Abscisic Acid Affects Phenolic Acid Content to Increase Tolerance to UV-B Stress in Rhododendron chrysanthum Pall.

The presence of the ozone hole increases the amount of UV radiation reaching a plant's surface, and UV-B radiation is an abiotic stress capable of affecting plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum) grows in alpine regions, where strong UV-B radiation is present, and has been able to adapt to strong UV-B radiation over a long period of evolution. We investigated the response of R. chrysanthum leaves to UV-B radiation using widely targeted metabolomics and transcriptomics. Although phytohormones have been studied for many years in plant growth and development and adaptation to environmental stresses, this paper is innovative in terms of the species studied and the methods used. Using unique species and the latest research methods, this paper was able to add information to this topic for the species R. chrysanthum. We treated R. chrysanthum grown in a simulated alpine environment, with group M receiving no UV-B radiation and groups N and Q (externally applied abscisic acid treatment) receiving UV-B radiation for 2 days (8 h per day). The results of the MN group showed significant changes in phenolic acid accumulation and differential expression of genes related to phenolic acid synthesis in leaves of R. chrysanthum after UV-B radiation. We combined transcriptomics and metabolomics data to map the metabolic regulatory network of phenolic acids under UV-B stress in order to investigate the response of such secondary metabolites to stress. L-phenylalanine, L-tyrosine and phenylpyruvic acid contents in R. chrysanthum were significantly increased after UV-B radiation. Simultaneously, the levels of 3-hydroxyphenylacetic acid, 2-phenylethanol, anthranilate, 2-hydroxycinnamic acid, 3-hydroxycinnamic acid, α-hydroxycinnamic acid and 2-hydroxy-3-phenylpropanoic acid in this pathway were elevated in response to UV-B stress. In contrast, the study in the NQ group found that externally applied abscisic acid (ABA) in R. chrysanthum had greater tolerance to UV-B radiation, and phenolic acid accumulation under the influence of ABA also showed greater differences. The contents of 2-phenylethanol, 1-o-p-coumaroyl-ß-d-glucose, 2-hydroxy-3-phenylpropanoic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-o-feruloylquinic ac-id-o-glucoside were significantly elevated in R. chrysanthum after external application of ABA to protect against UV-B stress. Taken together, these studies of the three groups indicated that ABA can influence phenolic acid production to promote the response of R. chrysanthum to UV-B stress, which provided a theoretical reference for the study of its complex molecular regulatory mechanism.

Integration of transcriptomic and proteomic analyses of Rhododendron chrysanthum Pall. in response to cold stress in the Changbai Mountains.

BACKGROUND: Cold stress is one of the abiotic stresses that affect plant growth and development, as well as life and geographical distribution important. For researching how plants react to low temperature stress, Rhododendron chrysanthum Pall. (R. chrysanthum) growing in Changbai Mountains of China is an essential study subject. METHODS AND RESULTS: R. chrysanthum was cold-treated at 4 °C for 12 h (cold-stress group-CS, and controls-CK), combined with transcriptomics (RNA-seq) and proteomics (iTRAQ) techniques, to investigate the response mechanisms of R. chrysanthum response to cold stress. Cold stress resulted in the discovery of 12,261 differentially expressed genes (DEGs) and 360 differentially expressed proteins (DEPs). Correlation of proteomic and transcriptome data, proteome regulation of distinct subcellular localization, and gene/protein functional groupings are all part of the investigation. CONCLUSIONS: The combined analysis showed that 6378 DEPs matched the corresponding DEGs when the control was compared with the cold-treated samples (CK vs CS). The analysis identified 54 DEGs-DEPs associated with cold stress. cold-tolerant DEGs-DEPs were enriched with hydrolase activity, acting on glycosyl bonds, carbon-oxygen lyase activity and ferric iron binding. Seven potential DEGs-DEPs with significant involvement in the cold stress response were identified by co-expression network analysis. These findings identify the synergistic effect of DEGs-DEPs as the key to improve the cold tolerance of R. chrysanthum and provide a theoretical basis for further studies on its cold resistance subsequently.

