DIFFERENTIAL EXPRESSION OF 3 ARABIDOPSIS GENES ENCODING THE B' REGULATORY SUBUNIT OF PROTEIN PHOSPHATASE 2A

Numerous plant processes ranging from signal transduction to metabolis m appear to be mediated, in part, by type 2A protein serine/threonine phosphatases (PP2A). In an effort to identify factors that control the activity of this enzyme in plants, we have isolated and characterized DNA sequences encoding the B' regulatory subunit of PP2A from Arabido psis thaliana. Specifically, we used PCR to amplify a segment of Arabi dopsis cDNA that encodes a conserved section of the B' polypeptide. Th is PCR fragment was subsequently used as a probe to screen an Arabidop sis cDNA library and cDNA clones derived from three distinct genes wer e identified. The AtB'alpha and AtB'beta genes encode highly similar 5 7-kDa B' regulatory subunits while the third gene, AtB'gamma, encodes a more divergent 59-kDa B' protein. A comparison of the three Arabidop sis B' polypeptides to those of yeast and animals shows the core regio n of this protein to be the most conserved while the amino and carboxy termini vary both in length and sequence. Genomic Southern blots indi cate that at most the Arabidopsis genome contains five genes encoding the B' regulatory subunit. The three genes identified in this study ar e expressed in all Arabidopsis organs, albeit at varying levels. In ad dition, mRNAs derived from the three genes accumulate differentially i n response to heat shock. Our results indicate that the activity of pl ant PP2A might be regulated by a B' type regulatory subunit similar to those found in animals and yeast, and suggest possible roles for B'-c ontaining PP2A complexes within plant cells.