Mining and identification of factors influencing multi-branch plasticity in ornamental kale.

Main conclusion: Transcriptome-revealed plant hormones and nutrients are key factors influencing branching in ornamental kale. Topping treatment and exogenous hormones application revealed that auxin and SLs inhibited lateral buds outgrowth, respectively. Plant architecture is a crucial horticultural characteristic in ornamental kale as the variety of branching patterns significantly enhances the esthetic appeal of garden plants. The factors influencing multi-branch plasticity in ornamental kale are yet to be elucidated. In this study, we mined the key branching genes by comparing the transcriptomes of a single-branched inbred line 'P29' and its natural multi-branched mutant, revealing a total of 3727 differentially expressed genes (DEGs) between them. A Kyoto Encyclopedia of Genes and Genome enrichment analysis identified 41 auxin-related DEGs, 5 strigolactones (SLs)-related DEGs, 12 cytokinin-related DEGs, 3 abscisic acid-related DEGs, and 1 gibberellin-related DEG. Nutrients, such as sugar, nitrogen, and phosphorus, might also influence branching. To investigate the effects of auxin and SLs on branch outgrowth, we conducted a topping treatment (removed rosette head) and externally applied the SL analog GR24 and corresponding SL biosynthesis inhibitor TIS108 to the single-branch inbred line 'P23'. GR24 effectively inhibited lateral bud outgrowth while TIS108 promoted lateral bud initiation. This work provides a novel perspective of the multi-branch plasticity in ornamental kale and also highlights potential key elements regulating plant morphology, which could be targeted to improve the architecture of valuable plant species.