A protein phosphatase 2A from Fagus sylvatica is regulated by GA3 and okadaic acid in seeds and related to the transition from dormancy to germination

Abstract

Several gibberellic acid (GA3)-induced cDNA fragments encoding putative serine/threonine protein phosphatase (PP) 2A catalytic subunits were obtained by means of differential reverse transcriptase-PCR approach. The full-length clone, named FsPP2A1, isolated from a beechnut cDNA library, exhibited all the features of and homology to members of the PP2A family. By transient expression of FsPP2A1 in tobacco and Arabidopsis cells as a green fluorescent fusion protein, we have obtained evidence supporting the subcellular localization of this protein in both the cytosol and the nucleus. Analysis of FsPP2A1 expression during seed stratification shows that these transcripts increase in the presence of GA3, a treatment proved to be efficient in breaking the dormancy of Fagus sylvatica seeds, but they are almost undetectable in dormant seeds or when dormancy is maintained after treatment with either abscisic acid or the gibberellin biosynthesis inhibitor paclobutrazol. The PP inhibitor okadaic acid (OKA) has a clear effect in decreasing both seed germination and FsPP2A1 expression. Furthermore, FsPP2A1 is specifically expressed in seed tissues, not being detected in other vegetative tissues examined. These results show the regulation of this PP by GA3 and OKA in these seeds. Its relationship with the processes taking place during the transition from dormancy to germination is also discussed.