SAUR15 interaction with BRI1 activates plasma membrane H+-ATPase to promote organ development of Arabidopsis

• Published in: Plant physiology (Bethesda) Vol. 189; no. 4; pp. 2454 - 2466
• Main Authors: Li, Mengzhan, Liu, Chunli, Hepworth, Shelley R, Ma, Chaofan, Li, Hong, Li, Jia, Wang, Suo-Min, Yin, Hongju
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01-08-2022
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1093/plphys/kiac194

Brassinosteroids (BRs) are an important group of plant steroid hormones that regulate growth and development. Several members of the SMALL AUXIN UP RNA (SAUR) family have roles in BR-regulated hypocotyl elongation and root growth. However, the mechanisms are unclear. Here, we show in Arabidopsis (Arabidopsis thaliana) that SAUR15 interacts with cell surface receptor-like kinase BRASSINOSTEROID-INSENSITIVE 1 (BRI1) in BR-treated plants, resulting in enhanced BRI1 phosphorylation status and recruitment of the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1). Genetic and phenotypic assays indicated that the SAUR15 effect on BRI1 can be uncoupled from BRASSINOSTEROID INSENSITIVE 2 (BIN2) activity. Instead, we show that SAUR15 promotes BRI1 direct activation of plasma membrane H+-ATPase (PM H+-ATPase) via phosphorylation. Consequently, SAUR15-BRI1-PM H+-ATPase acts as a direct, PM-based mode of BR signaling that drives cell expansion to promote the growth and development of various organs. These data define an alternate mode of BR signaling in plants.