Changes in phosphorylation of thylakoid membrane proteins in light-harvesting complex mutants from Chlamydomonas reinhardtii

Abstract

Phosphorylation of thylakoid membrane proteins was assessed in vivo in the BF3 and BF4 mutants from Chlamydomonas reinhardtii which are deficient in light-harvesting complex (LHC). Thylakoid membranes from the BF3 mutant, which was lacking in chlorophyll b, nevertheless contained significant amounts of LHC apoproteins. The phosphorylation pattern of thylakoid membrane proteins in the mutant was similar to that in the wild type. Incubation of BF3 cells in reducing conditions induced an increase in LHC phosphorylation and a fluorescence quenching at room temperature, thereby indicating that kinase-controlled state transitions still occurred in this mutant. In contrast to the BF3 mutant, the BF4 mutant still contained chlorophyll b but lacked most of the LHC apoproteins. It contained no LHC phosphoproteins and did not undergo state transitions as shown by the absence of fluorescence quenching in reducing conditions in vivo. Surprisingly, phosphorylation of the PS II subunits D2 and 6 (CP IV apoprotein) was totally abolished in this mutant. However, the two PS II subunits of low molecular weight, L5 and L6, were still slightly phosphorylated.