A new class II rice chitinase, Rcht2, whose induction by fungal elicitor is abolished by protein phosphatase 1 and 2A inhibitor

摘要

Among the four classes of chitinase, a class II chitinase had not yet been reported for rice. This paper reports the isolation and characterization of a class II acidic chitinase, Rcht2, from rice (Oryza sativa cv. Cheongcheongbyeo). The protein consists of a single polypeptide chain of 261 amino acid residues and includes a putative signal sequence of 29 amino acids at its N-terminus. It has a calculated molecular mass of 27 642 Da and an isoelectric point of 5.56. The Rcht2 chitinase lacks the cysteine-rich and hinge domains in the N-terminal region of the protein, which is the criterion for its classification as a class II chitinase. Comparison of the genomic and the cDNA sequence revealed that the coding region of Rcht2 consists of three exonsof 301, 112 and 370 bp separated by two introns of 89 and 984 bp. In suspension-cultured rice cells, the transcript level of Rcht2 was dramatically increased by treatment with both glycol chitin and fungal elicitor (derived from the cell wall fraction of Magnaporthe grisea). The application of protein phosphatase 1 and 2A inhibitors, calyculin A and okadaic acid, effectively abolished the induction of Rcht2 in response to fungal elicitor. In contrast, the activation of Rcht2 transcript was not inhibited by both cycloheximide and protein kinase inhibitors. These results demonstrate that protein dephosphorylation events play a crucial role in the elicitor-mediated induction of Rcht2 in rice cells, while de novo protein synthesis is not required for induction. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession numbers L40338 (cDNA clone) and L40336 (genomic clone).