Molecular re-confirmation and floral characteristics of drooping leaf (DL) mutants generated by insertional mutagenesis in rice

Transposon tagging and insertional mutagenesis provide one of the most powerful tools in gene function studies. Here, we report a comparison between two novel drooping leaf (DL) mutants from transposon and T-DNA insertion lines of rice. DL is distinct from well-known ABC genes and a member of the YABBY gene family, and it is closely related to the CRABS CLAW (CRC) gene of Arabidopsis thaliana. Based on phenotypic analysis, DL regulated midrib formation by promoting cell proliferation in the central region of rice leaf and was necessary for the specification of carpel identity. We identified two DL mutants by screening the Ac/Ds and T-DNA insertional mutant pool of rice. Flanking sequence tag analysis indicated that both Ds and T-DNA segments were inserted in the promoter region at 3.4 kbs and 5.4 kb upstream, respectively, of the previously known OsYABBY domain. Interestingly, the progenies of DL lines of two different pools showed various degrees of leaf drooping and abnormal carpel formation. Flower structures revealed that there were more than two stigmas with normal stamens and pistils per panicle in the Ds-induced mutants. However, T-DNA induced mutant had extra stamens with staminoid carpels. These results indicate that the promoter region of DL plays an important function in regulating anther and carpel formation.