SummaryWRKY transcription factors (TFs) are key regulators of many plant processes, including the responses to biotic and abiotic stresses, senescence, seed dormancy and seed germination. For over 15 years, limited evidence has been available suggesting that WRKY TFs may play roles in regulating plant responses to the phytohormone abscisic acid (ABA), notably some WRKY TFs are ABA-inducible repressors of seed germination. However, the roles of WRKY TFs in other aspects of ABA signalling, and the mechanisms involved, have remained unclear. Recent significant progress in ABA research has now placed specific WRKY TFs firmly in ABA-responsive signalling pathways, where they act at multiple levels. In Arabidopsis, WRKY TFs appear to act downstream of at least two ABA receptors: the cytoplasmic PYR ⁄ PYL ⁄ RCARprotein phosphatase 2C-ABA complex and the chloroplast envelope-located ABAR-ABA complex. In vivo and in vitro promoter-binding studies show that the target genes for WRKY TFs that are involved in ABA signalling include well-known ABA-responsive genes such as ABF2, ABF4, ABI4, ABI5, MYB2, DREB1a, DREB2a and RAB18. Additional well-characterized stressinducible genes such as RD29A and COR47 are also found in signalling pathways downstream of WRKY TFs. These new insights also reveal that some WRKY TFs are positive regulators of ABA-mediated stomatal closure and hence drought responses. Conversely, many WRKY TFs are negative regulators of seed germination, and controlling seed germination appears a common function of a subset of WRKY TFs in flowering plants. Taken together, these new data demonstrate that WRKY TFs are key nodes in ABA-responsive signalling networks.

Studies of promoters that largely regulate gene expression at the transcriptional level are crucial for improving our basic understanding of gene regulation and will expand the toolbox of available promoters for use in plant biotechnology. In this review, we present a comprehensive analysis of promoters and their underlying mechanisms in transcriptional regulation, including epigenetic marks and chromatin-based regulation. Large-scale prediction of promoter sequences and their contributing cis-acting elements has become routine due to recent advances in transcriptomic technologies and genome sequencing of several plants. However, predicted regulatory sequences may or may not be functional and demonstration of the contribution of the element to promoter activity is essential for confirmation of regulatory sequences. Synthetic promoters and introns provide useful approaches for functional validation of promoter sequences. The development and improvement of gene expression tools for rapid, efficient, predictable, and high-throughput analysis of promoter components will be critical for confirmation of the functional regulatory element sequences identified through transcriptomic and genomic analyses.

Processing bodies (PBs) are specialized cytoplasmic foci where mRNA turnover and translational repression can take place. Stress granules are related cytoplasmic foci. The CCCH tandem zinc finger proteins (TZFs) play pivotal roles in gene expression, cell fate specification, and various developmental processes. Human TZF binds AU-rich elements at the 3# untranslated region and recruits decapping, deadenylation, and exonucleolytic enzymes to PBs for RNA turnover. Recent genetic studies indicate that plant TZFs are involved in gene regulation and hormone-mediated environmental responses. It is unknown if plant TZFs can bind RNA and be localized to PBs or stress granules. The Arabidopsis (Arabidopsis thaliana) AtTZF1/AtCTH/AtC3H23 was identified as a sugar-sensitive gene in a previous microarray study. It is characterized by a TZF motif that is distinct from the human TZF. Higher plants such as Arabidopsis and rice (Oryza sativa) each have a gene family containing this unique TZF motif. Here, we show that AtTZF1 can traffic between the nucleus and cytoplasmic foci. AtTZF1 colocalizes with markers of PBs, and the morphology of these cytoplasmic foci resembles that of mammalian PBs and stress granules. AtTZF1-associated cytoplasmic foci are dynamic and tissue specific. They can be induced by dark and wound stresses and are preferentially present in actively growing tissues and stomatal precursor cells. Since AtTZF1 can bind both DNA and RNA in vitro, it raises the possibility that AtTZF1 might be involved in DNA and/or RNA regulation.