Objective Significant differences in fruit texture exist among different hawthorn varieties, yet the molecular basis underlying this variation remains unclear. This study aims to identify members of the polygalacturonase (PG) gene family, a key factor in fruit softening, through a genome-wide analysis using hawthorn varieties with contrasting fruit texture, to investigate their expression specificity during fruit softening and varietal texture differentiation, and to screen for key PG genes regulating fruit firmness. The findings will provide a theoretical foundation for deciphering the regulatory mechanisms of hawthorn fruit texture and offer candidate gene resources for future molecular design breeding to improve hawthorn fruit quality.

Method Based on hawthorn genomic data, PG gene family members were identified, and their physicochemical properties, subcellular localization, phylogeny, gene structure, conserved Motifs, cis-acting elements in promoters, and transcription factor binding sites were analyzed. The chromosomal distribution, gene duplication types, selective pressure, and interspecies collinearity were also resolved. The fruit firmness and pectin content of ‘Jinruyi’ and ‘Yubeihong’ during fruit development were measured. CpPG expression patterns were analyzed by qRT-PCR, and correlation analysis between gene expression levels and phenotypic data was performed.

Result (1) In the hawthorn genome, a total of 68 CpPG genes were identified. Their physicochemical properties varied considerably, and approximately 44% of the CpPG proteins were predicted to be localized in the nucleus. (2) Phylogenetic analysis divided them into six subfamilies. The gene structure of members within each subfamily was relatively conserved, and all CpPG contained the Glyco_hydro_28 catalytic domain and five conserved Motifs. (3)Analysis of cis-acting elements in the promoters revealed that the promoter regions of CpPG are enriched in hormone-responsive and low-temperature-responsive elements. (4) Gene duplication analysis indicated that whole-genome duplication and dispersed duplication are the main modes of CpPG family expansion, and purifying selection is the major driving force for its evolutionary conservation. (5) In the two varieties with contrasting fruit firmness, ‘Jinruyi’ and ‘Yubeihong’, fruit firmness gradually decreased during fruit softening. Total pectin content showed a trend of first increasing and then decreasing, while water-soluble pectin content continuously increased with ripening. (6) qRT-PCR results showed that CpPG4 was specifically highly expressed in the G1 group during the late stages of fruit development, and its expression level in ‘Jinruyi’ was extremely significantly higher than that in ‘Yubeihong’. (7) Only the expression level of CpPG4 was extremely significantly negatively correlated with fruit firmness and extremely significantly positively correlated with water-soluble pectin content, indicating that CpPG4 is a key gene regulating fruit softening and varietal texture differentiation in hawthorn.

Conclusion A total of 68 CpPG genes were identified in the hawthorn genome. Their promoters are generally enriched in low-temperature-and hormone-responsive elements. The family expansion mainly relies on dispersed duplication and whole-genome duplication, and purifying selection maintains its evolutionary conservation. CpPG4 drives fruit softening by promoting pectin solubilization, and its differential expression between varieties is a key molecular basis for fruit texture differentiation. This study provides a theoretical basis for deciphering the molecular mechanism of fruit texture formation in hawthorn and offers key gene resources for improving fruit firmness through molecular breeding .