Transcriptional mechanisms of brassinosteroid regulated plant growth and stress responses

Plant Steroid hormones, Brassinosteroids (BRs), play important roles in plant growth, development and responses to various stresses. BR signal through receptor BRI1 and BAK1 and a series signaling intermediates to control the activities of BES1/BZR1 family transcription factors that control the expression of thousands of genes, half of which are induced and the other half repressed by BR. While BES1 is known to activate BR-induced genes by itself or cooperating with co-activators, such as transcription factors, histone modification enzymes and transcription elongation factors, how BES1 mediates the BR-repressed gene expression is not known. In chapter Ⅱ, MYBL2, a small MYB family transcription repressor, was found to interact with BES1 to down-regulate BR-repressed gene expression. The loss-of-function mybl2 mutant enhances the phenotype of a weak allele of bri1 and suppresses the constitutive BR-response phenotype of bes1-D, suggesting that suppression of BR-repressed gene expression is required for optimal BR response. Moreover, MYBL2 is a substrate of GSK3-like kinase BIN2, a negative regulator functioning in inhibiting the activities of BES1/BZR1 through its phosphorylation in BR pathway. Unlike BIN2 phosphorylation of BES1/BZR1 leading to protein degradation, BIN2 phosphorylation stabilizes MYBL2, which demonstrated a dual role of BIN2 phosphorylation in BR pathway, similar to the function of GSK3 in WNT signaling pathway. Our results thus establish the mechanisms for BR-repressed gene expression and the integration of BR signaling and BR transcriptional network. In addition to promote the growth, BRs are known to be involved in drought response, but the mechanism of interactions between these two pathways remains to be established. In chapter Ⅲ, the NAC family transcription factor RD26 and its close homologs mediate crosstalk between drought and BR signaling pathway. RD26 is a direct target of BES1 and functions to inhibit BR-regulated growth as overexpression of RD26 leads to decreased plant growth and knockout of RD26 and its close homologs results in increased BR response. Global gene expression analysis revealed that RD26 modulates BR-regulated gene expression in a complex way. RD26 represses many BR-induced genes including BR-activated cell elongation genes and activates many BR-repressed genes, thereby inhibiting BR functions. On the other hand, BR signaling also inhibits drought responses through repressing the expression of RD26, its homologs and RD26-mediated drought-induced genes. The reciprocal inhibitory effects of BES1 and RD26 are mediated by their interactions on different promoter elements. This mechanism ensures that BR-induced plant growth is inhibited under drought condition that induced RD26 expression, while this mechanism also prevents unnecessary activation of drought response when plants undergo BR-induced growth, during which BES1 accumulates. Our results thus revealed a previously unknown mechanism coordinating plant growth and drought tolerance

RNA interference knockdown of BRASSINOSTEROID INSENSITIVE1 in maize reveals novel functions for brassinosteroid signaling in controlling plant architecture

Brassinosteroids (BRs) are plant hormones involved in various growth and developmental processes. The BR signaling system is well established in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) but poorly understood in maize (Zea mays). BRASSINOSTEROID INSENSITIVE1 (BRI1) is a BR receptor, and database searches and additional genomic sequencing identified five maize homologs including duplicate copies of BRI1 itself. RNA interference (RNAi) using the extracellular coding region of a maize zmbril complementary DNA knocked down the expression of all five homologs. Decreased response to exogenously applied brassinolide and altered BR marker gene expression demonstrate that zmbriI-RNAi transgenic lines have compromised BR signaling. zmbriI-RNAi plants showed dwarf stature due to shortened internodes, with upper internodes most strongly affected. Leaves of zmbriI-RNAi plants are dark green, upright, and twisted, with decreased auricle formation. Kinematic analysis showed that decreased cell division and cell elongation both contributed to the shortened leaves. A BRASSINOSTEROID INSENSITIVE1-ETHYL METHANESULFONATE-SUPPRESSOR1-yellow fluorescent protein (BES1-YFP) transgenic line was developed that showed BR-inducible BES1-YFP accumulation in the nucleus, which was decreased in zmbriI-RNAi. Expression of the BES1-YFP reporter was strong in the auricle region of developing leaves, suggesting that localized BR signaling is involved in promoting auricle development, consistent with the zmbriI-RNAi phenotype. The blade-sheath boundary disruption, shorter ligule, and disrupted auricle morphology of RNAi lines resemble KNOTTED1-LIKE HOMEOBOX (KNOX) mutants, consistent with a mechanistic connection between KNOX genes and BR signaling

