Differential Expression of three Arabidopsis Genes Encoding the B′ Regulatory Subunit of Protein Phosphatase 2A

Abstract

Numerous plant processes ranging from signal transduction to metabolism appear to be mediated, in part, by type 2A protein serinekhreonine 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 Arabidopsis thaliana. Specifically, we used PCR to amplify a segment of Arabidopsis cDNA that encodes a conserved section of the B' polypeptide. This PCR fragment was subsequently used as a probe to screen an Arabidopsis cDNA library and cDNA clones derived from three distinct genes were identified. The AtB'a and AtB'P genes encode highly similar 57-kDa B' regulatory subunits while the third gene, AtB'y, encodes a more divergent 59-kDa B' protein. A comparison of the three Arabidopsis B' polypeptides to those of yeast and animals shows the core region of this protein to be the most conserved while the amino and carboxy termini vary both in length and sequence. Genomic Southern blots indicate that at most the Arabidopsis genome contains five genes encoding the B' regulatory subunit. The three genes identified in this study are expressed in all Arabidopsis organs, albeit at varying levels. In addition, mRNAs derived from the three genes accumulate differentially in response to heat shock. Our results indicate that the activity of plant PP2A might be regulated by a B' type regulatory subunit similar to those found in animals and yeast, and suggest possible roles for B'-containing PP2A complexes within plant cells.

Calcium Signaling: Linking Environmental Signals to Cellular Functions

“…Most of the plants show a presence of a multigene family for protein phosphatases and show differential expression in different plant parts; however, their role in calcium signaling remains to be elucidated (MacIntosh and Cohen, 1989;Jogiello et al, 1992;Arino et al, 1993;Casamayor et al, 1994;Evans et al, 1994;Li et al, 1994;Pay et al, 1994;Rundle et al, 1995;Corum et al, 1996;Guo and Roux, 1996;Hammer et al, 1997;Latorre et al, 1997).…”

Modulation of plant HMG-CoA reductase by protein phosphatase 2A

“…2 Cumulative evidence indicates that PP2A participates in the signaling of diverse stress conditions. 7 On the one hand, the transcript levels of particular PP2A subunits increase or decrease in response to biotic [36][37][38][39] or abiotic [39][40][41][42][43][44][45][46][47] challenges. On the other, PP2A activity or particular PP2A subunits participate as positive or negative transducers in the signaling of abscisic acid (ABA), [48][49][50] and ethylene, 51,52 in the response to cold 53 or drought, 45 or to ionic, osmotic and oxidative stress, 54 and in the defense against biotic challenge.…”

Protein Kinases and Phosphatases and Their Role in Cellular Signaling in Plants

“…Thus, multiple isoforms of the catalytic subunit of protein phosphatase 2A seems to exist, indicating a fair degree of complexity of this protein family (Casamayor et al, 1994). Latorre et al (1997) also observed a differential expression of three Arabidopsis genes encoding B′ regulatory subunit of PP2A. Three cDNA clones were obtained using PCR products as a probe.…”