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, and it is regulated by multiple plant hormones including strigolactones (SLs), auxin, and cytokinin; 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 results for gene expression that correlated with either bud outgrowth or bud growth suppression in petunia from a previous study, 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/DEHYDROGENASE3/5 double-mutant (ckx3 ckx5) showed significant reductions in rosette branching and altered flowering time relative to the wild type. Transcriptome comparisons between these mutants and the wild type suggested that up-regulation 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 provide new insights into the regulation and connections between SL and other hormones and developmental processes.