Mutation of SCARECROW-LIKE28 or CYTOKININ OXIDASE3/5 suppresses rosette branching in Arabidopsis

Shoot branching is an important trait that influences plant architecture and crop productivity. It is triggered by the perception of developmental and environmental cues and controlled by a complex and interconnected regulatory network. Multiple plant hormones, including strigolactones (SLs), auxin and cytokinin (CK) regulate branching; however, the interplay between them has yet to be fully elucidated. In this study, branching regulators were identified through a series of transcriptomic, functional and genetic studies. Based on gene expression that was correlated with either bud growth suppression or bud outgrowth in petunia from our previous work, candidates for branching regulation were selected, and their functions in modulating branching were studied using Arabidopsis mutant lines. The SCARECROW-LIKE28 mutant (scl28) and CYTOKININ OXIDASE/DEHYDROGENASE double mutant (ckx3 ckx5) showed significant reduction in rosette branching and altered flowering time relative to wild type (WT) Arabidopsis. Transcriptome comparison between these mutants and WT suggested upregulation of SL biosynthesis genes in the mutants might contribute to the suppression of rosette branching. This was supported by genetic data indicating that SCL28 and CKX3/5 regulate rosette branching via the SL signalling pathway but regulate flowering independently. These findings add new knowledge to the regulation and connection between SL and other hormones and developmental processes.