Role of two phosphatases in state transition of Chlamydomonas (Plant Physiol.)

Plants and green algae can rapidly adapt to changing light conditions. Depending on light availability or other metabolic needs, Light Harvesting Complexes (LHC) II can be reallocated to photosystem I (PSI) from photosystem II (PSII) and vice versa. This is known as state transition and is mediated by kinases and antagonistic phosphatases via LHCII trimer phosphorylation. Cariti et al. characterized the homologs of two thylakoid phosphatases from Arabidopsis, PPH1 and PBCP, in Chlamydomonas to better understand the dynamics of state transition in green algae. The single mutants for each phosphatase had a slower pace of state transition and the double mutant remained locked in, thereby suggesting a role of PPH1 and PBCP in state transition. Under conditions favoring state transition, the LHCII trimers had high levels of phosphorylation in either pph1 or pbcp single mutant and pph1:pbcp double mutant. It was thus inferred that both PPH1 and PBCP had different but overlapping target proteins, thus playing a partially redundant role in state transition of Chlamydomonas. (Summary by Ananya Mukherjee @ana_m1490) Plant Physiol. 10.1104/pp.20.00384