[Structure and expression analysis of the gama-glutamylcysteine synthetase gene in rice]

Gama-glutamylcysteine synthetase (GCS) is a rate-limiting enzyme in GSH biosynthesis. The GCS gene has been cloned in Arabidopsis thaliana and other plants, but has still not been reported in rice. From rice mutant population generated from T-DNA insertion, we cloned the rice GCS gene from mutant L395 by T-DNA tag cloning method, and named it OsGCS (Genbank accession No. AJ508915). Full length OsGCS cDNA clones were obtained from a rice cDNA library by the PCR method. A comparison of the genome and cDNA sequence (Genbank accession No. AJ508916) shows that OsGCS gene is composed of 15 exons and 14 introns and coding a 493-amino acid protein. The OsGCS gene is highly homologous with the AtGCS gene in the coding region but completely different in the promoter region. The putative transcription start site (TSS) confirmed by RT-PCR was located 211 bp upstream of the translation start codon "ATG". In mutant L395, a single T-DNA copy was integrated between the second intron and second exon of OsGCS gene, causing one nucleotide deletion in the second exon and two nucleotide deletions in the second intron. No significant differences were found in Cd(2+) stress tolerance, rice GCS gene expression level and GSH content between mutant L395 and Zhonghua 11. It is possible that another GCS gene on chromosome 7 might complement function of OsGCS gene on chromosome 5.