A putative rice l - cysteine desulfhydrase encodes a true l -cysteine synthase that regulates plant cadmium tolerance

Recent years have witnessed tremendous progress in understanding the biological relevance of hydrogen sulfide (H 2 S) as the third gasotransmitter for multiple signaling events in plants. l -Cys desulfhydrase (LCD) catalyzes the formation of H 2 S by using l -Cys as a substrate. In previous studies, we detected LCD activity in rice, but the corresponding genetic information and its biological function in the alleviation of plant Cd toxicity are still unknown. In this study, a putative LCD gene ( OsLCD2 ) with high homology to Arabidopsis LCD has been cloned in rice. Surprisingly, the biochemical characterization of the recombinant OsLCD2 protein suggests that this protein predominantly possesses cysteine synthesis activity rather than the degradation of cysteine to produce H 2 S, and thus, the gene has been renamed OsCS1 . OsCS1 localizes inside the nucleus in rice protoplasts. Molecular evidence shows that OsCS1 mRNA is ubiquitously expressed in rice, and up-regulated by cadmium. It has been further observed that over-expression of OsCS1 in Arabidopsis results in the enhanced glutathione biosynthesis, which allows plants to tolerate cadmium stress. Overall, the above findings provide evidence that OsCS1 is a potentially important enzyme responsible for the synthesis of cysteine, which could provide a new information about the metabolism of H 2 S in plants.