Enhancement of regeneration of rice (Oryza sativa L.) calli by integration of the gene involved in regeneration ability of the callus

We compared the transcription patterns of calli initiated from the cultivars Koshihikari, Sasanishiki and Konansou and from isogenic lines with the aim of identifying genes correlated with good regeneration ability of the callus in rice by mRNA differential display. Koshihikari and Sasanishiki isogenic lines exhibited the same good regeneration ability as that of Konansou, and Koshihikari and Sasanishiki exhibited poor regeneration ability compared with that of Konansou. One full-length cDNA (Os22A) whose expression was elevated in the rice calli that exhibited vigorous plant regeneration was isolated. Sequence analysis revealed that Os22A is identical to the EST clones expressed in Oryza sativa in the endosperm 10 days after pollination (accession number BI797481) and in the panicle at the ripening stage (accession number AU172698). Os22A is highly homologous to a barley gene coding for glucose dehydrogenase (accession number S72926) that is specifically expressed in developing embryos. Os22A encodes a transcript of 1391 nucleotides and is specifically expressed in calli with good regeneration ability in rice. Expression of Os22A mRNA decreased or disappeared with decrease in regeneration ability. In order to characterize the function of Os22A, we integrated Os22A into rice calli (O. sativa cu. Koshihikari). Calli initiated from Koshihikari exhibited poor regeneration ability but the transformed calli showed good regeneration ability in the regeneration medium. The regeneration ability of transformed calli clearly improved by integration of Os22A. Our results suggest that Os22A is involved in plant regeneration ability of the callus. (C) 2003 Elsevier Ireland Ltd. All rights reserved.