Characterization of the sulfurtransferase family from Oryza sativa L

Sulfurtransferases (Str) comprise a group of enzymes widely distributed in archaea, eubacteria, and eukaryota which catalyze the transfer of a sulfur atom from suitable sulfur donors to nucleophilic sulfur acceptors. Neither the in vivo sulfur donors nor the acceptors of Str could be clearly identified in any of the organisms investigated so far. In Oryza sativa L. 24 Str (OsStr) encoding genes have been identified and subdivided into six groups according to their sequence homology. To half of the Oryza Str a direct homolog and to 40% at least a similar protein in Arabidopsis thaliana (L.) Heynh. could be allocated. Only the group comprising two-domain Str contains more Oryza Str than Arabidopsis Str. According to EST abundance analysis most of the OsStr mRNAs accumulate in several plant tissues. OsStr22, the homolog to the best characterized Str1 from Arabidopsis (AtStr1), shows the highest expression in middle-aged plants whereas AtStr1 shows the highest expression in senescent plants. Heterologously expressed and purified OsStr22 shows very low enzyme activity in comparison to the Arabidopsis and the Brassica napus L. Str. The data obtained so far constitute the basis to analyze differences among the Str family from monocotyledonous and dicotyledonous plants.