Antagonistic Regulation of Flowering Time through Distinct Regulatory Subunits of Protein Phosphatase 2A

Protein phosphatase 2A (PP2A) consists of three types of subunits: a catalytic(C), a scaffolding (A), and a regulatory (B) subunit. In Arabidopsisthaliana and other organisms the regulatory Bsubunits are divided into at least three non-related groups, B55, B’ and B″.Flowering time in plants mutated in B55 or B''genes were investigated in this work. The PP2A-b55α andPP2A-b55β (knockout) lines showed earlier flowering thanWT, whereas a PP2A-b’γ (knockdown) line showed late flowering.Average advancements of flowering in PP2A-b55 mutants were 3.4days in continuous light, 6.6 days in 12 h days, and 8.2 days in 8 h days.Average delays in the PP2A-b’γ mutant line were 7.1 days in 16h days and 4.7 days in 8 h days. Expression of marker genes of geneticallydistinct flowering pathways (CO, FLC, MYB33, SPL3), and thefloral integrator (FT, SOC1) were tested in WT, pp2a mutants,and two known flowering time mutants elf6 andedm2. The results are compatible with B55 acting at and/ordownstream of the floral integrator, in a non-identified pathway. B’γ was involved in repression of FLC, the mainflowering repressor gene. For B’γ the results are consistentwith the subunit being a component in the major autonomous flowering pathway. Inconclusion PP2A is both a positive and negative regulator of flowering time,depending on the type of regulatory subunit involved.