Maize YABBY genes drooping leaf1 and drooping leaf2 regulate floret development and floral meristem determinacy

Floral morphology is shaped by factors that modulate floral meristem activity and size, and the identity, number and arrangement of the lateral organs they form. We report here that the maize CRABS CLAW co-orthologs drooping leaf1 (drl1) and drl2 are required for development of ear and tassel florets. Pistillate florets of drl1 ears are sterile with unfused carpels that fail to enclose an expanded nucellus-like structure. Staminate florets of drl1 tassels have extra stamens and fertile anthers. Natural variation and transposon alleles of drl2 enhance drl1 mutant phenotypes by reducing floral meristem (FM) determinacy. The drl paralogs are co-expressed in lateral floral primordia, but not within the FM. drl expression together with the more indeterminate mutant FMs suggest that the drl genes regulate FM activity and impose meristem determinacy non-cell-autonomously from differentiating cells in lateral floral organs. We used gene regulatory network inference, genetic interaction and expression analyses to suggest that DRL1 and ZAG1 target each other and a common set of downstream genes that function during floret development, thus defining a regulatory module that fine-tunes floret patterning and FM determinacy.