Genome-wide identification of the C2-domain abscisic acid-related (CAR) protein family in Rosaceae and functional characterization of PbrCAR1 in pear pollen tube growth.

This study identified a PbrCAR1 gene in pear, which promotes pollen tube growth by mediating vesicle transport, and Ca treatment enhances PbrCAR1 expression and promotes its plasma membrane accumulation. The C2-domain abscisic acid-related (CAR) proteins bind to diverse signaling protein complexes and play essential roles in numerous biological processes, including blue light tropism, gravitropism, iron nutrition, and responses to biotic and abiotic stresses. However, the functions of CAR gene family members in pear pollen development within the Rosaceae family remain inadequately explored. In this study, we identified a total of 33 CAR genes across four Rosaceae species. Phylogenetic and structural analyses classified these genes into three distinct subfamilies (I to III). Evolutionary analyses indicated that purifying selection significantly influenced the evolution of the Rosaceae CAR gene family, while whole-genome duplication and tandem duplication contributed substantially to its expansion. Transcriptomic data combined with quantitative real-time PCR (qRT-PCR) analysis revealed tissue-specific expression patterns of PbrCAR genes, with PbrCAR1 showing high expression during pollen development and mainly localizing in the cytoplasm. Exogenous calcium ion (Ca⁺) treatment was shown to enhance the expression of PbrCAR1 and promote its accumulation at the plasma membrane. Moreover, knocking down PbrCAR1 in pear pollen tubes significantly inhibited vesicle trafficking at the pollen tube tip, thereby suppressing pollen tube growth. These findings indicate that PbrCAR1 regulates pear pollen tube growth by mediating vesicle transport and provide valuable insights along with a theoretical foundation for studying the evolution, expression patterns, and functions of the CAR gene family in plants.