Residue P132 of PsbS plays an important role in regulating the dynamics of non-photochemical quenching in Arabidopsis

Increasing the dynamics of non-photochemical quenching (NPQ) under changing light levels represents a promising strategy for improving photosynthetic light-use efficiency for greater crop yields. PsbS plays a crucial role in modulating both the capacity and dynamics of NPQ. Nevertheless, the specific mechanisms by which PsbS mediates functional state transitions and the detailed molecular interactions involved in NPQ are still not fully understood. In this study, we identified an amino acid residue, P132, in Arabidopsis thaliana PsbS (AtPsbS) whose substitution with alanine (P132A) causes rapid NPQ induction under low light and significantly reduces the rate of NPQ relaxation in the dark. Our findings suggest that the AtPsbS_P132A mutation keeps PsbS in a loose dimer state that is prone to dissociation and hence causes a reduced proportion of dimers and altered NPQ dynamics. Our study also shows that the AtPsbS_{P132A+E122Q+E226Q} mutant, which lacks protonation-sensing amino acids, may partially induce NPQ even in the absence of protonation, indicating that the structural features of PsbS may independently influence NPQ. Data from this study provide strong evidence that the structural features of PsbS affect NPQ induction and point to a significant role of the PsbS sequence in NPQ dynamics, in addition to the commonly assumed importance of PsbS levels and protonation of E122 and E226 in PsbS. In other words, the protonation sites (i.e., E122 and E226) and the amino acid residues that alter the structural characteristics of the PsbS protein both have an important effect on its NPQ function.