Phytohormones are endogenously produced organic substances indispensable for regulating plant growth and yield and also play major role in inducing tolerance to plants against various biotic and abiotic stresses. The convergence points among hormone signal transduction cascades are considered as cross-talk which are crucial for plant development as well as for plant responses to biotic and abiotic stresses. Hormones interact by activating either a second messenger or through a phosphorylation cascade. These transduction cascades lead to the regulation of gene expression that directly affects the biosynthesis or action of different hormones and developmental processes in coordination with multiple stimuli. Hormone synthesis, signal transduction, perception and cross-talk create a complex network. Interaction of plant growth promoting rhizobacteria (PGPR) which form intimate association with the roots of higher plants also modulate the level of endogenous phytohormones and demonstrate a new paradigm for hormonal interaction. The ratio of hormones changes with ontogeny of plant and the specific ratio of growth promoting and growth inhibiting hormones determine the response of plants. Furthermore, the sensitivity of plant tissue to each hormone changes with the exposure to stresses. This review is a compilation of the interactions between phytohormones and plant development. The cross talk between different hormones under abiotic and biotic stresses will be enumerated. Hormone and stress-responsive cis elements and the trans-regulation capabilities of miRNAs for the coordination of multiple hormonal responses will be discussed. Finally the role of PGPR will be evaluated under various environmental stresses with particular emphasis on phytohormone production and its interaction with host plant physiology. PGPR provides cross protective properties through improvement in defense mechanism controlling pathogen resistance through induced systemic resistance (ISR) and alleviating abiotic stress through influencing the phytohormones metabolism. PGPR isolates from stressed soil/stressed host plants impart tolerance to plants against abiotic and biotic stresses by modulating the production of phytohormones and alteration in their sensitivity to respond. Bacteria communicate with each other through quorum sensing molecules which also regulate gene expression and phytohormone production. The intricate relationship between other microbes/fungi and their residual effects on plant rhizosphere phytohormones need further investigation for better understanding of bacterial coordination with plants.

Crosstalk amongst phytohormones from planta and PGPR under biotic and abiotic stresses

Tea is one of the most consumed beverages in the world. Green tea, black tea, and oolong tea are made from the same plant Camellia sinensis (L.) O. Kuntze. Among them, green tea has been the most extensively studied for beneficial effects on diseases including cancer, obesity, diabetes, and inflammatory and neurodegenerative diseases. Several human observational and intervention studies have found beneficial effects of tea consumption on neurodegenerative impairment, such as cognitive dysfunction and memory loss. These studies supported the basis of tea’s preventive effects of Parkinson’s disease, but few studies have revealed such effects on Alzheimer’s disease. In contrast, several human studies have not reported these favorable effects with regard to tea. This discrepancy may be due to incomplete adjustment of confounding factors, including the method of quantifying consumption, beverage temperature, cigarette smoking, alcohol consumption, and differences in genetic and environmental factors, such as race, sex, age, and lifestyle. Thus, more rigorous human studies are required to understand the neuroprotective effect of tea. A number of laboratory experiments demonstrated the benefits of green tea and green tea catechins (GTCs), such as epigallocatechin gallate (EGCG), and proposed action mechanisms. The targets of GTCs include the abnormal accumulation of fibrous proteins, such as Aβ and α-synuclein, inflammation, elevated expression of pro-apoptotic proteins, and oxidative stress, which are associated with neuronal cell dysfunction and death in the cerebral cortex. Computational molecular docking analysis revealed how EGCG can prevent the accumulation of fibrous proteins. These findings suggest that GTCs have the potential to be used in the prevention and treatment of neurodegenerative diseases and could be useful for the development of new drugs.

https://www.mdpi.com/1420-3049/23/6/1297/pdf

Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases.

The unprecedented early spring frost that appears as a cold stress adversely affects growth and productivity in tea (Camellia sinensis L.); therefore, it is indispensable to develop approaches to improve the cold tolerance of tea. Here, we investigated the effect of pretreatment with exogenous melatonin on the net photosynthetic rate, the maximum photochemical efficiency of PSII, chlorophyll content, lipid peroxidation, reactive oxygen species (ROS) accumulation, antioxidant potential, and redox homeostasis in leaves of tea plants following cold stress. Our results revealed that cold treatment induced oxidative stress by increasing ROS accumulation, which in turn affected the photosynthetic process in tea leaves. However, treatment with melatonin mitigated cold-induced reductions in photosynthetic capacity by reducing oxidative stress through enhanced antioxidant potential and redox homeostasis. This study provides strong evidence that melatonin could alleviate cold-induced adverse effects in tea plants.

https://www.mdpi.com/1420-3049/23/1/165/pdf

Exogenous Melatonin Alleviates Cold Stress by Promoting Antioxidant Defense and Redox Homeostasis in Camellia sinensis L.

