Size and Fluorescence Properties of Algal Photosynthetic Antenna Proteins Estimated by Microscopy

Antenna proteins play a major role in the regulation of light-harvesting in photosynthesis. However, less is known about a possible link between their sizes (oligomerization state) and fluorescence intensity (number of photons emitted). Here, we used a microscopy-based method, Fluorescence Correlation Spectroscopy (FCS), to analyze different antenna proteins at the particle level. The direct comparison indicated that Chromera Light Harvesting (CLH) antenna particles (isolated from Chromera velia) behaved as the monomeric Light Harvesting Complex II (LHCII) (from higher plants), in terms of their radius (based on the diffusion time) and fluorescence yields. FCS data thus indicated a monomeric oligomerization state of algal CLH antenna (at our experimental conditions) that was later confirmed also by biochemical experiments. Additionally, our data provide a proof of concept that the FCS method is well suited to measure proteins sizes (oligomerization state) and fluorescence intensities (photon counts) of antenna proteins per single particle (monomers and oligomers). We proved that antenna monomers (CLH and LHCIIm) are more “quenched” than the corresponding trimers. The FCS measurement thus represents a useful experimental approach that allows studying the role of antenna oligomerization in the mechanism of photoprotection.

Leaf Transcriptome Analysis of Medicago Ruthenica, Revealing Its Response and Adaptive Strategy to Drought Stress and Rehydration

Background: Recently, drought stress has brought tremendous loss on the production of agriculture and animal husbandry. In realistic production, plants are often in cyclic wet-dry environment. Therefore, the factors that affect the final yield of plants in adversity including the resistance and tolerance to drought and the ability of plants to resume from the previous damage after rehydration. So it’s necessary for us to study the response and adaptive strategies of plants to drought and rehydration. Generally, the yield of herbage with strong resistance is relatively low. However, Medicago ruthenica(L.)cv.Zhilixing has the advantages of strong resistance and high yield concurrently. This made it can be used for raising livestock, natural grassland improvement, as a good parent for breeding and a new and high quality resource of stress resistance genes. Now, there are still many problems need to be solved when compared with other important legume forages. Therefore, we analyzed the changes of Medicago ruthenica(L.)cv.Zhilixing on transcription level under drought stress and rehydration, explored its phased response strategies.Results: We obtained 191 DEGs in drought stress, and the three treatments has 43 DEGs in common. Galactose metabolism, Starch and sucrose metabolism, Arginine and proline metabolism, TCA cycle, Photosynthesis-antenna proteins, were involved in the adaptation of Medicago ruthenica to 9 days of drought stress. The regulation of Arginine and proline metabolism, Cysteine and methionine metabolism, Photosynthesis-antenna proteins, Ascorbate and aldarate metabolism were conducive to the resistance of Medicago ruthenica to severe drought stress. The regulation of Starch and sucrose metabolism, Flavonoid biosynthesis, Valine, leucine and isoleucine degradation, Circadian rhythm-plant was beneficial to the post drought recovery of Medicago ruthenica.Conclusions: We preliminarily analyzed the adaptation mechanism of the plant under different drought and rehydration conditions. Medicago ruthenica(L.)cv.Zhilixing adopts different strategies to adapt to different degrees of drought stress and rehydration. The research discovered the genes that can be used as candidate genes to improve stress resistance and drought adaptability of plants. Our transcriptome data dramatically enriches the resources of stress resistance genes. It can provide theoretical support for further adaptation mechanism research of the plant under different drought and rehydration conditions.

Generation of New Salt-Tolerant Wheat Lines and Transcriptomic Exploration of the Responsive Genes to Ethylene and Salt Stress

Background: Wheat (Triticum aestivum L.) is a staple crop in the world, but is only moderately salt tolerant. However, salt stress affects one-fifth of irrigated agricultural land in the world, it is of great importance to cultivate salt-tolerant varieties to improve the global wheat production. Results: In this study, over 90,000 wheat seeds of cultivar ‘Luyuan502’ were mutated by EMS, and 2000 salt-tolerant lines were harvested from salinized field. By analysis of ethylene sensitivity, salt related physiological factors, and preliminary crop yield, 12 salt-tolerant wheat lines with high production were selected among the crop plants. Transcriptome analysis indicated that a large number of the transcripts levels were significantly altered, mainly based on antenna proteins involved in photosynthesis, biosynthesis of secondary metabolites, cyanoamino acid metabolism, carotenoid biosynthesis, thiamine metabolism, and cutin, suberine and wax biosynthesis pathways including CABs, PERs/PODs, BGLUs, CYP707s, and ZEPs. qRT-PCR analysis revealed that the expressions of salt-related genes in the wheat lines were mostly higher than the wild type, and salt stress can significantly increase the expression levels of the ethylene-related genes in the wheat lines. Based on transcriptomic data, nine novel wheat ERFs were identified and analyzed, and it is suggested that they may play important roles in mediation of ethylene response and salt tolerance.Conclusion: Salt-tolerant wheat mutant lines with ethylene insensitivity were obtained from screen of a wheat EMS-mutagenized pool. Transcriptome data showed that the mutant plants exhibit significant alterations in the antenna proteins involved in various biological processes. Expression analysis suggests that ERFs may mediate ethylene response and salt tolerance of the wheat lines.

