Formaldehyde-assisted isolation of regulatory DNA elements from Arabidopsis leaves

Heat stress causes chromatin accessibility and related gene expression changes in crown tissues of barley (Hordeum vulgare)

Plant responses to stress caused by high temperatures involve changes occurring at the molecular, metabolic, and physiological levels. Understanding the mechanisms by which plants recognize signals to activate this response is a prerequisite for identifying key genes and signaling pathways and for obtaining heat-tolerant plants. We demonstrated the first implementation of an assay for transposase-accessible chromatin to identify open chromatin regions (OCRs) in crown tissues of barley using three genotypes carrying different allelic forms of the sdw1 gene encoding gibberellin 20-oxidase subjected to elevated temperatures. In parallel, we performed gene expression analysis, which allowed us to relate changes in chromatin state to changes in transcriptional activity. The obtained data revealed that the hypersensitive chromatin regions within the genes were more repeatable than those outside the gene intervals. We observed that prolonged exposure to high temperatures increased chromatin accessibility. Genes with OCRs in their regulatory regions were involved in stress signaling and tolerance, including calcium-dependent protein kinase, mitogen-activated protein kinase (MAPK3), receptor-like cytoplasmic kinase (RLK), TIFY domain-containing transcriptional regulator, bZIP transcription factor, and regulatory protein NPR1. The effect of genotype on gene expression was not as pronounced as that of temperature. By combining results from the differential analysis of chromatin accessibility and expression profiles, we identified genes with high temperature-induced changes in chromatin accessibility associated with expression alterations. Importantly, our data revealed a relationship between the loss of chromatin accessibility in response to heat and the downregulation of genes related to gibberellin signaling.

Mind the gap: Epigenetic regulation of chromatin accessibility in plants

Chromatin plays a crucial role in genome compaction and is fundamental for regulating multiple nuclear processes. Nucleosomes, the basic building blocks of chromatin, are central in regulating these processes, determining chromatin accessibility by limiting access to DNA for various proteins and acting as important signaling hubs. The association of histones with DNA in nucleosomes and the folding of chromatin into higher-order structures are strongly influenced by a variety of epigenetic marks, including DNA methylation, histone variants, and histone post-translational modifications. Additionally, a wide array of chaperones and ATP-dependent remodelers regulate various aspects of nucleosome biology, including assembly, deposition, and positioning. This review provides an overview of recent advances in our mechanistic understanding of how nucleosomes and chromatin organization are regulated by epigenetic marks and remodelers in plants. Furthermore, we present current technologies for profiling chromatin accessibility and organization.

Marker and readout genes for defense priming in Pseudomonas cannabina pv. alisalensis interaction aid understanding systemic immunity in Arabidopsis

Following localized infection, the entire plant foliage becomes primed for enhanced defense. However, specific genes induced during defense priming (priming-marker genes) and those showing increased expression in defense-primed plants upon rechallenge (priming-readout genes) remain largely unknown. In our Arabidopsis thaliana study, genes AT1G76960 (function unknown), CAX3 (encoding a vacuolar Ca2+/H+ antiporter), and CRK4 (encoding a cysteine-rich receptor-like protein kinase) were strongly expressed during Pseudomonas cannabina pv. alisalensis-induced defense priming, uniquely marking the primed state for enhanced defense. Conversely, PR1 (encoding a pathogenesis-related protein), RLP23 and RLP41 (both encoding receptor-like proteins) were similarly activated in defense-primed plants before and after rechallenge, suggesting they are additional marker genes for defense priming. In contrast, CASPL4D1 (encoding Casparian strip domain-like protein 4D1), FRK1 (encoding flg22-induced receptor-like kinase), and AT3G28510 (encoding a P loop-containing nucleoside triphosphate hydrolases superfamily protein) showed minimal activation in uninfected, defense-primed, or rechallenged plants, but intensified in defense-primed plants after rechallenge. Notably, mutation in only priming-readout gene NHL25 (encoding NDR1/HIN1-like protein 25) impaired both defense priming and systemic acquired resistance, highlighting its previously undiscovered pivotal role in systemic plant immunity.

