Physcomitrella patens mutants affected on heat dissipation clarify the evolution of photoprotection mechanisms upon land colonization

Abstract

Light is the source of energy for photosynthetic organisms; when in excess, however, it also drives the formation of reactive oxygen species and, consequently, photoinhibition. Plants and algae have evolved mechanisms to regulate light harvesting efficiency in response to variable light intensity so as to avoid oxidative damage. Nonphotochemical quenching (NPQ) consists of the rapid dissipation of excess excitation energy as heat. Although widespread among oxygenic photosynthetic organisms, NPQ shows important differences in its machinery. In land plants, such as Arabidopsis thaliana, NPQ depends on the presence of PSBS, whereas in the green alga Chlamydomonas reinhardtii it requires a different protein called LHCSR. In this work, we show that both proteins are present in the moss Physcomitrella patens. By generating KO mutants lacking PSBS and/or LHCSR, we also demonstrate that both gene products are active in NPQ. Plants lacking both proteins are more susceptible to high light stress than WT, implying that they are active in photoprotection. These results suggest that NPQ is a fundamental mechanism for survival in excess light and that upon land colonization, photosynthetic organisms evolved a unique mechanism for excess energy dissipation before losing the ancestral one found in algae.LHCSR | nonphotochemical quenching | photosystem | plants evolution | PSBS S unlight provides energy supporting the life of photosynthetic organisms but also leads to the formation of reactive oxygen species when in excess (1, 2). During early Devonian, when plants first colonized terrestrial habitats, they underwent no competition by other organisms. However, they had to adapt to harsher physicochemical conditions than in the original water ecosystem (3) because in the atmosphere concentration of oxygen, an inhibitor of photosynthesis, is higher (4) and concentration of carbon dioxide, the final acceptor of electrons extracted from water by photosystems, is lower. Moreover, the sessile form of life acquired on land prevented escape from rapid changes in light intensity by swimming deeper, a behavior typical of algae (5). The combination of these conditions makes it more likely that light is harvested in excess with respect to the maximal rate of photochemical reactions, and a fast and efficient photoprotection response is essential for survival.The fastest response to high light stress is provided by nonphotochemical quenching (NPQ), which consists of the thermal dissipation of the chlorophyll excited singlet states ( 1 Chl*) (6-8). NPQ has two major components: energy quenching (qE), which is activated within seconds on an increase in light intensity, and inhibitory quenching, which is slower and relaxes within 1-2 h in the dark (7, 9). In vascular plants, qE activation requires PSBS, a protein homologous to light harvesting antenna subunits of photosystems (Lhc) (10), which is activated by the accumulation of protons in the chloroplast lumen and the protonation of two glutamate residues (11). Activated PSBS induces a decrease...

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

“…Consistent with this, NPQ in P. patens depends on both PSBS and LHCSR (Alboresi et al, 2010;Gerotto et al, 2011) and presents an active xanthophyll cycle (Alboresi et al, 2008). The analysis of the P. patens genome (Koziol et al, 2007;Alboresi et al, 2008Alboresi et al, , 2011Rensing et al, 2008) revealed that the composition of its antenna system is more similar to that of vascular plants than to unicellular green algae due to the presence of genes encoding LHCb3 and LHCb6, which are not found in Chlamydomonas reinhardtii (Elrad and Grossman, 2004).…”

PHOTOSYSTEM II SUBUNIT R Is Required for Efficient Binding of LIGHT-HARVESTING COMPLEX STRESS-RELATED PROTEIN3 to Photosystem II-Light-Harvesting Supercomplexes in Chlamydomonas reinhardtii

“…It is tempting to speculate that the protein sequence harboring the Ser-40 phosphorylation site in conjunction with the N-terminal Thr phosphorylation sites in C. reinhardtii might be involved in protein-protein interaction with LHCSR3. In P. patens, both PSBS and LHCSR proteins are utilized to manage qE (Alboresi et al, 2010). As the PSII subunit PSBS is operating in qE in the moss in contrast to green algae, this might have altered the binding of LHCSR3 to the PSII-LHCII supercomplex and additionally adapted the functional requirement of PSBR, thereby promoting the evolution of a land plant PSBR amino acid sequence type.…”

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

“…P. patens also has its own unique lightharvesting antenna protein, Lhcb9 [7 ]. Furthermore, the light energy dissipation mechanism, so-called nonphotochemical quenching (NPQ), that is activated under excess light conditions is also operated by both green algal-and land plant-type proteins in P. patens [8]. Recent progress in elucidating the molecular mechanisms of NPQ induction in P. patens has been covered in detail elsewhere [9].…”

“…Interestingly, LHCSR is conserved in P. patens and S. fallax but appears to be lost in the liverwort M. polymorpha (v3.1) and the lycophyte Selaginella moellendorffii (v1.0, DOE-JGI). 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]. Also, unlike CrPsbS [47], PpPsbS is expressed under normal conditions and involved in the induction of qE [8]. Intriguingly, transient expression measurements of NPQ in Nicotiana benthamiana show that PpPsbS is able to induce faster and greater quenching than AtPsbS and CrPsbS [54].…”