Tea oil camellia ( Camellia oleifera ), an important woody oil tree, is a source of seed oil of high nutritional and medicinal values and has been being widely planted in southern China. However, there is no report on the identification of miRNAs involved in lipid metabolism and seed development in high- and low-oil cultivars of tea oil camellia. Thus, we explored the roles of miRNAs in the critical period of oil formation and accumulation in tea oil camellia, and identified miRNA-mRNA regulatory modules involved in lipid metabolism and seed development.
Sixteen small RNA libraries for high- and low-oil cultivars of the critical period of oil biosynthesis were constructed. A total of 196 miRNAs, including 156 known miRNAs from 35 families and 40 novel miRNAs, were identified, and 55 significantly differentially expressed miRNAs were found, which included 34 up-regulated miRNAs and 21 down-regulated miRNAs. An integrated analysis of miRNA and mRNA transcriptome sequence data and qRT-PCR-based information was performed and revealed that nine miRNA-mRNA regulatory modules were related to lipid metabolism, such as the negative regulatory modules of ath-miR858b- MYB82 / MYB3 / MYB44 represses seed oil biosynthesis and a positive regulation module of csi-miR166e-5p- S-ACP - DES6 for formation and accumulation of oleic acid. Twenty-tree miRNA-mRNA regulatory modules were involved in the regulation of seed size, such as a negative regulatory module of hpe-miR162a_L-2- ARF19 involved in early seed development. Twelve miRNA-mRNA regulatory modules regulating growth and development were identified, such as the negative regulatory modules of han-miR156a_L+1- SPL4 / SBP2 promoting early seed development. The targeting relationship of the cpa-miR393_R-1-AFB2 regulatory module were verified by luciferase activity assays.
Multiple microRNAs (miRNAs) were identified to involve in developing seeds of tea oil camellia, especially discovering several miRNA-mRNA regulatory modules involving in seed development and lipid metabolism. These data provide important theoretical value and a scientific basis for the genetic improvement of new varieties of tea oil camellia in the future.