Genome-wide discovery and characterization of flower development related long non-coding RNAs in Prunus mume

Long non-coding RNAs (lncRNAs) are transcripts more than 200 bp in length do not encode proteins. Up to the present, it has been reported that lncRNAs play an essential role in developmental processes through their regulatory functions. However, their characteristics, expression inheritance patterns, and functions in Prunus mume are quite unidentified.

In this present study, we exposed the specific characters of pistil development process between single pistil cv 'Qingjia No.2' (QJN2) and multiple pistils cv 'Da Yu' (DY). We found that early October is the key stage for pistil differentiation. The similarity epidermis was observed between two types of pistil. We also further investigated a complete pistil development lncRNA profiles through RNA-seq in Prunus mume. 2572 unique lncRNAs and 24,648 genes mapped to Prunus mume genome, furthermore, 591 novel lncRNAs were predicted. Both unique lncRNAs and novel lncRNAs are shorter in length than the mRNAs, and the overall expression level of lncRNAs was lower than mRNAs in Prunus mume. 186 known lncRNAs, 1638 genes and 89 novel lncRNAs were identified as significant differential expressed in QJN2 compared with DY. We predicted 421 target genes of differentially expressed known lncRNAs (DEKLs) and 254 target genes of differentially expressed novel lncRNAs (DENLs). 153 miRNAs were predicted interacted with 100 DEKLs while 112 miRNAs were predicted interacted with 55 DENLs. Further analysis of the DEKLs showed that the lncRNA of XR_514690.2 down-regulated its target ppe-miR172d, and up-regulated AP2, respectively. Meanwhile, the other lncRNA of TCONS_00032517 induced cytokinin negative regulator gene A-ARR expression via repressing its target miRNA ppe-miR160a/b in DY. At the same time we found that the AP2 expression was significantly up-regulated by zeatin (ZT) treatment in flower buds. Our experiments suggest that the two lncRNAs of XR_514690.2 and TCONS_00032517 might contribute the formation of multiple pistils in Prunus mume.

This study shows the first characterization of lncRNAs involved in pistil development and provides new indications to elucidate how lncRNAs and their targets play role in pistil differentiation and flower development in Prunus mume.