<i>LATERAL FLORET 1</i> induced the three-florets spikelet in rice.

Abstract

The spikelet is a unique inflorescence structure in grass. The molecular mechanisms behind the development and evolution of the spikelet are far from clear. In this study, a dominant rice mutant, <i>lateral florets 1</i> (<i>lf1</i>), was characterized. In the <i>lf1</i> spikelet, lateral floral meristems were promoted unexpectedly and could generally blossom into relatively normal florets. <i>LF1</i> encoded a class III homeodomain-leucine zipper (HD-ZIP III) protein, and the site of mutation in <i>lf1</i> was located in a putative <i>miRNA165</i>/<i>166</i> target sequence. Ectopic expression of both <i>LF1</i> and the meristem maintenance gene <i>OSH1</i> was detected in the axil of the sterile lemma primordia of the <i>lf1</i> spikelet. Furthermore, the promoter of <i>OSH1</i> could be bound directly by LF1 protein. Collectively, these results indicate that the mutation of <i>LF1</i> induces ectopic expression of <i>OSH1</i>, which results in the initiation of lateral meristems to generate lateral florets in the axil of the sterile lemma. This study thus offers strong evidence in support of the "three-florets spikelet" hypothesis in rice.