Structural and functional analyses of photosystem II in the marine diatom Phaeodactylum tricornutum

A descendant of the red algal lineage, diatoms are unicellular eukaryotic algae characterized by thylakoid membranes that lack the spatial differentiation of stroma and grana stacks found in green algae and higher plants. While the photophysiology of diatoms has been studied extensively, very little is known about the spatial organization of the multimeric photosynthetic protein complexes within their thylakoid membranes. Here, using cryo-electron tomography, proteomics, and biophysical analyses, we elucidate the macromolecular composition, architecture, and spatial distribution of photosystem II complexes in diatom thylakoid membranes. Structural analyses reveal 2 distinct photosystem II populations: loose clusters of complexes associated with antenna proteins and compact 2D crystalline arrays of dimeric cores. Biophysical measurements reveal only 1 photosystem II functional absorption cross section, suggesting that only the former population is photosynthetically active. The tomographic data indicate that the arrays of photosystem II cores are physically separated from those associated with antenna proteins. We hypothesize that the islands of photosystem cores are repair stations, where photodamaged proteins can be replaced. Our results strongly imply convergent evolution between the red and the green photosynthetic lineages toward spatial segregation of dynamic, functional microdomains of photosystem II supercomplexes.

Physiological and Transcriptome Analysis of a Yellow-Green Leaf Mutant in Birch (Betula platyphylla × B. Pendula)

Chlorophyll (Chl)-deficient mutants are ideal materials for the study of Chl biosynthesis, chloroplast development, and photosynthesis. Although the genes encoding key enzymes related to Chl biosynthesis have been well-characterized in herbaceous plants, rice (Oryza sativa L.), Arabidopsis (Arabidopsis thaliana), and maize (Zea mays L.), yellow-green leaf mutants have not yet been fully studied in tree species. In this work, we explored the molecular mechanism of the leaf color formation in a yellow-green leaf mutant (yl). We investigated the differentially expressed genes (DEGs) between yl and control plants (wild type birch (WT) and BpCCR1 overexpression line 11, (C11)) by transcriptome sequencing. Approximately 1163 genes (874 down-regulated and 289 up-regulated) and 930 genes (755 down-regulated and 175 up-regulated) were found to be differentially expressed in yl compared with WT and C11, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis for DEGs revealed that photosynthesis antenna proteins represent the most significant enriched pathway. The expressions of photosynthesis antenna proteins are crucial to the leaf color formation in yl. We also found that Chl accumulate, leaf anatomical structure, photosynthesis, and growth were affected in yl. Taken together, our results not only provide the difference of phenomenal, physiological, and gene expression characteristics in leaves between yl mutant and control plants, but also provide a new insight into the mutation underlying the chlorotic leaf phenotype in birch.

Stomata control is changed in a chlorophyll b-free barley mutant

The barley (Hordeum vulgare L.) chlorina f2 3613 mutant exhibits low photosynthesis and slow growth. This results from downregulation of the levels of photosynthetic antenna proteins caused by the absence of chl b, the major regulator of photosynthetic antennae in land plants. Here, we demonstrate that, when grown in the field in full sunlight, this mutant displays a changed pattern of stomatal responses compared with the parental wild-type cultivar Donaria. However, stomatal regulation of chlorina f2 3613 plants was restored when plants were placed under a shade cover for several days. The shade cover reduced incident PAR from 2000–2200 μmol m–2 s–1 to 800–880 μmol m–2 s–1 as measured at noon. Contents of ABA, the xanthophyll precursors of ABA biosynthesis and minor antenna proteins, as well as reactive oxygen species levels in stomata and the sensitivity of stomata to exogenously supplied ABA, were determined in leaves of wild-type Donaria and chlorina f2 3613 before and after shading. The results support the view that the restoration of stomatal control in barley chlorina f2 3613 is correlated with an increase in the levels of the minor antenna protein Lhcb6, which has recently been implicated in the enhancement of stomatal sensitivity to ABA in Arabidopsis thaliana (L.) Heynh.