RESUMEN
GDP-mannose-3', 5' -epimerase (GME), which converts GDP-mannose into GDP-L-galactose, is essential for the biosynthesis of L-ascorbic acid in higher plants. The molecular characterization of two GME genes from rice has been reported. Firstly,both cDNAs were isolated from the rice mature leaves using RT-PCR technique. By comparing their sequences with homologues from other plants, it was found that GME genes were highly conserved among plant species, though phylogenetic study showed that all known GMEs could be divided into two distinct groups corresponding to monocots and dicots. Secondly, the genomic organization of rice OsGME genes was investigated, and a similarity of splice patterns was revealed. Finally, the expression patterns of the two cDNAs have been studied in various tissues and under different stress conditions by semiquantitative RT-PCR assay. The results showed that the OsGME1 transcript was up-regulated in response to cold stress, and gibberellin might regulate L-ascorbic acid levels by affecting transcription of both OsGME genes.