Genome-wide identification and expression analysis of the FWL genes family in kiwifruit identifies AcFWL13 as a candidate associated with early fruit development

Fruit size is an important determinant of crop yield, quality and consumer preference. In tomato, fw2.2 (single fruit weight 2.2) negatively regulates fruit size by controlling cell division and expansion in carpel ovary during development. At present, its homologous genes have been identified in a variety of plants, but the comprehensive study of the FWL gene family in kiwifruit is still limited. In this study, in order to explore the key regulatory factors of kiwifruit ( Actinidia chinensis ‘Hongyang’) fruit size development, we systematically identified and analyzed the expression of FWL gene family in kiwifruit. A total of 16 AcFWL genes were identified, named AcFWL1 - AcFWL16 , which were unevenly distributed on 11 chromosomes, with evidence of purification selection. Phylogenetic analysis divided 78 FWL proteins into five different subfamilies. Promoter analysis identified Cis-acting elements associated with hormone, light, fruit growth and developmental responses, suggesting possible regulatory diversity among AcFWL genes. On this basis, combined with multi-dimensional screening such as potential protein–protein interaction (PPI) network, and weighted gene co-expression network analysis (WGCNA), AcFWL13 showed unique regulatory potential. Its Hub gene ranked in the top 400 and ranked second among family members. Crucially, transcriptome and RT-qPCR results showed that AcFWL13 expression peaked before 15 DAFB (the early fruit-development stage) and then continued to decrease during 15–75 DAFB expansion. In summary, we speculate that AcFWL13 may be a potential key candidate gene involved in kiwifruit fruit size development and may play a regulatory role as an early developmental signaling node. These results suggest that AcFWL gene may play an important role in fruit development. Among them, AcFWL13 was locked as the primary candidate gene involved in fruit development, which provided molecular targets for subsequent functional verification, allele diversity mining and fruit trait association analysis. This will help us better understand the regulation mechanism of kiwifruit fruit size and lay a preliminary foundation for molecular marker-assisted breeding in the future.