ABSTRACT

In wheat, the transition of the inflorescence meristem to a terminal spikelet (IM>TS) determines the spikelet number per spike (SNS), an important grain yield component. In this study, we demonstrate that the plant-specific transcription factor LEAFY (LFY) physically and genetically interacts with WHEAT ORTHOLOG OF APO1 (WAPO1) and that both genes act cooperatively to increase SNS. Loss-of-function mutations in either or both genes result in significant and similar reductions in SNS. We also show that this trait is modulated by significant genetic interactions between LFY and the SQUAMOSA MADS-box genes VRN1 and FUL2, which promote the IM>TS transition. Single-molecule fluorescence in-situ hybridization revealed a down-regulation of LFY and up-regulation of the SQUAMOSA MADS-box genes in the distal part of the developing spike during the IM>TS transition, supporting the opposite roles of these genes in the regulation of SNS in wheat. This transition coincides with the partial overlap of LFY and WAPO1 transcription domains in the most developed spikelets. Understanding the genetic network regulating SNS is a necessary first step to engineer this important agronomic trait.