RNA interference knockdown of the brassinosteroid receptor BRI1 in potato (Solanum tuberosum L.) reveals novel functions for brassinosteroid signaling in controlling tuberization

• Three genes, StBRI1, StBRL1 , and StBRL2 , were identified in potato genome. • StBRI1 is an active LRR-RLK protein and is highly expressed in tubers. • Overexpression of StBRI1 in bri1-5 plants partially restores BR signaling intensity. • Knockdown of StBRI1 in potato attenuates BR signaling and compromises tuberization. Brassinosteroids (BRs) play critical functions in a broad range of plant growth and development processes, and components of the BR signaling pathway have been characterized, including the BR receptor, BRASSINOSTEROIDS INSENSITIVE 1 (BRI1). Studies in several crop species have shown that altering the expression of BR receptor genes can result in improved growth, yield and stress-resistance; However, little is known about the role of BR receptors in potato ( Solanum tuberosum ) tuber development. Here, three potato genes, StBRI1, StBRI1-like 1 ( StBRL1 ), and StBRL2 , encoding potential BR receptors, were identified. Expression analysis indicated that StBRI1 was ubiquitously and highly expressed in various potato plant tissues, but especially in tubers. Conserved domain, subcellular localization, and kinase activity analyses revealed that StBRI1 encodes an active leucine-rich repeat (LRR) receptor-like kinase (RLK) protein localized in the plasma membrane. Overexpression of StBRI1 in the Arabidopsis thaliana bri1-5 mutant resulted in partial rescue of the bri1-5 dwarf phenotype and increased BR signaling. RNA interference (RNAi) using partial fragment corresponding to the extracellular region of StBRI1 knocked down the transcription of all three homologs. Transgenic potato plants in which StBRI1 expression was reduced using RNAi exhibited a dwarf phenotype, decreased BR signaling, and reduced tuberization. Regulation of tuberization by StBRI1 was further verified by silencing StBRI1 expression specifically in tubers. Taken together, these results demonstrated that StBRI1 is a functional potato BR receptor and reveals a novel function for brassinosteroid signaling in controlling tuberization.