Regulation, expression and function of a new basic chitinase gene in rice (Oryza sativa L.).

A new basic chitinase gene, designated RC24, was isolated from a rice genomic library. The predicted RC24 protein contains 322 amino acid residues and exhibits 68% to 95% amino acid identity with known class I rice chitinases. RC24 protein expressed in Escherichia coli exhibited chitinase activity and strongly inhibited bacterial growth. Two transcription start sites of the RC24 gene were mapped by primer extension analysis of both rice native RNA and in vitro transcribed RNA using a RC24 promoter/GUS (beta-glucuronidase) gene fusion as a template. The 5'-flanking region of RC24 contained several putative stress-responsive cis-acting elements. A basal level of RC24 transcripts was detected in rice root and stem tissues, but not in leaf tissues. RC24 transcripts rapidly accumulated within 1 h after fungal elicitor treatment of suspension-cultured cells, and the levels continued to increase for at least 9 h. RC24 transcript accumulation was also observed in intact leaf tissues upon wounding, Transgenic rice plants containing the RC24/GUS gene fusion further confirmed that the RC24 gene showed a tissue-specific expression pattern and that transcription of the RC24 propmoter was sensitively and rapidly activated by wounding.