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

Abstract

Fruit softening is an important characteristic of peach fruit ripening. The auxin receptor TIR1 (Transport Inhibitor Response 1) plays an important role in plant growth and fruit maturation. Still, little research has been conducted on the relation of TIR1 to the softening of peach fruits. In this study, the hardness of isolated peach fruits was reduced under exogenous NAA treatment at low concentrations. At the same time, the low concentration of NAA treatment reduced the transcription level of PpPG and Ppβ-GAL genes related to cell wall softening and PpACS1 genes related to ethylene synthesis. The transient overexpression of the PpTIR1 gene in peach fruit blocks caused significant down-regulation of the expression of early auxin-responsive genes, ethylene synthesis, and cell wall metabolic genes related to fruit firmness. Through yeast two-hybrid technology, bimolecular fluorescence complementary technology, and a firefly luciferase complementation imaging assay, we were able to unveil an interaction between PpTIR1 and PpIAA1/3/5/9/27 proteins. Furthermore, it was determined that the interaction depended on auxin and its type and concentration. These results show that the PpTIR1-Aux/IAA module has a possible regulatory effect on fruit ripening and softening.