Genome-wide identification of the AcBAM family in kiwifruit (Actinidia chinensis cv. Hongyang) and the expression profiling analysis of AcBAMs reveal their role in starch metabolism

After analyzing a high-quality 'Hongyang' genome, we identified 17 AcBAMs. Comprehensive bioinformatics were performed to elucidate the properties and evolutionary relationships of these genes. Our analysis revealed that most AcBAMs retained conserved active sites (e.g., Glu186 and Glu380) and exhibited similar structural properties. Phylogenetic and collinearity analyses grouped the genes into three main clusters, with segmental and tandem duplications contributing to their expansion. Expression profiling showed that AcBAM5 and AcBAM13 were most highly expressed during postharvest storage and were strongly induced by ABA signal. Silencing these genes led to a significant increase in starch content, suggesting their key role in starch degradation. Promoter analysis identified cis-elements related to ABA signal and cold response in the AcBAM family, and the expression of AcBAM genes was influenced by ABA and low-temperature treatments, with specific genes showing significant responsiveness.Background Kiwifruit (Actinidia chinensis cv. Hongyang) is a perennial woody fruit tree highly valued for its rich nutritional profile and high vitamin C content. The postharvest ripening process, characterized by starch degradation into soluble sugars, significantly influences the fruit's flavor and texture. β-amylase (BAM) has been proven to be one of the key enzymes catalyzing starch degradation, but which BAM genes are involved and how to participate in this process in kiwifruit still need to be clarified.Conclusion In the study, we identified a total of 17 AcBAM genes. The expansion of AcBAMs in kiwifruit was mainly due to segmental duplication events, and some of their catalytic residues were mutated, potentially leading to a loss of biological activity. The expression patterns of AcBAMs, along with VIGS data, suggest that AcBAM5 and AcBAM13 respond to ABA signals and promote starch degradation. Our findings provide valuable insights into the regulatory mechanisms of BAM genes in kiwifruit and highlight their importance in starch metabolism and fruit ripening.