Zeaxanthin Binds to Light-Harvesting Complex Stress-Related Protein to Enhance Nonphotochemical Quenching in Physcomitrella patens

Abstract

ORCID IDs: 0000-0003-4818-7778 (A.A.); 0000-0002-0803-7591 (T.M.); 0000-0003-4735-8811 (R.B.).Nonphotochemical quenching (NPQ) dissipates excess energy to protect the photosynthetic apparatus from excess light. The moss Physcomitrella patens exhibits strong NPQ by both algal-type light-harvesting complex stress-related (LHCSR)-dependent and plant-type S subunit of Photosystem II (PSBS)-dependent mechanisms. In this work, we studied the dependence of NPQ reactions on zeaxanthin, which is synthesized under light stress by violaxanthin deepoxidase (VDE) from preexisting violaxanthin. We produced vde knockout (KO) plants and showed they underwent a dramatic reduction in thermal dissipation ability and enhanced photoinhibition in excess light conditions. Multiple mutants (vde lhcsr KO and vde psbs KO) showed that zeaxanthin had a major influence on LHCSR-dependent NPQ, in contrast with previous reports in Chlamydomonas reinhardtii. The PSBS-dependent component of quenching was less dependent on zeaxanthin, despite the near-complete violaxanthin to zeaxanthin exchange in LHC proteins. Consistent with this, we provide biochemical evidence that native LHCSR protein binds zeaxanthin upon excess light stress. These findings suggest that zeaxanthin played an important role in the adaptation of modern plants to the enhanced levels of oxygen and excess light intensity of land environments.

Heterologous Expression of Moss Light-harvesting Complex Stress-related 1 (LHCSR1), the Chlorophyll a-Xanthophyll Pigment-protein Complex Catalyzing Non-photochemical Quenching, in Nicotiana sp.

“…HPLC analysis on eluted slices showed that fractions enriched in PpLHCSR1 protein were characterized by a very high Chl a/b ratio with values between 8 and 24 (Fig. 6, C and D), suggesting that PpLHCSR1 could bind Chl b in a substoichiometric amount only as reported previously for Chlamydomonas reinhardtii LHCSR3 proteins (20) and native LHCSR1 from P. patens (22).…”

“…Absorption spectra of B1 and B2 of oeLHCSR1 showed a red-shifted Qy absorption peak when compared with the corresponding fractions from WT (Fig. 3, A-D); because a red-shifted spectrum is a typical characteristic of LHCSR1 protein (20,22), this suggests LHCSR1 migrates in the region of B1 with monomeric LHCs. This characteristic was more evident in the case of N. benthamiana (Fig.…”

“…Next, we tested the aggregation state of recombinant tobacco-produced PpLHCSR1 as compared with the native P. patens LHCSR1 (22). Thylakoids were solubilized with the mild detergent ␣-DM and loaded onto a sucrose gradient, which was centrifuged at 280,000 ϫ g for ϳ22 h. The separation pattern, consisting of seven green bands, was similar in WT and oeLHCSR1 N. benthamiana or N. tabacum plants.…”

“…In Physcomitrella patens, LHCSR is responsible for most of the quenching activity (21), which is strongly enhanced by zeaxanthin binding (22), making LHCSR the ideal system for structure-function studies aimed at elucidating the properties of this molecular switch that regulates photon use efficiency in unicellular algae and mosses resuming the two functions of pH detection and quenching of the chlorophyll excited states (14,20). However, the level of LHCSR is low in thylakoids, and its physicochemical properties are similar to the highly abundant LHCs, hampering purification so far.…”

Light-harvesting antenna complexes in the moss Physcomitrella patens: implications for the evolutionary transition from green algae to land plants

“…In P. patens, LHCSR is independently functional in addition to PsbS to induce qE [8,50,51]. Unlike its orthologs in C. reinhardtii [45], the qE activity of PpLHCSR is largely reliant on the accumulation of zeaxanthin [52 ]. The two PpLHCSR isoforms, LHCSR1 and LHCSR2, are more responsible for quenching under high light or low temperature, respectively [53].…”