Loss of algal Proton Gradient Regulation 5 increases reactive oxygen species scavenging and H2 evolution

Summary We have identified hpm91, a Chlamydomonas mutant lacking Proton Gradient Regulation5 （PGRS） capable of producing hydrogen （H2） for 25 days with more than 3o-fold yield increase compared to wild type. Thus, hpm91 displays a higher capacity of H2 production than a previously characterized pgr5 mutant. Physiological and biochemical characterization of hpm91 reveal that the prolonged H2 production is due to enhanced stability of PSII, which correlates with increased reactive oxygen species （ROS） scavenging capacity during sulfur depriva- tion. This anti-ROS response appears to protect the photosynthetic electron transport chain from photo- oxidative damage and thereby ensures electron supply to the hydrogenase.

A bestrophin-like protein modulates the proton motive force across the thylakoid membrane in Arabidopsis

During photosynthesis, photosynthetic electron transport generates a proton motive force （pmf） across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential （△φ） and an osmotic component （△pH）. Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein （AtBest）, which is critical for pmf partitioning. While the △pH component was slightly reduced in atbest, the △φ component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching （NPQ） upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride （Cl^-） channels. Thus, our findings reveal an important Cl^- channel required for ion transport and homeo- stasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.

Nuclear EPL-HAM complex is essential for the development of chloroplasts

Chloroplasts most likely originated from the endosymbiosis of cyanobacterial ancestors,entering the eukaryotic lineage about 1.0-1.5 billion years ago(Parfrey et al.,2011;Archibald,2015).Consequently,their biogenesis depends on genetic information from both the nuclear and chloroplast genomes.Photosynthetic housekeeping genes of core components in photosystemsⅠandⅡ(PSI and PSII)are encoded by the plastid genome。

Na_(2)CO_(3)-responsive Photosynthetic and ROS Scavenging Mechanisms in Chloroplasts of Alkaligrass Revealed by Phosphoproteomics

Alkali-salinity exerts severe osmotic,ionic,and high-p H stresses to plants.To understand the alkali-salinity responsive mechanisms underlying photosynthetic modulation and reactive oxygen species(ROS)homeostasis,physiological and diverse quantitative proteomics analyses of alkaligrass(Puccinellia tenuiflora)under Na_(2)CO_(3)stress were conducted.In addition,Western blot,real-time PCR,and transgenic techniques were applied to validate the proteomic results and test the functions of the Na_(2)CO_(3)-responsive proteins.A total of 104 and 102 Na_(2)CO_(3)-responsive proteins were identified in leaves and chloroplasts,respectively.In addition,84 Na_(2)CO_(3)-responsive phosphoproteins were identified,including 56 new phosphorylation sites in 56 phosphoproteins from chloroplasts,which are crucial for the regulation of photosynthesis,ion transport,signal transduction,and energy homeostasis.A full-length Pt FBA encoding an alkaligrass chloroplastic fructosebisphosphate aldolase(FBA)was overexpressed in wild-type cells of cyanobacterium Synechocystis sp.Strain PCC 6803,leading to enhanced Na_(2)CO_(3)tolerance.All these results indicate that thermal dissipation,state transition,cyclic electron transport,photorespiration,repair of photosystem(PS)Ⅱ,PSI activity,and ROS homeostasis were altered in response to Na_(2)CO_(3)stress,which help to improve our understanding of the Na_(2)CO_(3)-responsive mechanisms in halophytes.