LEAF LATERAL SYMMETRY1, a Member of the WUSCHEL-RELATED HOMEOBOX3 Gene Family, Regulates Lateral Organ Development Differentially from Other Paralogs, NARROW LEAF2 and NARROW LEAF3 in Rice

In several eudicot species, one copy of each member of the WUSCHEL-RELATED HOMEOBOX (WOX) gene family, WOX1 and WOX3, is redundantly or differentially involved in lateral leaf outgrowth, whereas only the WOX3 gene regulating the lateral domain of leaf development has been reported in grass. In this study, we show that a WOX3 gene, LEAF LATERAL SYMMETRY1 (LSY1), regulates lateral leaf development in a different manner ftom that of other duplicated paralogs of WOX3, NARROW LEAF2 (NAL2)/NAL3, in rice. A loss-of-function mutant of LSY1 exhibited an asymmetrical defect from early leaf development, which is different from a symmetric defect in a double loss-of-function mutant of NAL2/3, whereas the expression of both genes was observed in a similar domain in the margins of leaf primordia. Unlike NAL2/3, overexpression of LSY1 produced malformed leaves whose margins were curled adaxially. Expression domains and the level of adaxial/abaxial marker genes were affected in the LSY1-overexpressing plants, indicating that LSY1 is involved in regulation of adaxial-abaxial patterning at the margins of the leaf primordia. Additive phenotypes in some leaf traits of lsy1 nal2/3 triple mutants and the unchanged level of NAL2/3 expression in the lsy1 background suggested that LSY1 regulates lateral leaf development independently of NAL2/3. Our results indicated that all of the rice WOX3 genes are involved in leaf lateral outgrowth, but the functions of LSY1 and NAL2/3 have diverged. We propose that the function of WOX3 and the regulatory mode of leaf development in rice are comparable with those of WOX1/WOX3 in eudicot species.