Effects of exogenous GA, IAA, ABA and ethylene on pear (Pyrus pyrifolia) fruit during different development stages

Phytohormones play crucial roles in fruit development and ripening. However, it is unclear the role of phytohormones in pear fruit quality, such as transverse and longitudinal diameters, fruit weight, soluble solid, titratable acid. In this study, four phytohormone treatments which included gibberellin (GA), Indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ETH) were performed to treat pear (Pyrus pyrifolia) fruit at different stages, including 30, 45, 60, 75 and 90 days after flower blooming (DAFB). As a result, exogenous GA treatment could promote fruit enlargement, reduce fruit firmness and inhibit the accumulation of titratable acid in ripening fruit (110DAFB). Both exogenous IAA and ABA treatments could also promote fruit enlargement. Moreover, both exogenous ABA and ETH treatment could promote the accumulation of soluble solids in 110DAFB, indicating the involvement of ABA and ETH in fruit ripening. Quantitative real-time PCR (qRT-PCR) analysis suggested that PbZEP1, PbNCED.B, PbSDR4 and PbAO3 are the crucial genes for ABA biosynthesis, PbACS1b and PbACO1 are crucial genes for ethylene biosynthesis in pear fruit. EMSA and Dual-luciferase assay suggested that PbABF.B and PbABF.C.2 directly bind to the promoter of PbACS1b, while PbABF.E.1 and PbABF.E.2 directly bind to the promoter of PbACO1 to enhance their activities. These results indicate that the four ABF proteins may be involved in ethylene biosynthesis during fruit ripening. Our study establishes the roles of GA, IAA, ABA and ethylene in pear fruit and finds the crosstalk between ABA and ETH during fruit ripening.