Small RNA and degradome profiling reveals important roles for microRNAs and their targets in tea plant response to drought stress.

Tea (Camellia sinensis) is a popular beverage worldwide. Drought stress (DS) is a major constraint on the growth, yield and quality of tea plants. MicroRNAs (miRNAs) play important roles in plant responses to DS. We constructed eight small RNA libraries from the drought-tolerant 'Ningzhou 2' (NZ2) and drought-susceptible 'Zhuyeqi' (ZYQ) cultivars during four stages [control (CK), the fourth day of DS, the eighth day of DS and after recovery (RC)]. A total of 268 conserved and 62 novel miRNAs were identified using small RNA sequencing. In total, 139 (52.9%) and 96 (36.0%) conserved miRNAs were differentially expressed during the four stages (P ≤ 0.05) in NZ2 and ZYQ, respectively. A total of 814 predicted target genes were identified as differentially regulated by 199 miRNAs through degradome sequencing. Among them, 201 and 218 genes were specific to the NZ2 and ZYQ cultivars, respectively, and 395 were common to both cultivars. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed the biological roles of these targets and showed that some of the targets responded to DS in a stress- and cultivar-dependent manner. Correlated expression patterns between miRNA and their targets showed that specific miRNAs target the miRNA effector Argonaute 1 (AGO1), drought signaling-related receptors and enzymes, transcription factors, and other structural and functional proteins. The predicted regulatory networks provide insights into a potential miRNA-mediated regulatory mechanism. These results will contribute to the breeding of drought-tolerant tea plants and to elucidating miRNA regulation in response to drought.