Transcriptome reveals endogenous hormone signal transduction and cell wall remodeling mediating compatibility in apple-pear intergeneric distant hybridization.

Distant hybridization is critical for fruit tree germplasm innovation yet difficult to achieve in woody fruit trees. Successful distant hybridization between apple and pear is rare among fruit trees, but the molecular mechanism of their compatibility remains unclear. Revealing this biological process is vital for the innovation of fruit tree cultivation. This study performed distant hybridization experiments using cultivated apple as female parents and multiple pear cultivars as male parents, and obtained compatible hybrids from the cross of 'YYH' apple × 'YH' pear. To investigate the underlying mechanisms, transcriptome sequencing was performed on unpollinated apple styles as controls, and gene expression profiles of styles were constructed following both intraspecific apple pollination and apple-pear distant hybridization pollination. The results indicated that both pollination treatments significantly activated the ethylene, brassinosteroid, and jasmonic acid signaling pathways. Notably, jasmonic acid played a central role in precise feedback regulation, with the substantial upregulation of the negative regulatory factor JAZ potentially serving as a critical mechanism for balancing pollen tube growth and immune defense. Meanwhile, genes associated with cellulose and pectin were upregulated, thereby promoting the remodeling of the style cell wall to facilitate the penetration and elongation of the pollen tube. The response patterns were highly consistent between the two pollination combinations, indicating that the distant hybridization of apples and pears shares similar regulatory mechanism with apple intraspecific pollination. This study provides a theoretical basis and data support for revealing the compatibility mechanism of distant hybridization in fruit trees and breaking through reproductive barriers.