Cauliflower mosaic virus P6 Dysfunctions Histone Deacetylase HD2C to Promote Virus Infection

NS1-mediated enhancement of MVC transcription and replication promoted by KAT5/H4K12ac

Histone modifications function in both cellular and viral gene expression. However, the roles of acetyltransferases and histone acetylation in parvoviral infection remain poorly understood. In the current study, we found the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), promoted the replication and transcription of parvovirus minute virus of canines (MVC). Notably, the expression of host acetyltransferases KAT5, GTF3C4, and KAT2A was increased in MVC infection, as well as H4 acetylation (H4K12ac). KAT5 is not only responsible for H4K12ac but also crucial for viral replication and transcription. The viral nonstructural protein NS1 interacted with KAT5 and enhanced its expression. Further study showed that Y44 in KAT5, which may be tyrosine-phosphorylated, is indispensable for NS1-mediated enhancement of KAT5 and efficient MVC replication. The data demonstrated that NS1 interacted with KAT5, which resulted in an enhanced H4K12ac level to promote viral replication and transcription, implying the epigenetic addition of H4K12ac in viral chromatin-like structure by KAT5 is vital for MVC replication.IMPORTANCEParvoviral genomes are chromatinized with host histones. Therefore, histone acetylation and related acetyltransferases are required for the virus to modify histones and open densely packed chromatin structures. This study illustrated that histone acetylation status is important for MVC replication and transcription and revealed a novel mechanism that the viral nonstructural protein NS1 hijacks the host acetyltransferase KAT5 to enhance histone acetylation of H4K12ac, which relies on a potential tyrosine phosphorylation site, Y44 in KAT5. Other parvoviruses share a similar genome organization and coding potential and may adapt a similar strategy for efficient viral replication and transcription.

Recent advancements in the role of histone acetylation dynamics to improve stress responses in plants

In eukaryotes, transcriptional regulation is determined by the DNA sequence and is facilitated through sophisticated and complex chromatin alterations and histone remodelling. Recent research has shown that the histone acetylation dynamic, an intermittent and reversible substitution, constitutes a prerequisite for chromatin modification. These changes in chromatin structure modulate genome-wide and specific changes in response to external and internal cues like cell differentiation, development, growth, light temperature, and biotic stresses. Histone acetylation dynamics also control the cell cycle. HATs and HDACs play a critical role in gene expression modulation during plant growth and response to environmental circumstances. It has been well established that HATs and HDACs interact with various distinct transcription factors and chromatin-remodelling proteins (CRPs) involved in the transcriptional regulation of several developmental processes. This review explores recent research on histone acyltransferases and histone deacetylases, mainly focusing on their involvement in plant biotic stress responses. Moreover, we also emphasized the research gaps that must be filled to fully understand the complete function of histone acetylation dynamics during biotic stress responses in plants. A thorough understanding of histone acetylation will make it possible to enhance tolerance against various kinds of stress and decrease yield losses in many crops.

Advances in Understanding the Mechanism of Cap-Independent Cucurbit Aphid-Borne Yellows Virus Protein Synthesis

Non-canonical translation mechanisms have been described for many viral RNAs. In the case of several plant viruses, their protein synthesis is controlled by RNA elements in their genomic 3'-ends that are able to enhance cap-independent translation (3'-CITE). The proposed general mechanism of 3'-CITEs includes their binding to eukaryotic translation initiation factors (eIFs) that reach the 5'-end and AUG start codon through 5'-3'-UTR-interactions. It was previously shown that cucurbit aphid-borne yellows virus (CABYV) has a 3'-CITE, which varies in sequence and structure depending on the phylogenetic group to which the isolate belongs, possibly as a result of adaptation to the different geographical regions. In this work, the cap-independent translation mechanisms of two CABYV 3'-CITEs belonging to the Mediterranean (CMTE) and Asian (CXTE) groups, respectively, were studied. In vivo cap-independent translation assays show that these 3'-CITEs require the presence of the CABYV short genomic 5'-UTR with at least 40% adenines in cis and an accessible 5'-end for its activity. Additionally, they suggest that the eIF4E-independent CABYV 3'-CITE activities may not require either eIF4A or the eIF4F complex, but may depend on eIF4G and PABP. By pulling down host proteins using RNA baits containing both 5'- and 3'-CABYV-UTRs, 80 RNA binding proteins were identified. These interacted preferentially with either CMTE, CXTE, or both. One of these proteins, specifically interacting with the RNA containing CMTE, was HSP70.2. Preliminary results suggested that HSP70.2 may be involved in CMTE- but not CXTE-mediated cap-independent translation activity.

Cauliflower mosaic virus disease spectrum uncovers novel susceptibility factor NCED9 in Arabidopsis thaliana

Viruses are intimately linked with their hosts and especially dependent on gene-for-gene interactions to establish successful infections. On the host side, defence mechanisms such as tolerance and resistance can occur within the same species, leading to differing virus accumulation in relation to symptomology and plant fitness. The identification of novel resistance genes against viruses and susceptibility factors is an important part of understanding viral patho-genesis and securing food production. The model plant Arabidopsis thaliana displays a wide symptom spectrum in response to RNA virus infections, and unbiased genome-wide association studies have proven a powerful tool to identify novel disease-genes. In this study we infected natural accessions of A. thaliana with the pararetrovirus cauliflower mosaic virus (CaMV) to study the phenotypic variations between accessions and their correlation with virus accumulation. Through genome-wide association mapping of viral accumulation differences, we identified several susceptibility factors for CaMV, the strongest of which was the abscisic acid synthesis gene NCED9. Further experiments confirmed the importance of abscisic acid homeostasis and its disruption for CaMV disease.