Phosphoproteomics of cold stress-responsive mechanisms in Rhododendron chrysanthum.

BACKGROUND: As an alpine plant, Rhododendron chrysanthum (R. chrysanthum) has evolved cold resistance mechanisms and become a valuable plant resource with the responsive mechanism of cold stress. METHODS AND RESULTS: We adopt the phosphoproteomic and proteomic analysis combining with physiological measurement to illustrate the responsive mechanism of R. chrysanthum seedling under cold (4 °C) stress. After chilling for 12 h, 350 significantly changed proteins and 274 significantly changed phosphoproteins were detected. Clusters of Orthologous Groups (COG) analysis showed that significantly changed phosphoproteins and proteins indicated cold changed energy production and conversion and signal transduction. CONCLUSIONS: The results indicated photosynthesis was inhibited under cold stress, but cold induced calcium-mediated signaling, reactive oxygen species (ROS) homeostasis and other transcription regulation factors could protect plants from the destruction caused by cold stress. These data provide the insight to the cold stress response and defense mechanisms of R. chrysanthum leaves at the phosphoproteome level.

Golden 2-like Transcription Factors Regulate Photosynthesis under UV-B Stress by Regulating the Calvin Cycle.

UV-B stress can affect plant growth at different levels, and although there is a multitude of evidence confirming the effects of UV-B radiation on plant photosynthesis, there are fewer studies using physiological assays in combination with multi-omics to investigate photosynthesis in alpine plants under stressful environments. Golden 2-like (G2-like/GLK) transcription factors (TFs) are highly conserved during evolution and may be associated with abiotic stress. In this paper, we used Handy-PEA and Imaging-PAM Maxi to detect chlorophyll fluorescence in leaves of Rhododendron chrysanthum Pall. (R. chrysanthum) after UV-B stress, and we also investigated the effect of abscisic acid (ABA) on photosynthesis in plants under stress environments. We used a combination of proteomics, widely targeted metabolomics, and transcriptomics to study the changes of photosynthesis-related substances after UV-B stress. The results showed that UV-B stress was able to impair the donor side of photosystem II (PSII), inhibit electron transfer and weaken photosynthesis, and abscisic acid was able to alleviate the damage caused by UV-B stress to the photosynthetic apparatus. Significant changes in G2-like transcription factors occurred in R. chrysanthum after UV-B stress, and differentially expressed genes localized in the Calvin cycle were strongly correlated with members of the G2-like TF family. Multi-omics assays and physiological measurements together revealed that G2-like TFs can influence photosynthesis in R. chrysanthum under UV-B stress by regulating the Calvin cycle. This paper provides insights into the study of photosynthesis in plants under stress, and is conducive to the adoption of measures to improve photosynthesis in plants under stress to increase yield.

Plant hormones and phenolic acids response to UV-B stress in Rhododendron chrysanthum pall.

Our study aims to identify the mechanisms involved in regulating the response of Rhodoendron Chrysanthum Pall. (R. chrysanthum) leaves to UV-B exposure; phosphorylated proteomics and metabolomics for phenolic acids and plant hormones were integrated in this study. The results showed that UV-B stress resulted in the accumulation of salicylic acid and the decrease of auxin, jasmonic acid, abscisic acid, cytokinin and gibberellin in R. chrysanthum. The phosphorylated proteins that changed in plant hormone signal transduction pathway and phenolic acid biosynthesis pathway were screened by comprehensive metabonomics and phosphorylated proteomics. In order to construct the regulatory network of R. chrysanthum leaves under UV-B stress, the relationship between plant hormones and phenolic acid compounds was analyzed. It provides a rationale for elucidating the molecular mechanisms of radiation tolerance in plants.

Acetylated Proteomics of UV-B Stress-Responsive in Photosystem II of Rhododendron chrysanthum.

