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The flesh color of pummelo (Citrus maxima) fruits is highly diverse and largely depends on the level of carotenoids, which are beneficial to human health. It is vital to investigate the regulatory network of carotenoid biosynthesis to improve the carotenoid content in pummelo. However, the molecular mechanism underlying carotenoid accumulation in pummelo is not fully understood. In this study, we identified a novel histone methyltransferase gene, CgSDG40, involved in carotenoid regulation by analyzing the flesh transcriptome of typical white-fleshed pummelo, red-fleshed pummelo and extreme-colored F1 hybrids from a segregated pummelo population. Expression of CgSDG40 corresponded to flesh color change and was highly coexpressed with CgPSY1. Interestingly, CgSDG40 and CgPSY1 are located physically adjacent to each other on the chromosome in opposite directions, sharing a partially overlapping promoter region. Subcellular localization analysis indicated that CgSDG40 localizes to the nucleus. Overexpression of CgSDG40 significantly increased the total carotenoid content in citrus calli relative to that in wild type. In addition, expression of CgPSY1 was significantly activated in overexpression lines relative to wild type. Taken together, our findings reveal a novel histone methyltransferase regulator, CgSDG40, involved in the regulation of carotenoid biosynthesis in citrus and provide new strategies for molecular design breeding and genetic improvement of fruit color and nutritional quality.

Plant pathogens secrete effector proteins to overcome host immunity and promote colonization. In oomycete plant pathogens, the expression of many effector genes is altered upon infection; however, the regulatory mechanisms are unclear. In this study, we identified a su(var)3–9, enhancer of zeste, and trithorax (SET) domain protein‐encoding gene, PsKMT3, that was highly induced at early infection stages in Phytophthora sojae. Deletion of PsKMT3 led to asexual development and pathogenicity defects. Chromatin immunoprecipitation followed by sequencing (ChIP‐seq) and western blot analyses demonstrated that histone H3K36 trimethylation (H3K36me3) was significantly reduced genome‐wide in mutants. RNA‐seq analysis identified 374 genes encoding secreted proteins that were differentially expressed in pskmt3 at the mycelium stage. The significantly altered genes encompassed the RxLR (Arg‐x‐Lys‐Arg) effector gene family, including the essential effector genes Avh23, Avh181, Avh240, and Avh241. Transcriptome analysis at early infection stages showed misregulation of effector gene expression waves in pskmt3. H3K36me3 was directly and indirectly associated with RxLR effector gene activation. Our results reveal a role of a SET domain protein in regulating effector gene expression and modulating histone methylation in P. sojae. [ABSTRACT FROM AUTHOR]

In plants, RNA-directed DNA methylation (RdDM) and related transcriptional gene silencing (TGS) involve members of the suppressor of variegation 3-9-homologous (SUVH) group of putative histone methyltransferases. Utilizing a reverse genetic approach in Arabidopsis thaliana, we demonstrate that two closely related SUVH members, SUVH2 and SUVH9, act partially non-redundant in RdDM. DNA methylation, transcript accumulation and association with histone modifications were analyzed at the endogenous RdDM target AtSN1 (a SINE-like retroelement) in suvh2 and suvh9 single as well as suvh2 suvh9 double mutants. SUVH2 was found to be required for full DNA methylation at AtSN1 in early seed development and was also higher expressed in seeds than at later developmental stages. SUVH9 had its impact on RdDM later during vegetative development of the plant and was also higher expressed during that stage than at earlier developmental stages. The strongest reduction of RdDM at AtSN1 was found in suvh2 suvh9 double mutant plants. Histone 3-lysine 9-dimethylation (H3K9me2) associated with AtSN1 was reduced only in the simultaneous absence of functional SUVH2 and SUVH9. Thus, SUVH2 and SUVH9 functions in RdDM and TGS are overlapping in spite of some developmental specialization. Pol V specific transcripts were reduced in suvh2 suvh9 plants. This might indicate a role of these SUVH proteins in Pol V complex recruitment. [ABSTRACT FROM AUTHOR]

Abstract: Post-translational methylation of lysine residues on histone tails is an epigenetic modification crucial for regulation of chromatin structure and gene expression in eukaryotes. The majority of the histone lysine methyltransferases (HKMTases) conferring such modifications are proteins with a conserved SET domain responsible for the enzymatic activity. The SET domain proteins in the model plant Arabidopsis thaliana can be assigned to evolutionarily conserved classes with different specificities allowing for different outcomes on chromatin structure. Here we review the present knowledge of the biochemical and biological functions of plant SET domain proteins in developmental processes. This article is part of a Special Issue entitled: Epigenetic control of cellular and developmental processes in plants. [Copyright &y& Elsevier]

Histone methylation plays a fundamental role in regulating diverse developmental processes and is also involved in silencing repetitive sequences in order to maintain genome stability. The methylation marks are written on lysine or arginine by distinct enzymes, namely, histone lysine methyltransferases (HKMTs) or protein arginine methyltransferases (PRMTs). Once established, the methylation marks are specifically recognized by the proteins that act as readers and are interpreted into specific biological outcomes. Histone methylation status is dynamic; methylation marks can be removed by eraser enzymes, the histone demethylases (HDMs). The proteins responsible for writing, reading, and erasing the methylation marks are known mostly in animals. During the past several years, a growing body of literature has demonstrated the impact of histone methylation on genome management, transcriptional regulation, and development in plants. The aim of this review is to summarize the biochemical, genetic, and molecular action of histone methylation in two plants, the dicot Arabidopsis and the monocot rice. [ABSTRACT FROM AUTHOR]

Abstract: Histone methylation plays crucial roles in epigenetic regulation. The SET domain proteins are now recognized as generally having methyltransferase activity targeted to specific lysine residues of histones. The enzymes and their specific histone lysine methylation have enormous impacts on the regulation of chromatin structure and function. In this review, we discuss recent advances made on histone lysine methylations and their diverse functions in plant growth and development. [Copyright &y& Elsevier]