Small RNA and DNA Methylation of Tea Plants

Small RNAs are a category of short noncoding RNAs (ncRNAs) with 18–30 nt lengths. Based on their function and mechanisms of biogenesis, these small RNAs be classified into three major classes—microRNAs (miRNAs), heterochromatic small interfering RNAs (hc-siRNAs), as well as secondary small interfering RNAs (secondary siRNAs)—plus several other less well-characterized classes. Among them, miRNAs are a kind of small ncRNAs that are the main object of study in tea plants. They exhibit an essential role in regulating gene expression, primarily through cleavage at posttranscriptional and/or inhibition of translation of target mRNAs. Epigenetics is the mechanism for altering gene expression and phenotype without alterations in DNA sequence, and these changes can be transmitted continuously as cells divide in mitosis and meiosis. DNA methylation is one of the most common epigenetic modifications and is a crucial link between phenotype and genotype. Although many studies have been unraveled regarding the role of miRNAs and DNA methylation in diverse biological processes, such as maintenance of the functional integrity of genes and genome, regulating plant growth and development, metabolism, and coping with biotic and abiotic stresses, limited research has been carried out on their specific roles in tea plants, an area of inquiry with potentially significant and positive economic implications in tea. This chapter summarizes recent research advances on miRNA and DNA methylation in tea plants and discusses their regulatory functions in tea plant growth and development, metabolism, as well as adaptive responses to biotic and abiotic stresses, intending to shed light on the development of novel agronomic tools to improve tea quality.