Rhododendron chrysanthum (Rhododendron chrysanthum Pall.), an alpine plant, has developed UV-B resistance mechanisms and has grown to be an important plant resource with the responsive capacity of UV-B stress. Our study uses acetylated proteomics and proteome analysis, together with physiological measurement, to show the Rhododendron chrysanthum seedling's reaction to UV-B stress. Following a 2-day, 8-h radiation therapy, 807 significantly altered proteins and 685 significantly altered acetylated proteins were discovered. Significantly altered proteins and acetylated proteins, according to COG analysis, were mostly engaged in post-translational modification, protein turnover, and chaperone under UV-B stress. It indicates that protein acetylation modification plays an important role in plant resistance to UV-B. The experimental results show that photosynthesis was inhibited under UV-B stress, but some photosynthetic proteins will undergo acetylation modification, which can alleviate the UV-B damage of plants to a certain extent. These results will serve as the basis for more research into the intricate molecular mechanisms underlying plant UV-B adaptation.

Transcriptome and proteome depth analysis indicate ABA, MAPK cascade and Ca2+ signaling co-regulate cold tolerance in Rhododendron chrysanthum Pall.

Introduction: Cold stress is a global common problem that significantly limits plant development and geographical distribution. Plants respond to low temperature stress by evolving interrelated regulatory pathways to respond and adapt to their environment in a timely manner. Rhodoendron chrysanthum Pall. (R. chrysanthum) is a perennial evergreen dwarf shrub used for adornment and medicine that thrives in the Changbai Mountains at high elevations and subfreezing conditions. Methods: In this study, a comprehensive investigation of cold tolerance (4°C, 12h) in R. chrysanthum leaves under cold using physiological combined with transcriptomic and proteomic approaches. Results: There were 12,261 differentially expressed genes (DEGs) and 360 differentially expressed proteins (DEPs) in the low temperature (LT) and normal treatment (Control). Integrated transcriptomic and proteomic analyses showed that MAPK cascade, ABA biosynthesis and signaling, plant-pathogen interaction, linoleic acid metabolism and glycerophospholipid metabolism were significantly enriched in response to cold stress of R. chrysanthum leaves. Discussion: We analyzed the involvement of ABA biosynthesis and signaling, MAPK cascade, and Ca2+ signaling, that may jointly respond to stomatal closure, chlorophyll degradation, and ROS homeostasis under low temperature stress. These results propose an integrated regulatory network of ABA, MAPK cascade and Ca2+ signaling comodulating the cold stress in R. chrysanthum, which will provide some insights to elucidate the molecular mechanisms of cold tolerance in plants.

Biochemical and proteomics analyses of antioxidant enzymes reveal the potential stress tolerance in Rhododendron chrysanthum Pall.

BACKGROUND: Rhododendron chrysanthum Pall., an endangered species with significant ornamental and medicinal value, is endemic to the Changbai Mountain of China and can also serve as a significant plant resource for investigating the stress tolerance in plants. Proteomics is an effective analytical tool that provides significant information about plant metabolism and gene expression. However, no proteomics data have been reported for R. chrysanthum previously. In alpine tundra, the abiotic stress will lead to a severe over-accumulation of reactive oxygen species (ROS). Many alpine plants overcome the severe stresses and protect themselves from the oxidative damage by increasing the ratio and activity of antioxidant enzymes. RESULTS: In our study, wild type and domesticated Rhododendron chrysanthum Pall. were used as experimental and control groups, respectively. Proteomics method combined with biochemical approach were applied for the stress tolerance investigation of R. chrysanthum at both protein and molecular level. A total of 1,395 proteins were identified, among which 137 proteins were up-regulate in the experimental group. The activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidases (APXs), and glutathione peroxidase (GPX) were significantly higher and the expression of APXs and GPX were also increased in the experimental group. Moreover, the interaction network analysis of these enzymes also reveals that the antioxidant enzymes play important roles in the stress resistance in plants. CONCLUSIONS: This is the first report of the proteome of Rhododendron chrysanthum Pall., and the data reinforce the notion that the antioxidant system plays a significant role in plant stress survival. Our results also verified that R. chrysanthum is highly resistant to abiotic stress and can serve as a significant resource for investigating stress tolerance in plants. REVIEWERS: This article was reviewed by George V. (Yura) Shpakovski and Ramanathan Sowdhamini.