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SUMMARY: Suberin is a complex hydrophobic polymer of aliphatic and phenolic compounds which controls the movement of gases, water, and solutes and protects plants from environmental stresses and pathogenic infection. The synthesis and regulatory pathways of suberin remain unknown in Brachypodium distachyon. Here we describe the identification of a B. distachyon gene, BdFAR4, encoding a fatty acyl‐coenzyme A reductase (FAR) by a reverse genetic approach, and investigate the molecular relevance of BdFAR4 in the root suberin synthesis of B. distachyon. BdFAR4 is specifically expressed throughout root development. Heterologous expression of BdFAR4 in yeast (Saccharomyces cerevisiae) afforded the production of C20:0 and C22:0 fatty alcohols. The loss‐of‐function knockout of BdFAR4 by CRISPR/Cas9‐mediated gene editing significantly reduced the content of C20:0 and C22:0 fatty alcohols associated with root suberin. In contrast, overexpression of BdFAR4 in B. distachyon and tomato (Solanum lycopersicum) resulted in the accumulation of root suberin‐associated C20:0 and C22:0 fatty alcohols, suggesting that BdFAR4 preferentially accepts C20:0 and C22:0 fatty acyl‐CoAs as substrates. The BdFAR4 protein was localized to the endoplasmic reticulum in Arabidopsis thaliana protoplasts and Nicotiana benthamiana leaf epidermal cells. BdFAR4 transcript levels can be increased by abiotic stresses and abscisic acid treatment. Furthermore, yeast one‐hybrid, dual‐luciferase activity, and electrophoretic mobility shift assays indicated that the R2R3‐MYB transcription factor BdMYB41 directly binds to the promoter of BdFAR4. Taken together, these results imply that BdFAR4 is essential for the production of root suberin‐associated fatty alcohols, especially under stress conditions, and that its activity is transcriptionally regulated by the BdMYB41 transcription factor. [ABSTRACT FROM AUTHOR]

To protect above‐ground plant organs from excessive water loss, their surfaces are coated by waxes. The genes involved in wax formation have been investigated in detail in Arabidopsis but scarcely in crop species. Here, we aimed to isolate and characterize a CER1 enzyme responsible for formation of the very long‐chain alkanes present in high concentrations especially during late stages of wheat development. On the basis of comparative wax and transcriptome analyses of various wheat organs, we selected TaCER1‐1A as a primary candidate and demonstrated that it was located to the endoplasmic reticulum, the subcellular compartment for wax biosynthesis. A wheat nullisomic‐tetrasomic substitution line lacking TaCER1‐1A had significantly reduced amounts of C33 alkane, whereas rice plants overexpressing TaCER1‐1A showed substantial increases of C25–C33 alkanes relative to wild type control. Similarly, heterologous expression of TaCER1‐1A in Arabidopsis wild type and the cer1 mutant resulted in increased levels of unbranched alkanes, iso‐branched alkanes and alkenes. Finally, the expression of TaCER1‐1A was found activated by abiotic stresses and abscisic acid treatment, resulting in increased production of alkanes in wheat. Taken together, our results demonstrate that TaCER1‐1A plays an important role in wheat wax alkane biosynthesis and involved in responding to drought and other environmental stresses. In this paper, the function of TaCER1‐1A involved in wheat alkane biosynthesis was tested using gain‐of‐function (transgenic plants) and loss‐of‐function plants (gene deletion wheat line), and the role of alkanes in drought resistance was assessed. [ABSTRACT FROM AUTHOR]

Summary: In plants, the calmodulin‐binding transcription activators (CAMTAs) are required for transcriptional regulation of abiotic and biotic stress responses. Among them, CAMTA3 in Arabidopsis has been intensively studied and shown to function redundantly with CAMTA1 and CAMTA2 to negatively regulate plant immunity. The camta1/2/3 triple mutant accordingly exhibits severe dwarfism due to autoimmunity. Here, through a suppressor screen using camta1/2/3 triple mutant, we found that a mutation in Cyclin‐Dependent Kinase 8 (CDK8) partially suppresses the dwarfism and constitutive resistance phenotypes of camta1/2/3. CDK8 positively regulates steady‐state salicylic acid (SA) levels and systemic required resistance (SAR). The expression of SA biosynthesis genes such as ICS1 and EDS5 is down‐regulated in cdk8 mutants under uninfected conditions, suggesting that CDK8 contributes to the transcriptional regulation of these SA pathway genes. Knocking out another Mediator kinase module member MED12 yielded similar defects including decreased steady‐state SA level and compromised SAR, suggesting that the whole Mediator kinase module contributes to the transcriptional regulation of SA levels and SAR. Significance Statement: Knockout analysis of cdk8 and med12 mutants revealed that both mutants accumulate less defense hormone salicylic acid (SA), revealing the positive contribution of the kinase module of Mediator to the transcriptional regulation of SA accumulation and systemic acquired resistance (SAR). Such mechanisms helps us to better understand the complex regulatory roles of Mediator in plant immunity. [ABSTRACT FROM AUTHOR]

Plant cuticular wax is a heterogeneous mixture of very long chain fatty acids (VLCFAs) and their derivatives. Primary alcohols are the dominant wax components throughout leaf development of Brachypodium distachyon (Brachypodium). However, the genes involved in primary alcohol biosynthesis have not been investigated and their exact biological function remains unclear in Brachypodium to date. Here, we monitored the leaf wax profile and crystal morphology during Brachypodium leaf morphogenesis, and isolated three Brachypodium fatty acyl-CoA reductase (FAR) genes, named BdFAR1, BdFAR2 and BdFAR3, then analyzed their biochemical activities, substrate specificities, expression patterns, subcellular localization and stress induction. Transgenic expression of BdFAR genes in yeast (Saccharomyces cerevisiae), tomato (Solanum lycopersicum), Arabidopsis (Arabidopsis thaliana) and Brachypodium increased the production of primary alcohols. The three BdFAR genes were preferentially expressed in Brachypodium aerial tissues, consistent with known sites of wax primary alcohol deposition, and localized in the endoplasmic reticulum (ER) in Arabidopsis protoplasts. Finally, expression of the BdFAR genes was induced by drought, cold and ABA treatments, and drought stress significantly increased cuticular wax accumulation in Brachypodium. Taken together, these results indicate that the three BdFAR genes encode active FARs involved in the biosynthesis of Brachypodium wax primary alcohols and respond to abiotic stresses. [ABSTRACT FROM AUTHOR]