The transition from vegetative to reproductive growth is critical in flowering plants. INDETERMINATE1 (ID1), a monocot-specific zinc finger transcription factor (TF), is thought to promote flowering by indirectly influencing ZCN8, the encoded protein of which transmits the florigen signal to downstream floral identity genes. However, the precise mechanism by which ID1 regulates floral transition in day-neutral maize remains poorly understood. Here, we characterized a floral transition-defective (ftd1) mutant that produces excess leaves and exhibits impaired reproductive development. Map-based cloning and complementation confirmed that ftd1 is an allele of id1. We demonstrated that ID1 is a nucleus-localized transcriptional activator that preferentially binds to the canonical GTC-core motif. Genome-wide binding and transcriptome analyses of ftd1 immature leaves identified potential target genes, including the flowering regulator gene MADS67 and the SPL gene SBP20. We further showed that ID1 physically interacts with MYB31 and TCP transcription factors, which synergistically enhance ID1-mediated transactivation of the MADS67 promoter. Genetic analyses indicated that ID1 acts epistatic to MADS67, and overexpression of MADS67 only partially rescued the id1 phenotype, indicating that MADS67 is necessary but insufficient for flowering. In parallel, the ID1-TCP20 complex activated SBP20, which in turn directly upregulated the florigen gene ZCN8. Collectively, our findings propose a dual-pathway model for ID1-mediated flowering regulation, in which ID1 orchestrates the floral transition through both a MADS67-dependent module (ID1+MYB31/TCP14/16/20-MADS67) and a parallel SBP20-ZCN8 module (ID1+TCP20-SBP20-ZCN8), thereby ensuring robust regulation of maize flowering time.
Zhou et al. (Tue,) studied this question.