Flower-predominant expression of a gene encoding a novel class I chitinase in rice (Oryza sativa L.)

A flower-predominant cDNA for a gene, termed OsChia1;175, was isolated from a cDNA library of rice pistils. Northern blot and RT-PCR analyses revealed that the OsChia1;175 gene is highly expressed in floral organs (pistils, stamens and lodicules at the heading stage) but not or at an extremely low level in vegetative organs. OsChia1;175 encodes a protein that consists of 340 amino acid residues, and the putative mature protein shows 52% to 63% amino acid identity to class I chitinases of rice or other plants. The phylogenetic tree shows that the OsChia1;175 protein is a new type of plant class I chitinase in rice. The expression of OsChia1;175 in vegetative organs is not induced by several chemicals, UV, and wounding. The soluble putative mature OsChia1;175 protein expressed in Escherichia coli exhibited chitinase activity in the assay with colloidal chitin as a substrate. Genomic Southern analysis revealed that the OsChia1;175 gene was organized as a low-copy gene family. The rice genomic library was screened and a genome clone corresponding to OsChia1;175 was isolated. The transcription start sites of the OsChia1;175 gene were mapped by primer extension analysis. The 1.2 kb putative promoter region of the OsChia1;175 gene was fused to the GUS (beta-glucuronidase) gene, and this chimeric gene was introduced to rice by Agrobacterium-mediated transformation. The flower-predominant gene expression was identified also in the transgenic rice plants. The high promoter activity was detected in the stigmas, styles, stamens and lodicules in transgenic plants. The possible functions of OsChia1;175 are discussed.