Residue P132 of PsbS Plays an Important Role in Regulating the Dynamics of Non-Chemical Quenching in Arabidopsis

Abstract

Increasing the dynamics of non-photochemical quenching (NPQ) to changing light levels represents a promising strategy to improve 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 the 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) can cause a rapid NPQ induction under low light and significantly reduces the rate of NPQ relaxation under dark. Our findings suggest that the AtPsbS_P132A mutation keeps PsbS in a loose dimer state, which is prone to disintegration and hence causes decreased proportion of dimers and altered NPQ dynamics. Besides, our study also shows that AtPsbS_{P132A+E122Q+E226Q} mutant, which lacks protonation-sensing amino acids, may partially induce NPQ production even in the absence of protonation, indicating that the structural feature of PsbS may independently influence the NPQ. Data from this study strongly support the structural features of PsbS impact NPQ formation, 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 play critical roles in affecting its NPQ function.

Keywords: PsbS; function state; non-photochemical quenching (NPQ); structural feature.