Advances in the plant protein extraction: Mechanism and recommendations

Plants produce and emit terpenes, including sesquiterpenes, during growth and development, which serve different functions in plants. The sesquiterpene nerolidol has health-promoting properties and adds a floral scent to plants. However, the glycosylation mechanism of nerolidol and its biological roles in plants remained unknown. Sesquiterpene UDP-glucosyltransferases were selected by using metabolites-genes correlation analysis, and its roles in response to cold stress were studied. We discovered the first plant UGT (UGT91Q2) in tea plant, whose expression is strongly induced by cold stress and which specifically catalyzes the glucosylation of nerolidol. The accumulation of nerolidol glucoside was consistent with the expression level of UGT91Q2 in response to cold stress, as well as in different tea cultivars. The reactive oxygen species (ROS) scavenging capacity of nerolidol glucoside was significantly higher than that of free nerolidol. Down-regulation of UGT91Q2 resulted in reduced accumulation of nerolidol glucoside, ROS scavenging capacity and tea plant cold tolerance. Tea plants absorbed airborne nerolidol and converted it to its glucoside, subsequently enhancing tea plant cold stress tolerance. Nerolidol plays a role in response to cold stress as well as in triggering plant-plant communication in response to cold stress. Our findings reveal previously unidentified roles of volatiles in response to abiotic stress in plants.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.16364

Sesquiterpene glucosylation mediated by glucosyltransferase UGT91Q2 is involved in the modulation of cold stress tolerance in tea plants.

C-repeat binding factors (CBFs) are involved in multiple pathways of plant growth, development and stress responses. In this study, CsCBF3, a gene encoding a polypeptide of 274 amino acids and containing the structural feature of AP2 domain in CBF protein family, was characterized from tea plant [Camellia sinensis (L.) O. Kuntze]. CsCBF3 was located in cell nucleus and cytoplasm by subcellular localization analysis. Expression analysis revealed that CsCBF3 was induced by low temperature stress, abscisic acid and drought treatment in tea leaves. CsCBF3 overexpressed Arabidopsis displayed higher tolerance to cold stress and improved photosynthesis ability with less damage under cold condition compared to wild type plants. Furthermore, it was observed that the CsCBF3 gene regulates the expressions of downstream genes of cold responsive pathway, such as AtCOR15a and AtCOR78. These results indicate that CsCBF3 plays an important role in responding to cold stress and provide potential applications in molecular breeding to enhance cold tolerance in tea plant.

Functional analysis of CsCBF3 transcription factor in tea plant ( Camellia sinensis ) under cold stress

Background 
Alzheimer’s disease is a common neurodegenerative disorder in elderly. This study was aimed to systematically evaluate the association between tea intake and the risk of cognitive disorders by meta-analysis.


Methods and Findings 
PubMed, Embase and Wanfang databases were systematically searched and a total of 26 observational studies were included in this study. Odds ratios (ORs) and the corresponding 95% confidence intervals (CIs) were calculated and pooled by using fixed or random effects models according to the degree of heterogeneity.


Results 
The overall pooled analysis indicated that tea intake could significantly reduce the risk of cognitive disorders (OR = 0.65, 95%CI = 0.58–0.73). Subgroup analyses were conducted based on study design, population, frequency of tea drinking and type of cognitive disorders. The results showed that tea drinking was significantly associated with the reduced incidence of cognitive disorders in all of subgroups based on study design and frequency of tea drinking. In particular, tea drinking was inversely associated with the risk of cognitive impairment (CoI), mild cognitive impairment (MCI), cognitive decline and ungrouped cognitive disorders. Moreover, for population subgroups, the significant association was only found in Chinese people.


Conclusion 
Our study suggests that daily tea drinking is associated with decreased risk of CoI, MCI and cognitive decline in the elderly. However, the association between tea intake and Alzheimer’s disease remains elusive.

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0165861&type=printable

Meta-Analysis of the Association between Tea Intake and the Risk of Cognitive Disorders

Optimization of Protein Extraction and Decoloration Conditions for Tea Residues

Calmodulin-like (CML) proteins are a class of important Ca2+ sensors in plants, which play vital roles in regulating plant growth and development and response to abiotic stress. Tea plant (Camellia sinensis L.) is the most popular non-alcoholic economic beverage crop around the world. However, the potential functions of CMLs in either tea plants growth or in the response to environmental stresses are still unclear. In the present study, five CsCML genes (CsCML16, CsCML18-1, CsCML18-2, CsCML38, and CsCML42) were isolated from tea plant, and functionally characterized. The CsCML genes showed diverse expression patterns in leaves, roots, old stems, immature stems and flowers of tea plants. To investigate the expression changes of the genes under various abiotic stresses and ABA treatment, time-course experiments were also performed, the results indicated that the expression levels of CsCML16, 18-2 and 42 were significantly induced under low temperature and salt condition, while CsCML38 was induced distinctly under drought stress and ABA treatment. Overall, CsCML genes showed diverse function in tea plant under various stimuli. These results will increase our knowledge of the significance of CsCML genes in tea plant in response to abiotic stresses and hormone treatments.

Qiaoyun Cui

Papers

Functional analysis of CsCBF3 transcription factor in tea plant ( Camellia sinensis ) under cold stress

Meta-Analysis of the Association between Tea Intake and the Risk of Cognitive Disorders

Optimization of Protein Extraction and Decoloration Conditions for Tea Residues

Isolation and expression analysis of CsCML genes in response to abiotic stresses in the tea plant (Camellia sinensis)

Association between tea consumption and osteoporosis: A meta-analysis.