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 Arabidopsis thaliana and other organisms the regulatory B subunits 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-b55 alpha and PP2A-b55 beta (knockout) lines showed earlier flowering than WT, whereas a PP2A-b'gamma (knockdown) line showed late flowering. Average advancements of flowering in PP2A-b55 mutants were 3.4 days in continuous light, 6.6 days in 12 h days, and 8.2 days in 8 h days. Average delays in the PP2A-b'gamma mutant line were 7.1 days in 16 h days and 4.7 days in 8 h days. Expression of marker genes of genetically distinct flowering pathways (CO, FLC, MYB33, SPL3), and the floral integrator (FT, SOC1) were tested in WT, pp2a mutants, and two known flowering time mutants elf6 and edm2. The results are compatible with B55 acting at and/or downstream of the floral integrator, in a non-identified pathway. B'. was involved in repression of FLC, the main flowering repressor gene. For B'gamma the results are consistent with the subunit being a component in the major autonomous flowering pathway. In conclusion PP2A is both a positive and negative regulator of flowering time, depending on the type of regulatory subunit involved.