ABSTRACT
The Mediator complex controls transcription of most eukaryotic genes with individual subunits required for the control of particular gene regulons in response to various perturbations. In this study, we reveal the roles of the plant Mediator subunits MED16, MED14, and MED2 in regulating transcription in response to the phytohormone abscisic acid (ABA) and we determine which cis elements are under their control. Using synthetic promoter reporters we established an effective system for testing relationships between subunits and specific cis-acting motifs in protoplasts. Our results demonstrate that MED16, MED14, and MED2 are required for the full transcriptional activation by ABA of promoters containing both the ABRE (ABA-responsive element) and DRE (drought-responsive element). Using synthetic promoter motif concatamers, we showed that ABA-responsive activation of the ABRE but not the DRE motif was dependent on these three Mediator subunits. Furthermore, the three subunits were required for the control of water loss from leaves but played no role in ABA-dependent growth inhibition, highlighting specificity in their functions. Our results identify new roles for three Mediator subunits, provide a direct demonstration of their function and highlight that our experimental approach can be utilized to identify the function of subunits of plant transcriptional regulators.
ABSTRACT
Understanding the interactive effects and relationships between biochemical elements of tea leaves and the related factors, particularly climatic, cultivar, and geographic, is key for high-quality Ceylon tea production. The objectives of this study were to (1) investigate the effects of season × cultivar × agro-ecological regions (AERs) on the four tested biochemicals in fresh tea leaves, total polyphenol content (TPC), free sugar, protein, and theanine; (2) determine the relationships between, and develop a model to estimate, the biochemicals and their related factors; and (3) project the potential concentrations and distributions of four tested biochemicals in tea leaves with respect to the current and future climate. This study primarily uses inferential statistics via the Statistical Package for the Social Sciences (SPSS), cross-validation using R software, and the inverse distance weighting (IDW) approach in ArcGIS. The results demonstrate that the season, cultivar (Ceylon tea cultivars of TRI 2025 and TRI 4053), and AER and their interactions on biochemicals have significant effects (p < 0.05). The models derived in the regression analysis demonstrate the strong relationships between the independent variables and the biochemicals, with multiple correlation coefficients (R) around 0.8 and coefficient of determination (R2) around 0.6. The low standard deviation of error of prediction (SDEP < 0.1) and the high correlation coefficient of leave-one-out cross-validation (Q2) for all four biochemicals ranged from 0.56 to 0.61, which signifies the predictive ability of the models. The future projections show a considerable increase in the thresholds of all tested biochemicals. The distribution category with 'very high' concentrations of TPC and theanine is predicted to increase in the future by averages of 10% and 14%, respectively, while reducing the classes of protein and free sugar by 14% and 12%, respectively. Overall, the changing concentrations of the thresholds of relevant biochemicals and their distribution will negatively affect the final quality of tea, and these variations indicate that climate change has started to diminish Ceylon tea quality.
Subject(s)
Camellia sinensis , Climate Change , Plant Leaves , Sri Lanka , TeaABSTRACT
The Mediator16 (MED16; formerly termed SENSITIVE TO FREEZING6 [SFR6]) subunit of the plant Mediator transcriptional coactivator complex regulates cold-responsive gene expression in Arabidopsis thaliana, acting downstream of the C-repeat binding factor (CBF) transcription factors to recruit the core Mediator complex to cold-regulated genes. Here, we use loss-of-function mutants to show that RNA polymerase II recruitment to CBF-responsive cold-regulated genes requires MED16, MED2, and MED14 subunits. Transcription of genes known to be regulated via CBFs binding to the C-repeat motif/drought-responsive element promoter motif requires all three Mediator subunits, as does cold acclimation-induced freezing tolerance. In addition, these three subunits are required for low temperature-induced expression of some other, but not all, cold-responsive genes, including genes that are not known targets of CBFs. Genes inducible by darkness also required MED16 but required a different combination of Mediator subunits for their expression than the genes induced by cold. Together, our data illustrate that plants control transcription of specific genes through the action of subsets of Mediator subunits; the specific combination defined by the nature of the stimulus but also by the identity of the gene induced.
