Micrornas Involved in Wounding-Mediated Pathway in Tomato

MicroRNAs (miRNAs) are an important class of endogenous small RNAs that modulate gene expression at the post-transcription level in both animals and plants. There has been a surge of interest in the past decade in identifying miRNAs and exploring their functions. It is well-established that miRNAs are involved in almost all activities during life cycle such as transitions between developmental stages and responses to environmental challenges. Systemin, an 18 amino acid polypeptide processed from its precursors, prosystemin, is a plant hormone  that mediates the wound response in the Solanaceae family.

By parsing deeply sequenced small RNA libraries, we identified over 150 high confident miRNAs in tomato. Meanwhile, the deep sequencing data indicates that around half of these miRNAs are expressed differently in wild type (WT) plants and plants over-expressed prosystemin (PS), which is confirmed by further molecular experiments.  Combined with the phenotypic changes in PS plants such as late flowering, less serrated leaves, more trichomes in stem, etc., we suspected that these changes might be caused by expression variation of miRNAs. We chose miR157 as an example which is one of the highest expressed miRNAs and significantly increased in PS plants compared to WT. Over-expressing miR157 in WT plants delayed the flowering time as in PS plants, and induced the expression of several defense genes, which suggests miR157 is involved in systemin-mediated wounding pathway.

Our experiments uncovered that increasing systemin could dramatically influence the expression of miRNA pool in tomato, and that in turn, miRNAs as an effector, are immensely involved in wounding pathway.