Histone Lysine Methyltransferase SDG8 Is Involved in Brassinosteroid-Regulated Gene Expression in Arabidopsis thaliana

Citation: Wang, X., Chen, J., Xie, Z., Liu, S., Nolan, T., Ye, H., et al. (2014). Histone lysine methyltransferase SDG8 is involved in brassinosteroid- regulated gene expression in arabidopsis thaliana.The plant steroid hormones, brassinosteroids (BRs), play important roles in plant growth, development and responses to environmental stresses. BRs signal through receptors localized to the plasma membrane and other signaling components to regulate the BES1/BZR1 family of transcription factors, which modulates the expression of 4,000-5,000 genes. How BES1/BZR1 and their interacting proteins function to regulate the large number of genes are not completely understood. Here we report that histone lysine methyltransferase SDG8, implicated in Histone 3 lysine 36 di- and tri-methylation (H3K36me2 and me3), is involved in BR-regulated gene expression. BES1 interacts with SDG8, directly or indirectly through IWS1, a transcription elongation factor involved in BR-regulated gene expression. The knockout mutant sdg8 displays a reduced growth phenotype with compromised BR responses. Global gene expression studies demonstrated that SDG8 plays a major role in BR-regulated gene expression as more than half of BR-regulated genes are differentially affected in sdg8 mutant. A Chromatin Immunoprecipitation (ChIP) experiment showed that H3K36me3 is reduced in BR-regulated genes in the sdg8 mutant. Based on these results, we propose that SDG8 plays an essential role in mediating BR-regulated gene expression. Our results thus reveal a major mechanism by which histone modifications dictate hormonal regulation of gene expression

Transcriptional mechanisms of brassinosteroid regulated plant growth and stress responses

Plant Steroid hormones, Brassinosteroids (BRs), play important roles in plant growth, development and responses to various stresses. BR signal through receptor BRI1 and BAK1 and a series signaling intermediates to control the activities of BES1/BZR1 family transcription factors that control the expression of thousands of genes, half of which are induced and the other half repressed by BR. While BES1 is known to activate BR-induced genes by itself or cooperating with co-activators, such as transcription factors, histone modification enzymes and transcription elongation factors, how BES1 mediates the BR-repressed gene expression is not known. In chapter Ⅱ, MYBL2, a small MYB family transcription repressor, was found to interact with BES1 to down-regulate BR-repressed gene expression. The loss-of-function mybl2 mutant enhances the phenotype of a weak allele of bri1 and suppresses the constitutive BR-response phenotype of bes1-D, suggesting that suppression of BR-repressed gene expression is required for optimal BR response. Moreover, MYBL2 is a substrate of GSK3-like kinase BIN2, a negative regulator functioning in inhibiting the activities of BES1/BZR1 through its phosphorylation in BR pathway. Unlike BIN2 phosphorylation of BES1/BZR1 leading to protein degradation, BIN2 phosphorylation stabilizes MYBL2, which demonstrated a dual role of BIN2 phosphorylation in BR pathway, similar to the function of GSK3 in WNT signaling pathway. Our results thus establish the mechanisms for BR-repressed gene expression and the integration of BR signaling and BR transcriptional network. In addition to promote the growth, BRs are known to be involved in drought response, but the mechanism of interactions between these two pathways remains to be established. In chapter Ⅲ, the NAC family transcription factor RD26 and its close homologs mediate crosstalk between drought and BR signaling pathway. RD26 is a direct target of BES1 and functions to inhibit BR-regulated growth as overexpression of RD26 leads to decreased plant growth and knockout of RD26 and its close homologs results in increased BR response. Global gene expression analysis revealed that RD26 modulates BR-regulated gene expression in a complex way. RD26 represses many BR-induced genes including BR-activated cell elongation genes and activates many BR-repressed genes, thereby inhibiting BR functions. On the other hand, BR signaling also inhibits drought responses through repressing the expression of RD26, its homologs and RD26-mediated drought-induced genes. The reciprocal inhibitory effects of BES1 and RD26 are mediated by their interactions on different promoter elements. This mechanism ensures that BR-induced plant growth is inhibited under drought condition that induced RD26 expression, while this mechanism also prevents unnecessary activation of drought response when plants undergo BR-induced growth, during which BES1 accumulates. Our results thus revealed a previously unknown mechanism coordinating plant growth and drought tolerance.</p

