Characterization of the actin (ACT) family in Rosaceae and role of PbrACT1 in pear pollen tube growth

The actin (ACT) family genes are essential for plant growth and development. However, the evolution and function of the ACT family within the Rosaceae species, particularly in pear, remain poorly understood. Here, we identified 41 ACT genes across five Rosaceae species based on phylogenetic and structural features that can be categorized into two primary groups: subfamily I (reproductive) and II (vegetative). Evolutionary analysis suggests that purifying selection played a crucial role in the evolution of the ACT family in Rosaceae, and whole genome duplication (WGD) and dispersed duplication led to the expansion of ACT genes. The pear genome contains twelve ACT genes, which can be classified into two groups based on their phylogeny and expression patterns: reproductive (PbrACT1-5) and vegetative (PbrACT6-12), further validating the reliability of the ACT family classification in Rosaceae. Expression analysis of twelve PbrACT genes across various pear tissues indicated that five genes from subfamily I (PbrACT1-5) were predominantly expressed in pollen tubes, with PbrACT1 exhibiting the highest level of expression. Knockdown of PbrACT1 expression in pear pollen tubes significantly diminished F-actin levels, triggered F-actin depolymerization, and resulted in pollen tube growth inhibition, indicating that PbrACT1 is essential for the formation of the microfilament skeleton during pear pollen tube growth. Overall, this study offers significant insights into the evolution and function of ACT genes in Rosaceae and enhances our understanding of PbrACT in microfilament formation in pear pollen tubes.