CsBRC1 inhibits axillary bud outgrowth by repressing auxin efflux carriers CsPIN1b and CsPIN3 and in response to shade in cucumber

Shoot branching is an important agronomic trait that directly determines plant architecture and affects crop productivity. To promote crop yield and quality, axillary branches need to be manually removed during cucumber production for fresh market and thus are undesirable. Auxin is well known as the primary signal imposing for apical dominance and acts as a repressor for branching outside of the lateral buds. The TEOSINTE BRANCHED1/CYCLOIDEA /PCF (TCP) family gene BRANCHED1 (BRC1) has been shown to be the central integrator for multiple environmental and developmental factors that functions locally to inhibit shoot branching. However, no direct link has been reported between auxin and BRC1. Here, we find that cucumber BRANCHED1 (CsBRC1) is expressed in the axillary buds and displays higher expression level in cultivated cucumber than its wild ancestor. Knockdown of CsBRC1 by RNAi leads to increased bud outgrowth and reduced auxin accumulation in buds. We further show that CsBRC1 directly binds to two auxin efflux carriers PIN-FORMED (CsPIN1b and CsPIN3) and negatively regulates their expression. Ectopic expression of CsPIN1b or CsPIN3 driven by CsBRC1 promoter results in increased shoot branching. Moreover, shade induces the expression of CsBRC1 in cultivated cucumber, but not in wild ancestor, which may be partly due to the addition of two light response elements in the CsBRC1 promoter of cultivated cucumber. Therefore, our data suggest the formation of a regulatory pathway of shade-CsBRC1-auxin transport in suppressing lateral bud outgrowth during cucumber domestication. Sequencing data of axillary buds in wild-type and CsBRC1-RNAi lines cucumber.