Exploring the Link between Photosystem II Assembly and Translation of the Chloroplast psbA mRNA

Photosystem II (PSII) in chloroplasts and cyanobacteria contains approximately fifteen core proteins, which organize numerous pigments and prosthetic groups that mediate the light-driven water-splitting activity that drives oxygenic photosynthesis. The PSII reaction center protein D1 is subject to photodamage, whose repair requires degradation of damaged D1 and its replacement with nascent D1. Mechanisms that couple D1 synthesis with PSII assembly and repair are poorly understood. We address this question by using ribosome profiling to analyze the translation of chloroplast mRNAs in maize and Arabidopsis mutants with defects in PSII assembly. We found that OHP1, OHP2, and HCF244, which comprise a recently elucidated complex involved in PSII assembly and repair, are each required for the recruitment of ribosomes to psbA mRNA, which encodes D1. By contrast, HCF136, which acts upstream of the OHP1/OHP2/HCF244 complex during PSII assembly, does not have this effect. The fact that the OHP1/OHP2/HCF244 complex brings D1 into proximity with three proteins with dual roles in PSII assembly and psbA ribosome recruitment suggests that this complex is the hub of a translational autoregulatory mechanism that coordinates D1 synthesis with need for nascent D1 during PSII biogenesis and repair.

Lack of long-lived quantum coherence in the photosynthetic energy transfer

We have studied the FMO, LHCII and PSII reaction center complex by electronic 2D spectroscopy. At ambient temperature the electronic coherences are too short lived to play any functional role in the natural energy transfer.

Effects of water stress and rewatering on turnover and gene expression of photosystem II reaction center polypeptide D1 in Zea mays

Photosystem II oxygen evolution capacity, the steady-state level of photosystem II (PSII) reaction center polypeptide D1 and its transcript and template levels inZea mays L. (Xinyu No. 4) under water stress and rewatering were studied. The results indicated that PSII and whole-chain electron transport capacities decreased slightly under moderate water stress and appreciably under severe water stress, and could not recover to control level upon rewatering. The results of western and northern blots showed that the content of PSII reaction center polypeptide D1 changed as a similar pattern to PSII and whole-chain electron transport capacities. Dot blot analysis for DNA showed that there was no obvious response of the template level of D1 to water stress or rewatering. From the results, it was concluded that PSII was the major site affected by water stress, where the functional loss of PSII could be attributed to the reduction of PSII reaction center polypeptide D1, which may be caused by the decrease in its transcript level. Rewatering could only ameliorate slightly under moderate water stress but could not recover to control level under severe water stress.