DNA methylation-associated epigenetic changes in stress tolerance of plants

Abstract

Plants require optimum environmental conditions to grow, develop, and reproduce. Abiotic and biotic stresses have direct, negative effects on the biochemical and physiological processes which is associated with plant growth and development. These processes, under stress conditions, are significantly modified to increase a plant's tolerance and to allow it to reproduce in the shortest possible time leads to escape or to minimize its exposure to unfavorable environmental conditions. As a consequence of these changes on its life cycle, a significant reduction in plant yield is expected. Plants have evolved several strategies to cope with environmental stresses which include expression level alteration of some genes through the introduction of epigenetic modifications, such as DNA methylation. DNA methylation plays a key role in gene expression by enhancing RNA-directed DNA methylation (RdDM) of genes and by inducing some histone modifications. Plants sometimes inherit their tolerance to stresses through the transmission of methylated genes from the parents. They may also produce new alleles by favoring homologous recombination at less methylated loci. However, sometimes this type of inheritance is not stable. DNA methylation may be significantly affected by the environment and cannot be experimentally manipulated or maintained. Therefore, extra care should be taken when designing strategies intended on producing plants with novel traits based on variations in DNA methylation. This chapter dealt with a brief account on epigenetic changes due to DNA methylation, histone modifications, and small RNA interference to modify gene expression pattern throughout the growth and developmental stages of plants to adjust different biotic and abiotic plants responses. The chapter will discuss also the possible use of genetic modifications to induce epigenetic changes that may improve plant traits, especially a plant's ability to grow under abiotic and biotic stresses, and will try to answer fundamental questions on how DNA methylation, chromatin alteration, and small RNA molecules control gene expression.