MOLECULAR-CLONING AND CHROMOSOMAL MAPPING OF TYPE ONE SERINE THREONINE PROTEIN PHOSPHATASES IN ARABIDOPSIS-THALIANA/

Type one serine/threonine protein phosphatases (PP1s) have been implic ated in various processes of plant growth and development. In all plan t species studied, PP1s are encoded by multigene families. Previous st udies in our laboratory identified five Arabidopsis thaliana PP1 genes (TOPP1, TOPP2, TOPP3, TOPP4 and TOPP5). In the present study, we repo rt the isolation of three additional PPI genes (TOPP6, TOPP7 and TOPP8 ). Southern blot analyses indicate that these three newly isolated gen es are single-copy genes in A. thaliana genome. All the three genes ar e expressed in roots, rosettes and flowers, although their expression levels appear to be lower than those of the five previously identified TOPP genes. Six of the eight TOPP genes were mapped to different posi tions on four of five A, thaliana chromosomes. Sequence comparison rev ealed that TOPP genes belong to different subgroups of plant PPI genes , suggesting that they may encode proteins with distinct functions.