Epigenetic regulation of plant immunity: from chromatin codes to plant disease resistance

Facing a deteriorating natural environment and an increasing serious food crisis, bioengineering-based breeding is increasing in importance. To defend against pathogen infection, plants have evolved multiple defense mechanisms, including pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). A complex regulatory network acts downstream of these PTI and ETI pathways, including hormone signal transduction and transcriptional reprogramming. In recent years, increasing lines of evidence show that epigenetic factors act, as key regulators involved in the transcriptional reprogramming, to modulate plant immune responses. Here, we summarize current progress on the regulatory mechanism of DNA methylation and histone modifications in plant defense responses. In addition, we also discuss the application of epigenetic mechanism-based resistance strategies in plant disease breeding.

Genome-wide analysis of epigenetic and transcriptional changes in the pathogenesis of RGSV in rice

Rice grassy stunt virus (RGSV), a typical negative single-stranded RNA virus, invades rice and generates several disease signs, including dwarfing, tillering, and sterility. Previous research has revealed that RGSV-encoded proteins can force the host's ubiquitin-proteasome system to utilize them for viral pathogenesis. However, most of the studies were limited to a single omics level and lacked multidimensional data collection and correlation analysis on the mechanisms of RGSV-rice interactions. Here, we performed a comprehensive association analysis of genome-wide methylation sequencing, transcriptome sequencing, and histone H3K9me3 modification in RGSV-infested as well as non-infested rice leaves, and the levels of all three cytosine contexts (CG, CHG and CHH) were found to be slightly lower in RGSV-infected rice leaves than in normal rice. Large proportions of DMRs were distributed in the promoter and intergenic regions, and most DMRs were enriched in the CHH context, where the number of CHH hypo-DMRs was almost twice as high as that of hyper-DMRs. Among the genes with down-regulated expression and hypermethylation, we analyzed and identified 11 transcripts involved in fertility, plant height and tillering, and among the transcribed up-regulated and hypermethylated genes, we excavated 7 transcripts related to fertility, plant height and tillering. By analyzing the changes of histone H3K9me3 modification before and after virus infestation, we found that the distribution of H3K9me3 modification in the whole rice genome was prevalent, mainly concentrated in the gene promoter and gene body regions, which was distinctly different from the characteristics of animals. Combined with transcriptomic data, H3K9me3 mark was found to favor targeting highly expressed genes. After RGSV infection, H3K9me3 modifications in several regions of CTK and BR hormone signaling-related genes were altered, providing important targets for subsequent studies.

Histone modification and chromatin remodeling in plant response to pathogens

As sessile organisms, plants are constantly exposed to changing environments frequently under diverse stresses. Invasion by pathogens, including virus, bacterial and fungal infections, can severely impede plant growth and development, causing important yield loss and thus challenging food/feed security worldwide. During evolution, plants have adapted complex systems, including coordinated global gene expression networks, to defend against pathogen attacks. In recent years, growing evidences indicate that pathogen infections can trigger local and global epigenetic changes that reprogram the transcription of plant defense genes, which in turn helps plants to fight against pathogens. Here, we summarize up plant defense pathways and epigenetic mechanisms and we review in depth current knowledge's about histone modifications and chromatin-remodeling factors found in the epigenetic regulation of plant response to biotic stresses. It is anticipated that epigenetic mechanisms may be explorable in the design of tools to generate stress-resistant plant varieties.

Cross-Talk of Protein Expression and Lysine Acetylation in Response to TMV Infection in Nicotiana benthamiana

Lysine acetylation (K^ac), a reversible PTM, plays an essential role in various biological processes, including those involving metabolic pathways, pathogen resistance, and transcription, in both prokaryotes and eukaryotes. TMV, the major factor that causes the poor quality of Solanaceae crops worldwide, directly alters many metabolic processes in tobacco. However, the extent and function of K^ac during TMV infection have not been determined. The validation test to detect K^ac level and viral expression after TMV infection and Nicotinamide (NAM) treatment clarified that acetylation was involved in TMV infection. Furthermore, we comprehensively analyzed the changes in the proteome and acetylome of TMV-infected tobacco (Nicotiana benthamiana) seedlings via LC-MS/MS in conjunction with highly sensitive immune-affinity purification. In total, 2082 lysine-acetylated sites on 1319 proteins differentially expressed in response to TMV infection were identified. Extensive bioinformatic studies disclosed changes in acetylation of proteins engaged in cellular metabolism and biological processes. The vital influence of K^ac in fatty acid degradation and alpha-linolenic acid metabolism was also revealed in TMV-infected seedlings. This study first revealed K^ac information in N. benthamiana under TMV infection and expanded upon the existing landscape of acetylation in pathogen infection.