leafy hull sterile1 is a homeotic mutation in a rice MADS box gene affecting rice flower development

Rice contains several MADS box genes. It has been demonstrated previously t hat one of these genes, OsMADS1 (for Oryza sativa MADS box gene1), is expre ssed preferentially in flowers and causes early flowering when ectopically expressed in tobacco plants. In this study, we demonstrated that ectopic ex pression of OsMADS1 in rice also results in early flowering. To further inv estigate the role of OsMADS1 during rice flower development, we generated t ransgenic rice plants expressing altered OsMADS1 genes that contain missens e mutations in the MADS domain. There was no visible alteration in the tran sgenic plants during the vegetative stage. However, transgenic panicles typ ically exhibited phenotypic alterations, including spikelets consisting of elongated leafy paleae and lemmas that exhibit a feature of open hull, two pairs of leafy palea-like and lemma-like lodicules, a decrease in stamen nu mber, and an increase in the number of carpels. In addition, some spikelets generated an additional floret from the same rachilla. These characteristi cs are very similar to those of leafy hull sterile1 (lhs1), The map positio n of OsMADS1 is closely linked to that of lhs1 on chromosome 3, Examination of lhs1 revealed that it contains two missense mutations in the OsMADS1 MA DS domain. A genetic complementation experiment showed that the 11.9-kb gen omic DNA fragment containing the wild-type OsMADS1 gene rescued the mutant phenotypes, In addition, ectopic expression of the OsMADS1 gene isolated fr om the lhs1 line resulted in lhs1-conferred phenotypes, These lines of evid ence demonstrate that OsMADS1 is the lhs1 gene.