Water-gas ratio characteristics and development concepts for water-producing gas reservoirs

Water production from gas wells is a key factor affecting the effectiveness of gas-reservoir development, and it poses serious challenges in terms of increasing the degree of recovery during the waterless production stage and reducing the impact of water production on gas-reservoir development in the middle and later periods. Thus, gas reservoirs must be efficiently exploited on the basis of identifying gas-water layers accurately, defining gas-water relationships, and understanding gas-water production performance. Accordingly, this study analyzes the production characteristics in gas reservoirs with different gas-water relationships, and it summarizes the rules that determine water-gas ratios. The results reveal that the water-gas ratio increases rapidly in the early stage of water production, but after a period of time, it enters a relatively stable state in which it is almost a fixed value. According to the material balance equation, the theoretically calculated water-gas ratio is fully consistent with the production rules for an entire confined gas reservoir. This shows that the reality of gas-well-water production must be faced, and that the development of water-bearing gas reservoirs must accommodate gas and water co-production. The gas-water relationship, water body scale, and reservoir heterogeneity determine the time of water breakthrough and the water-gas ratio. Therefore, we should change the traditional “water fear” concept in gas-field development, aim for an overall improvement in recovery, face up to the fact that gas wells produce water, and coordinate the development of multi-wells for entire gas reservoirs, all of which will achieve the ultimate goal of improved gas recovery

Experimental Study on the Effective Utilization of Reserves in Tight Sandstone Gas Reservoirs and Their Applications

The effective utilization of reserves in tight sandstone reservoirs is one of the major concerns in terms of the development of tight sandstone gas reservoirs. However, the characteristics of reserve utilization are not fully understood, and many uncertainties still exist in the process. For this purpose, long cores on the Su 6 block of Sulige tight sandstone gas field in China were selected, and a multipoint embedded measurement system was established to study the characteristics of effective reserve utilization. Then, the effects of the related reservoir properties and production parameters were investigated. Based on the similarity theory, the effective conversion relationship between the physical experiment and the actual field production was established. The results showed that the pressure distribution in the exploitation of tight gas reservoir is nonlinear, and water cut in the reservoir will hinder the effective utilization of reserves. The lower the reservoir permeability, the larger the negative effect of water on reservoir utilization. Lower gas production rate and higher original pressure are associated with a smoother drawdown curve, which results in larger reserve utilization. The moving boundary expands with time, and its initial propagation velocity increase and then decrease. Additionally, the water cut in the reservoir can delay the spread of moving boundary propagation. The experimental results are consistent with the actual results of the field production by the similarity criterion, which can reflect and predict the production performance in tight gas reservoirs effectively. These results can provide a better understanding of reservoir pressure distribution and effective utilization of reserves to optimize the gas recovery and development benefit in tight sandstone gas reservoirs