Expression of a gene encoding acetolactate synthase from rice complements two ilvH mutants in Escherichia coli

Acetolactate synthase (ALS) is a thiamine diphosphate-dependent enzyme in the biosynthetic pathway leading to isoleucine, valine and leucine in plants. ALS is the target of several classes of herbicides that are effective to protect a broad range of crops. In this study, we describe the functional analysis of a gene encoding for ALS from rice (OsALS). Sequence analysis of an EST from rice revealed that it harbors a full-length open reading frame for OsALS encoding a protein of approximately 69.4 kDa and the N-terminal of OsALS contains a feature of chloroplast transit peptide. The predicted amino acid sequence of OsALS is highly homologous to those of weed ALSs among plant ALSs. The OsALS expression showed that the gene was functionally capable of complementing the two ilvH mutant strains of Escherichia coli. These results indicate that the OsALS encodes for an enzyme in acetolactate synthase in rice.