Morphological observation and transcriptome profiling of axillary buds with different identities in response to...

In strawberry plants, axillary buds can develop into short branches (branch crowns) that form inflorescences or long branches (runners) that produce daughter plants for vegetative propagation. Gibberellin (GA) is the key hormone promoting runner outgrowth, but the underlying mechanisms remain unclear. The woodland strawberry (Fragaria vesca) variety 'Hawaii 4' (H4) develops both branch crowns and runners depending on the internal or external factors, whereas 'Yellow Wonder' (YW) exclusively produces branch crowns. This divergence in axillary bud fate is determined by a mutation in the GA biosynthesis gene FveGA20ox4. In this study, we found that exogenous GA₃ treatment of YW resulted in runner production, whereas application of the GA biosynthesis inhibitor paclobutrazol (PBZ) could prevent the runners and increase branch crown production in H4. We conducted a detailed morphological characterization of early axillary bud development, categorizing it into four distinct stages. To identify regulatory genes in axillary bud fate determination and early development, the axillary buds of YW-Mock, YW-GA₃, H4-Mock and H4-PBZ from stage 1 to stage 4 were pooled and subjected to transcriptome analysis. Pairwise comparisons revealed differentially expressed genes (DEGs), including transcription factors, hormones and cell wall-related genes. Notably, the transcription factor encoding genes FveNAC43 and FveMYB46, along with the cellulose synthesis genes FveCESA7 and FveCESA8, were up-regulated in H4-mock and YW-GA₃ axillary buds, which adopt a runner identity. Our results provide new insights into the molecular mechanisms of runner development in strawberry. The identified DEGs may serve as candidate targets for optimizing axillary bud production in strawberry breeding programs.