Zea mays (maize) flowering time is genetically determined and a critical yield determinant. Yet mechanistic understanding of maize flowering remains poor. Indeterminate1 (Id1), a zinc-finger transcription factor (TF), is a monocot-conserved master regulator of maize flowering. Epistasis between Id1 and the ZeaCentroradialis-Delayed Flowering1 (Zcn-Dlf1) inductive pathway partly explains ID1 floral control; however, the strong mutant id1- floral delay is not explained by this pathway alone. To better characterize Id1 actions, we performed single-cell assay for transposase-accessible chromatin and single nucleus RNA sequencing (scATAC-seq and snRNA-seq) comparing Id1+ and id1- developing leaves. These analyses reveal id1- chromatin remodeling via TEOSINTE BRANCHED1 CYCLOIDEA PROLIFERATING CELL FACTOR (TCP) and APETALA2/ETHYLENE RESPONSEFACTOR (AP2/ERF) transcription factors and provide candidate direct targets that include AP2/ERF genes. These candidate direct targets include the family of {beta}-glucosidase genes that lose expression in id1-. Unexpectedly, CRISPR/Cas9 {beta}-glucosidase edits produced plants that phenocopied terminal ear1- (te1-) mutants. This phenocopy prompted an investigation into the genetic relationship between id1-, te1- and flowering. Surprisingly, id1- te1- plants exhibited a synergistic floral delay, producing ~90 leaves before inflorescence production. Beyond highlighting hitherto unappreciated Te1 autonomous flowering roles, this genetic synergy raises the hypothesis that meristem leaf primordia cessation underpins maize flowering.
Minow, M. A. A., Ali, Z., Sangra, A., Behrendt, N. J., Lukens, L., Colasanti, J., Schmitz, R. J.
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