Epigenetic regulation in plant abiotic stress responses

In eukaryotic cells, gene expression is greatly influenced by the dynamic chromatin environment. Epigenetic mechanisms, including covalent modifications to DNA and histone tails and the accessibility of chromatin, create various chromatin states for stress‐responsive gene expression that is important for adaptation to harsh environmental conditions. Recent studies have revealed that many epigenetic factors participate in abiotic stress responses, and various chromatin modifications are changed when plants are exposed to stressful environments. In this review, we summarize recent progress on the cross‐talk between abiotic stress response pathways and epigenetic regulatory pathways in plants. Our review focuses on epigenetic regulation of plant responses to extreme temperatures, drought, salinity, the stress hormone abscisic acid, nutrient limitations and ultraviolet stress, and on epigenetic mechanisms of stress memory.     

Chromatin modifications and remodeling in plant abiotic stress responses

Sensing environmental changes and initiating a gene expression response are important for plants as sessile autotrophs. The ability of epigenetic status to alter rapidly and reversibly could be a key component to the flexibility of plant responses to the environment. The involvement of epigenetic mechanisms in the response to environmental cues and to different types of abiotic stresses has been documented. Different environmental stresses lead to altered methylation status of DNA as well as modifications of nucleosomal histones. Understanding how epigenetic mechanisms are involved in plant response to environmental stress is highly desirable, not just for a better understanding of molecular mechanisms of plant stress response but also for possible application in the genetic manipulation of plants. In this review, we highlight our current understanding of the epigenetic mechanisms of chromatin modifications and remodeling, with emphasis on the roles of specific modification enzymes and remodeling factors in plant abiotic stress responses. This article is part of a Special Issue entitled: Plant gene regulation in response to abiotic stress.     

植物中表观遗传修饰研究进展

表观遗传是指DNA序列不发生变化, 但基因表达发生了可遗传的改变, 主要涉及DNA与染色体上的一些可逆修饰以及一些转录调控机制。DNA甲基化、组蛋白修饰和非编码RNA调控是表观遗传学研究的三大支柱。三者在植物生长发育、应对生物和非生物胁迫以及适应环境变化中发挥着极其重要的作用。该文综述了植物中DNA甲基化、组蛋白修饰、非编码RNA调控的研究进展及其对植物株高、生育期、花型、果实着色以及应对环境胁迫等方面的影响。     

Retrospective and perspective of plant epigenetics in China

Epigenetics refers to the study of heritable changes in gene function that do not involve changes in the DNA sequence. Such effects on cellular and physiological phenotypic traits may result from external or environmental factors or be part of normal developmental program. In eukaryotes, DNA wraps on a histone octamer (two copies of H2A, H2B, H3 and H4) to form nucleosome, the fundamental unit of chromatin. The structure of chromatin is subjected to a dynamic regulation through multiple epigenetic mechanisms, including DNA methylation, histone posttranslational modifications (PTMs), chromatin remodeling and noncoding RNAs. As conserved regulatory mechanisms in gene expression, epigenetic mechanisms participate in almost all the important biological processes ranging from basal development to environmental response. Importantly, all of the major epigenetic mechanisms in mammalians also occur in plants. Plant studies have provided numerous important contributions to the epigenetic research. For example, gene imprinting, a mechanism of parental allele-specific gene expression, was firstly observed in maize; evidence of paramutation, an epigenetic phenomenon that one allele acts in a single locus to induce a heritable change in the other allele, was firstly reported in maize and tomato. Moreover, some unique epigenetic mechanisms have been evolved in plants. For example, the 24-nt siRNA-involved RNA-directed DNA methylation (RdDM) pathway is plant-specific because of the involvements of two plant-specific DNA-dependent RNA polymerases, Pol IV and Pol V. A thorough study of epigenetic mechanisms is of great significance to improve crop agronomic traits and environmental adaptability. In this review, we make a brief summary of important progress achieved in plant epigenetics field in China over the past several decades and give a brief outlook on future research prospects. We focus our review on DNA methylation and histone PTMs, the two most important aspects of epigenetic mechanisms.     

Epigenetic and small RNA regulation of senescence

Leaf senescence is regulated through a complex regulatory network triggered by internal and external signals for the reprogramming of gene expression. In plants, the major developmental phase transitions and stress responses are under epigenetic control. In this review, the underlying molecular mechanisms are briefly discussed and evidence is shown that epigenetic processes are also involved in the regulation of leaf senescence. Changes in the chromatin structure during senescence, differential histone modifications determining active and inactive sites at senescence-associated genes and DNA methylation are addressed. In addition, the role of small RNAs in senescence regulation is discussed.