https://www.cell.com/trends/plant-science/pdf/S1360-1385(10)00032-4.pdf

WRKY transcription factors.

Dynasore, a Cell-Permeable Inhibitor of Dynamin

WRKY transcription factors are one of the largest families of transcriptional regulators found exclusively in plants. They have diverse biological functions in plant disease resistance, abiotic stress responses, nutrient deprivation, senescence, seed and trichome development, embryogenesis, as well as additional developmental and hormone-controlled processes. WRKYs can act as transcriptional activators or repressors, in various homo- and heterodimer combinations. Here we review recent progress on the function of WRKY transcription factors in Arabidopsis and other plant species such as rice, potato, and parsley, with a special focus on abiotic, developmental, and hormone-regulated processes.

https://www.tandfonline.com/doi/pdf/10.4161/psb.27700

WRKY transcription factors: Jack of many trades in plants

Plants in their natural habitat have to face multiple stresses simultaneously. Evolutionary adaptation of developmental, physiological, and biochemical parameters give advantage over a single window of stress but not multiple. On the other hand transcription factors like WRKY can regulate diverse responses through a complicated network of genes. So molecular orchestration of WRKYs in plant may provide the most anticipated outcome of simultaneous multiple responses. Activation or repression through W-box and W-box like sequences is regulated at transcriptional, translational, and domain level. Because of the tight regulation involved in specific recognition and binding of WRKYs to downstream promoters, they have become promising candidate for crop improvement. Epigenetic, retrograde and proteasome mediated regulation enable WRKYs to attain the dynamic cellular homeostatic reprograming. Overexpression of several WRKYs face the paradox of having several beneficial affects but with some unwanted traits. These overexpression-associated undesirable phenotypes need to be identified and removed for proper growth, development and yeild. Taken together, we have highlighted the diverse regulation and multiple stress response of WRKYs in plants along with the future prospects in this field of research.

/pdf/wrky-transcription-factors-molecular-regulation-and-stress-2cpccsr1cr.pdf

WRKY Transcription Factors: Molecular Regulation and Stress Responses in Plants.

Plants inhabit environments crowded with infectious microbes that pose constant threats to their survival. Necrotrophic pathogens are notorious for their aggressive and wide-ranging virulence strategies that promote host cell death and acquire nutrients for growth and reproduction from dead cells. This lifestyle constitutes the axis of their pathogenesis and virulence strategies and marks contrasting immune responses to biotrophic pathogens. The diversity of virulence strategies in necrotrophic species corresponds to multifaceted host immune response mechanisms. When effective, the plant immune system disarms the infectious necrotroph of its pathogenic arsenal or attenuates its effect, restricting further ingress and disease symptom development. Simply inherited resistance traits confer protection against host-specific necrotrophs (HSNs), whereas resistance to broad host-range necrotrophs (BHNs) is complex. Components of host genetic networks, as well as the molecular and cellular processes that mediate host immune responses to necrotrophs, are being identified. In this review, recent advances in our understanding of plant immune responses to necrotrophs and comparison with responses to biotrophic pathogens are summarized, highlighting common and contrasting mechanisms.

Plant Immunity to Necrotrophs

Leaf senescence, the final step of leaf development, involves extensive reprogramming of gene expression. Here, we show that these processes include discrete changes of epigenetic indexing, as well as global alterations in chromatin organization. During leaf senescence, the interphase nuclei show a decondensation of chromocenter heterochromatin, and changes in the nuclear distribution of the H3K4me2, H3K4me3, and the H3K27me2 and H3K27me3 histone modification marks that index active and inactive chromatin, respectively. Locus-specific epigenetic indexing was studied at the WRKY53 key regulator of leaf senescence. During senescence, when the locus becomes activated, H3K4me2 and H3K4me3 are significantly increased at the 5' end and at coding regions. Impairment of these processes is observed in plants overexpressing the SUVH2 histone methyltransferase, which causes ectopic heterochromatization. In these plants the transcriptional initiation of WRKY53 and of the senescence-associated genes SIRK, SAG101, ANAC083, SAG12 and SAG24 is inhibited, resulting in a delay of leaf senescence. In SUVH2 overexpression plants, significant levels of H3K27me2 and H3K27me3 are detected at the 5'-end region of WRKY53, resulting in its transcriptional repression. Furthermore, SUVH2 overexpression inhibits senescence-associated global changes in chromatin organization. Our data suggest that complex epigenetic processes control the senescence-specific gene expression pattern.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0960-7412.2009.03782.x

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana.

