The thylakoid lumen Deg1 protease affects non-photochemical quenching via the levels of violaxanthin de-epoxidase and PsbS

Non-photochemical quenching (NPQ), the dissipation of excess light energy as heat, has been long recognized as a major protective mechanism that minimizes the potential for oxidative damage to photosystem II (PSII) reaction centers. Two major positive contributors to NPQ are the carotenoid zeaxanthin, generated from violaxanthin by the enzyme violaxanthin de-epoxidase (VDE or NPQ1), and the thylakoid protein PsbS (NPQ4). The involvement of the lumenal Deg proteases in the repair of PSII from photoinhibition prompted us to further explore their possible role in other responses of Arabidopsis thaliana to high light. Here we show that upon exposure to high light, the single deg1 and the triple deg158 mutants display different levels and kinetics of NPQ, compared to the deg58 mutant and WT that behave alike. In response to high light, the two genotypes lacking Deg1 over-accumulate NPQ1 and NPQ4. After temporal inhibition of protein translation in vivo, the level of these two proteins in deg1 is higher than in WT. Together, the results suggest that Deg1 represents a new level of regulation of the NPQ process through adjusting the quantity of NPQ1 and NPQ4 proteins, probably through their proteolysis.