Thylakoid grana stacking revealed by multiplex genome editing of LHCII encoding genes

Land plant chloroplasts differ from algal ones for their thylakoid membranes being organized in grana: piles of vesicles paired by their stromal surface, forming domains including Photosystem (PS) II and its antenna while excluding PS I and ATPase to stroma membranes, connecting grana stacks. The molecular basis of grana stacking remain unclear. We obtained genotypes lacking the trimeric antenna complex (Lhcb1-2-3), the monomeric Lhcb4-5-6, or both. Full deletion caused loss of grana, while either monomers or trimers support 50% stacking. The expression of Lhcb5 alone restored stacking at 50%, while Lhcb2 alone produced huge grana which broke down upon light exposure. Cyclic electron transport was maintained in the lack of stacking, while excitation energy balance between photosystems and the repair efficiency of damaged Photosystem II were affected. We conclude that grana evolved for need of regulating energy balance between photosystems under terrestrial canopy involving rapid changes in photon spectral distribution.

Physiological Attributes and Transcriptomics Analysis Reveal the Response Mechanism of Helictotrichon Virescens to Low-Temperature Stress

Background: Helictotrichon Virescens is a perennial herb mainly distributed in high altitude areas of 2000 ~ 4500 m. It is widely cultivated in the Qinghai-Tibet Plateau of China, strongly resistant to cold, and an essential part of wild herbage in this region. However, the molecular mechanism of Helictotrichon virescens response to low-temperature stress is unclear, and the key regulating genes to specific biological processes are poorly known. Results: It was used physiological and transcriptome analysis to study the cold stress response mechanism in Helictotrichon Virescens. Under low-temperature treatment at 0℃, the leaves reduced chlorophyll content and light energy absorption through light antenna complex (LHCs). As the content of chlorophyll, a and b decreased, as evident were the photoprotection effects. Besides, circadian pathway-plant is crucial for the response to cold stress in Helictotrichon Virescens. Among them, DEG encoding LHY and HY5 showed strongly up-regulated expression during cold stress in Helictotrichon Virescens. Conclusions: This study provides an opportunity to fully understand the response process of Helictotrichon Virescens to low-temperature stress. It answers the pertinent questions in perennial herbaceous cold stress research, how leaves integrate light and low-temperature signals to regulate circadian rhythms in crops, and how leaf tissue reduces light absorption and enhances light protection through optical antenna complex (LHCs).

The 2.4 Å cryo-EM structure of a heptameric light-harvesting 2 complex reveals two carotenoid energy transfer pathways

We report the 2.4 Ångström resolution structure of the light-harvesting 2 (LH2) complex from Marichromatium (Mch.) purpuratum determined by cryogenic electron microscopy. The structure contains a heptameric ring that is unique among all known LH2 structures, explaining the unusual spectroscopic properties of this bacterial antenna complex. We identify two sets of distinct carotenoids in the structure and describe a network of energy transfer pathways from the carotenoids to bacteriochlorophyll a molecules. The geometry imposed by the heptameric ring controls the resonant coupling of the long-wavelength energy absorption band. Together, these details reveal key aspects of the assembly and oligomeric form of purple bacterial LH2 complexes that were previously inaccessible by any technique.

INFLUENCE OF LIGHT AND HEAVY LANTHANIDES ON THE PHYSIOLOGICAL PROCESSES OF Taraxacum hybernum

The current study was carried out to study the influence of light and heavy lanthanides on the physiological process of Crimean-Sagyz/ Krim-saghyz (dandelion - Taraxacum hybernum). Lanthanide belongs to the group of light or heavy; infiltration of dandelion (Crimean saghyz) seeds with light and heavy lanthanides solutions increased the germination energy by 26%. The differences in the influence of light (cerium) and heavy (lutetium) were manifested in the quantum efficiency change of the photosystem 2 (PS II). Treatment of leaves with high concentrations (100 µM) led to a decrease of Y (II), moreover, under the influence of light lanthanide, the decrease was greater by 21%. It is assumed that the effect of the used lanthanides on the dandelion photosynthetic apparatus is multidirectional. Cerium influenced the PS II antenna complex, and lutetium influenced the reaction centers. A 10-fold decrease in the concentration did not change the nature of cerium action, except that Y (II) was restored already on the second day after treatment. The effect of lutetium became noticeable only by the 8th day after treatment when Y (II) became higher than that of untreated plants. Thus, the results of the study suggested that in dandelion leaves, lanthanides with a concentration of 10 µM increased the quantum efficiency of PS II in contrast to cerium.

Structure of the light harvesting 2 complex reveals two carotenoid energy transfer pathways in a photosynthetic bacterium

We report the 2.4 Å resolution structure of the light harvesting 2 complex (LH2) from Marichromatium (Mch.) purpuratum determined by electron cryo-microscopy. The structure contains a heptameric ring that is unique among all known LH2 structures, explaining the unusual spectroscopic properties of this bacterial antenna complex. Two sets of distinct carotenoids are identified in the structure, and a network of energy transfer pathways from the carotenoids to bacteriochlorophyll a molecules is shown. The geometry imposed by the heptameric ring controls the resonant coupling of the long wavelength energy absorption band. Together, these details reveal key aspects of the assembly and oligomeric form of purple bacterial LH2 complexes that were previously inaccessible by any technique.One Sentence SummaryThe structure of a heptameric LH2 antenna complex reveals new energy transfer pathways and the basis for assembling LH rings.