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana: Epigenetic control of leaf senescence

Senescence processes are part of the plant developmental programme. They involve reprogramming of gene expression and are under the control of a complex regulatory network closely linked to other developmental and stressresponsive pathways. Recent evidence indicates that leaf senescence is regulated via epigenetic mechanisms. In the present review, the epigenetic control of plant senescence is discussed in the broader context of environmentsensitive plant development. The review outlines the concept of epigenetic control of interconnected regulatory pathways steering stress responses and plant development. Besides giving an overview of techniques used in the field, it summarizes recent findings on global alterations in chromatin structure, histone and DNA modifications, and ATPdependent chromatin remodelling during plant senescence and linked processes.

/pdf/epigenetic-control-of-plant-senescence-and-linked-processes-ipumowptdb.pdf

Epigenetic control of plant senescence and linked processes

Leaf senescence is the final developmental stage of a leaf. The progression of barley primary leaf senescence was followed by measuring the senescence-specific decrease in chlorophyll content and photosystem II efficiency. In order to isolate novel factors involved in leaf senescence, a differential display approach with mRNA populations from young and senescing primary barley leaves was applied. In this approach, 90 senescence up-regulated cDNAs were identified. Nine of these clones were, after sequence analyses, further characterized. The senescence-associated expression was confirmed by Northern analyses or quantitative RealTime-PCR. In addition, involvement of the phytohormones ethylene and abscisic acid in regulation of these nine novel senescence-induced cDNA fragments was investigated. Two cDNA clones showed homologies to genes with a putative regulatory function. Two clones possessed high homologies to barley retroelements, and five clones may be involved in degradation or transport processes. One of these genes was further analysed. It encodes an ADP ribosylation factor 1-like protein (HvARF1) and includes sequence motifs representing a myristoylation site and four typical and well conserved ARF-like protein domains. The localization of the protein was investigated by confocal laser scanning microscopy of onion epidermal cells after particle bombardment with chimeric HvARF1-GFP constructs. Possible physiological roles of these nine novel SAGs during barley leaf senescence are discussed.

Identification and characterization of novel senescence-associated genes from barley (Hordeum vulgare) primary leaves.

Leaf senescence involves extensive reprogramming of gene expression effectuating the complex biochemical and structural changes that occur during the last stage of leaf development. In a large-scale transcriptomic approach in Arabidopsis thaliana (L.) Heynh., using qRT-PCR, gene expression for more than 380 transcriptional regulators was shown to be regulated in a senescence-specific manner. Overexpression of SUVH2 histone methyltransferase, which was previously reported by Ay and others (Plant J 58:333–346, 2009) to delay leaf senescence, affected gene expression of about 50 % of these senescence-related regulatory factors (SRRFs), whereas the other half was regulated during senescence similar to wild type. Thereby, the senescence-related transcription factor families AP2-EREBP, C2H2, NAC, and WRKY are affected most notably. This suggests a direct or indirect locus-specific mode of SUVH2 action. Interestingly, we found that 45 of the identified SRRFs possess an ERF-associated amphiphilic repression motif, indicating that EAR motif-mediated transcriptional repression could be a principal mechanism within regulation of senescence. Furthermore, about 30 % of the SRRFs are predicted as putative targets of the ELONGATED HYPOCOTYL5 (HY5) bZIP transcription factor. This suggests that HY5-dependent processes play an important role within the regulatory network of leaf senescence. Moreover, these processes seem to be specifically affected in plants overexpressing SUVH2. Our results give new insights into the complex regulatory network of senescence-associated processes and the specific involvement of chromatin alterations.

Nicole Ay

Papers

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana.

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana: Epigenetic control of leaf senescence

Epigenetic control of plant senescence and linked processes

Identification and characterization of novel senescence-associated genes from barley (Hordeum vulgare) primary leaves.

Regulatory Factors of Leaf Senescence are Affected in Arabidopsis Plants Overexpressing the Histone Methyltransferase SUVH2