Isolation of the rice DL gene by positional cloning.

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The drooping leaf (dl) in rice (Oryza sativa) mutant shows homeotic conversion of carpels into stamens and drooping leaf without midrib. To elucidate the molecular function of the DL gene and to understand mechanism underlying flower development in rice, we have tried to isolate the DL gene by positional cloning. First, the dl locus was mapped within the RFIJP markers and the BAC contig covering about 250kb was constructed. Then, using a mutant probably caused by chromosomal deletion, the region involving the dl locus was confined within 50kb. Finally, the DL gene was isolated in combination with transposon tagging using TOS17. Sequence and Southern blot analyses revealed that eight dl alleles have mutations, of which severity was associated with that of their phenotypes. Therefore, we concluded that we succeeded in the isolation of the DL gene. The DL gene encodes a novel class of transcription factor, which is not found in any ABC genes so far reported. These findings suggest that the flower development in rice is regulated by the mechanisms distinct from that in Arabidopsis and Antirrhinum.