The Aux/IAA Factor PbIAA.C3 Positively Regulates Ethylene Biosynthesis During Pear Fruit Ripening by Activating the PbACS1b Transcription

Phytohormone ethylene is one of the important plant hormones that regulate fruit development and ripening. The transcription regulation of ethylene biosynthesis has been extensively studied in fleshy fruit, but the role of auxin/indole-3-acetic acid (Aux/IAA) in ethylene biosynthesis is still unknown. In this study, based on the genome-wide expression analyses of pear Aux/IAA genes, we found that PbIAA.C3 had a higher expression level in ripening fruits than in developing fruits in all 13 tested pear cultivars. Over-expression of PbIAA.C3 increased ethylene production, while silencing of PbIAA.C3 decreased ethylene production in pear fruit. This result indicates that PbIAA.C3 positively regulates ethylene biosynthesis during fruit ripening. Dual-luciferase assay showed that PbIAA.C3 could enhance the activity of the 1-aminocyclopropane1-carboxylate synthase PbACS1b expression by binding to the upstream region from − 2000 to − 1500 bp of the initiation codon of PbACS1b to increase the expression level. However, the transcription activation of PbIAA.C3 was repressed by the auxin-responsive factor PbARF32 which physically interacted with PbIAA.C3. Therefore, PbARF32 may be also involved in ethylene biosynthesis in pear fruit via the PbIAA.C3–PbARF32 interaction. The information provided new insights into the molecular regulation of ethylene biosynthesis during fruit ripening.