions through molecular design breeding approaches, thus accelerating the utilization and exploitation of elite trait resources from tropical germplasm in temperate maize improvement program.