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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Sustainable Agricultural Systems Laboratory » Research » Publications at this Location » Publication #345629
Title: Photosystem-II D1 protein mutants of Chlamydomonas reinhardtii in relation to metabolic rewiring and remodelling of H-bond network at QB site

Author
item ANTONACCI, AMINA - National Research Council - Italy
item LAMBREVA, MAYA - National Research Council - Italy
item MARGONELLI, ANDREA - National Research Council - Italy
item SOBOLEV, ANATOLY - National Research Council - Italy
item PASTORELLI, SANDRO - National Research Council - Italy
item BERTALAN, IVO - Martin Luther University
item JOHANNINGMEIER, UDO - Martin Luther University
item SOBOLEV, VLADIMIR - Weizmann Institite Of Science
item SAMISH, ILAN - Weizmann Institite Of Science
item EDELMAN, MARVIN - Weizmann Institite Of Science
item GIARDI, MARIA - National Research Council - Italy
item Mattoo, Autar
item REA, GIUSEPPINA - National Research Council - Italy

Submitted to: Nature Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Photosynthesis is pivotal for sustaining plant growth and yield of crops. In this context, the light-dependent photosynthetic reactions that occur in the chloroplasts are among the most sensitive to changes in the environment, including high light and high temperature. In order to minimize damage to the photosynthetic machinery, photosynthesizing organisms must optimize their photosynthetic activity and develop mechanisms to adapt to ever changing environments. One of the critical proteins housed in the chloroplasts is called photosystem II reaction center D1 protein (D1). Its instability affects the plant’s ability to maximize photosynthesis which is further compromised during high temperature and high light conditions. We created mutations in the D1 protein gene to test if a more vibrant protein variant could possibly be less susceptible to environmental extremes, and if so, what mechanism(s) might be involved. Here, we demonstrated that the A250R mutation to the D1 protein gene resulted in more resistance to a high light and high temperature environment while the S264K mutation resulted in relatively more susceptibility. Moreover, the A250R mutation caused changes in several metabolic pathways, suggesting remodelling of metabolism. Also revealed by this study were two important findings. First, the important role carotenoids play in stress responses and, second, D1 protein’s moonlighting function in catalysing communication between the chloroplast and the nucleus in the plant cell. These findings are important to scientists, industry and teachers.

Technical Abstract: Two mutants of the photosystem II (PSII) reaction center D1 protein, A250R and S264K, together with the control (parental intron-less, IL), Chlamydomonas reinhardtii were analyzed for changes in photosynthesis parameters, growth, and targeted metabolome under normal and dual-stress (high temperature and high photon fluence – HT/HL conditions). Both mutations impeded the reoxidation rate of the primary quinone electron acceptor QA, oxygen production capacity and photosynthetic efficiency without severely affecting maximum quantum yield of PSII. However, the effects were more pronounced in the S264K than A250R mutant. Targeted metabolomics revealed that the mutant lines have specific differences in primary and secondary metabolism, in particular amino acids, organic acids, pigments and NAD, suggesting an impact on metabolic pathways. Further, S264K and A250R mutants were found differentially impacted in the content of xanthophylls (violaxanthine+anteraxanthine), lutein and '-carotene but not zeaxanthin - the accessory pigments that promote light-harvesting and/or photoprotection. Changes in the levels of lutein, ß-carotene and zeaxanthin were in sync with their corresponding gene transcripts in response to HT/HL treatment in IL and A250R strains. The A250R and S264K mutations differentially impact QB binding and, therefore, can modify electron flow rate from PSII to PSI. D1 structure analysis indicated that substitution of D1 protein Ser264 with Lys (S264K), destroyed the H-bond between QB and His252, destabilizing the binding niche, while Ala250 substitution with Arg (A250R) led to new H-bonds in the QB pocket, stabilizing the interactions. Thus, photosynthetic performance in A250R and the parental strain were not too different, while the S264K mutant was impaired in photosynthetic performance under both normal and HT/HL conditions. These results demonstrate that the PSII reaction center D1 protein, in addition to being pivotal for the maintenance of efficient photosynthesis, is associated with remodeling of specific metabolic pathways. We propose PSII D1 protein as a regulatory site in the chloroplast for studying retrograde signalling pathways.