The microRNA ppe-miR393 mediates auxin-induced peach fruit softening by promoting ethylene production

Abstract

Auxin can inhibit or promote fruit ripening, depending on the species. Melting flesh (MF) peach fruit (Prunus persica L. Batsch) cultivars produce high levels of ethylene caused by high concentrations of indole-3-acetic acid (IAA), which leads to rapid fruit softening at the late stage of development. In contrast, due to the low concentrations of IAA, the fruit of stony hard (SH) peach cultivars do not soften and produce little ethylene. Auxin seems necessary to trigger the biosynthesis of ethylene in peach fruit, however, the mechanism is not well understood. In this study, we identified miRNA gene family members ppe-miR393a and ppe-miR393b that are differentially expressed in SH and MF fruit. RNA ligase-mediated 5’ rapid amplification of cDNA ends and transient transformation of Nicotiana benthamiana revealed PpTIR1(TRANSPORT INHIBITOR RESPONSE 1), part of the auxin perception and response system, as a target of ppe-miR393a and b. Yeast two-hybrid assay and bimolecular fluorescence complementation assay revealed that PpTIR1 physically interacts with an Aux/IAA protein PpIAA13. The results of yeast one-hybrid assay, electrophoretic mobility shift assay and dual-luciferase assay indicated that PpIAA13 could directly bind to and trans-activate the promoter of PpACS1 (1-aminocyclopropane-1-carboxylic acid synthase 1), required for ethylene biosynthesis. Transient overexpression and suppression of ppe-miR393a and PpIAA13 in peach fruit induced and repressed the expression of PpACS1, confirming their regulatory role in ethylene synthesis. Gene expression analysis in developing MF and SH fruit, combined with postharvest α-Naphthalene acetic acid (NAA) treatment, supports a role for a ppe-miR393-PpTIR1-PpIAA13-PpACS1 module in regulating auxin-related differences in ethylene production and softening extent in different types of peach.

A Combinatorial TIR1-Aux/IAA Co-Receptor System for Peach Fruit Softening

“…It is hypothesized that PslTIR1 positively regulates auxin response and fruit set by mediating the degradation of Aux/IAA proteins, especially IAA9. In peaches, lower TIR1 protein levels trigger the stabilization of PpIAA13, leading to the accumulation of PpIAA13 protein, thus activating the expression of PpACS1 and promoting peach fruit softening [21]. In this study, we analyzed the expression of some auxin response genes and cell wall metabolic genes related to fruit firmness by transiently overexpressing the PpTIR1 gene in peach fruit.…”

“…The overexpression of the peach PpIAA19 (Ppa011935m) gene in tomatoes resulted in an increase in plant height, the number of lateral roots, and changes in parthenogenesis and fruit morphology [20]. The latest study showed that high levels of PpIAA13 (Ppa010871m) resulted in high expression of PpACS1, which increased ethylene production and peach fruit softening [21].…”