Genome-wide analysis of long non-coding RNAs unveils the regulatory roles in the heat tolerance of Chinese cabbage (Brassica rapa ssp.chinensis)

Long non-coding RNAs (lncRNAs) mediate important epigenetic regulation in various biological processes related to the stress response in plants. However, the systematic analysis of the lncRNAs expressed in Brassica rapa under heat stress has been elusive. In this study, we performed a genome-wide analysis of the lncRNA expression profiles in non-heading Chinese cabbage leaves using strand-specific RNA-sequencing. A total of 4594 putative lncRNAs were identified with a comprehensive landscape of dynamic lncRNA expression networks under heat stress. Co-expression networks of the interactions among the differentially expressed lncRNAs, mRNAs and microRNAs revealed that several phytohormones were associated with heat tolerance, including salicylic acid (SA) and brassinosteroid (BR) pathways. Of particular importance is the discovery of 25 lncRNAs that were highly co-expressed with 10 heat responsive genes. Thirty-nine lncRNAs were predicted as endogenous target mimics (eTMs) for 35 miRNAs, and five of them were validated to be involved in the heat tolerance of Chinese cabbage. Heat responsive lncRNA (TCONS_00048391) is an eTM for bra-miR164a, that could be a sponge for miRNA binding and may be a competing endogenous RNA (ceRNA) for the target gene NAC1 (Bra030820), affecting the expression of bra-miR164a in Chinese cabbage. Thus, these findings provide new insights into the functions of lncRNAs in heat tolerance and highlight a set of candidate lncRNAs for further studies in non-heading Chinese cabbage.