MicroRNAs in Pyrus stigma tissue and stigma exudates

In many plant species, flower stigma secretions are important in early stages of sexual reproduction. Previous chemical analysis and proteomic characterization of these exudates provided insights into their biological function. Nevertheless, the presence of nucleic acids in the stigma exudates has not been previously reported. Here we studied the stigma exudates of Pyrus communis, Pyrus pyrifolia and Pyrus syriaca, and showed them to harbor extracellular RNAs of various sizes. RNA sequencing revealed, for the first time, the presence of known Rosaceae mature micro-RNAs (miRs), also abundant in the stigma source tissue. Predicted targets of the exudate miRs in the Arabidopsis thaliana genome include genes involved in various biological processes. Several of these genes are pollen transcribed, suggesting possible involvement of exudate miRs in transcriptional regulation of the pollen. Moreover, extracellular miRs can potentially act across kingdoms and target genes of stigma interacting organisms/microorganisms, thus opening novel applicative avenues in HortSciences. Stigma tissue and stigma exudates were collected from 2 independent pooled flowers of Pyrus pyrifolia, a single pool of Pyrus communis flowers, and 3 independent pools of Pyrus syriaca flowers. Small RNAs were purified and sequenced using Illumina technology.