Epigenetics of wheat-rust interaction: an update

The outcome of different host-pathogen interactions is influenced by both genetic and epigenetic systems, which determine the response of plants to pathogens and vice versa. This review highlights key molecular mechanisms and conceptual advances involved in epigenetic research and the progress made in epigenetics of wheat-rust interactions. Epigenetics implies the heritable changes in the way of gene expression as a consequence of the modification of DNA bases, histone proteins, and/or non-coding-RNA biogenesis without disturbing the underlying nucleotide sequence. The changes occurring between DNA and its surrounding chromatin without altering its DNA sequence and leading to significant changes in the genome of any organism are called epigenetic changes. Epigenetics has already been used successfully to explain the mechanism of human pathogens and in the identification of pathogen-induced modifications within various host plants. Wheat rusts are one of the most vital fungal diseases throughout the major wheat-growing areas of the world. The epigenome in plant pathogens causing diseases such as wheat rusts is mysterious. The investigations of host and pathogen epigenetics in the wheat rusts system can offer a piece of suitable evidence for elucidation of the molecular basis of host-pathogen interaction. Besides, the information on the epigenetic regulation of the genes involved in resistance or pathogenicity will provide better insights into the complex resistance signaling pathways and could provide answers to certain key questions, such as whether epigenetic regulation of certain genes is imparting resistance to host in response of certain pathogen elicitors or not. In the last few years, there has been an upsurge in research on the host as well as pathogen epigenetics and its outcome in plant-pathogen interactions. This review summarizes the progress made in the areas related to the epigenetic control of host-pathogen interaction with particular emphasis on wheat rusts.

Subunits of the PBAP Chromatin Remodeler Are Capable of Mediating Enhancer-Driven Transcription in Drosophila

The chromatin remodeler SWI/SNF is an important participant in gene activation, functioning predominantly by opening the chromatin structure on promoters and enhancers. Here, we describe its novel mode of action in which SWI/SNF factors mediate the targeted action of an enhancer. We studied the functions of two signature subunits of PBAP subfamily, BAP170 and SAYP, in Drosophila. These subunits were stably tethered to a transgene reporter carrying the hsp70 core promoter. The tethered subunits mediate transcription of the reporter in a pattern that is generated by enhancers close to the insertion site in multiple loci throughout the genome. Both tethered SAYP and BAP170 recruit the whole PBAP complex to the reporter promoter. However, we found that BAP170-dependent transcription is more resistant to the depletion of other PBAP subunits, suggesting that BAP170 may play a more critical role in establishing enhancer-dependent transcription.

Priming for enhanced ARGONAUTE2 activation accompanies induced resistance to cucumber mosaic virus in Arabidopsis thaliana

Systemic acquired resistance (SAR) is a broad-spectrum disease resistance response that can be induced upon infection from pathogens or by chemical treatment, such as with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH). SAR involves priming for more robust activation of defence genes upon pathogen attack. Whether priming for SAR would involve components of RNA silencing remained unknown. Here, we show that upon leaf infiltration of water, BTH-primed Arabidopsis thaliana plants accumulate higher amounts of mRNA of ARGONAUTE (AGO)2 and AGO3, key components of RNA silencing. The enhanced AGO2 expression is associated with prior-to-activation trimethylation of lysine 4 in histone H3 and acetylation of histone H3 in the AGO2 promoter and with induced resistance to the yellow strain of cucumber mosaic virus (CMV[Y]). The results suggest that priming A. thaliana for enhanced defence involves modification of histones in the AGO2 promoter that condition AGO2 for enhanced activation, associated with resistance to CMV(Y). Consistently, the fold-reduction in CMV(Y) coat protein accumulation by BTH pretreatment was lower in ago2 than in wild type, pointing to reduced capacity of ago2 to activate BTH-induced CMV(Y) resistance. A role of AGO2 in pathogen-induced SAR is suggested by the enhanced activation of AGO2 after infiltrating systemic leaves of plants expressing a localized hypersensitive response upon CMV(Y) infection. In addition, local inoculation of SAR-inducing Pseudomonas syringae pv. maculicola causes systemic priming for enhanced AGO2 expression. Together our results indicate that defence priming targets the AGO2 component of RNA silencing whose enhanced expression is likely to contribute to SAR.