A conserved brassinosteroid-mediated BES1-CERP-EXPA3 signaling cascade controls plant cell elongation

Continuous plant growth is achieved by cell division and cell elongation. Brassinosteroids control cell elon-gation and differentiation throughout plant life. However, signaling cascades underlying BR-mediated cell elongation are unknown. In this study, we introduce cotton fiber, one of the most representative single-celled tissues, to decipher cell-specific BR signaling. We find that gain of function of GhBES1, a key transcriptional activator in BR signaling, enhances fiber elongation. The chromatin immunoprecipitation sequencing anal-ysis identifies a cell-elongation-related protein, GhCERP, whose transcription is directly activated by GhBES1. GhCERP, a downstream target of GhBES1, transmits the GhBES1-mediated BR signaling to its target gene, GhEXPA3-1. Ultimately, GhEXPA3-1 promotes fiber cell elongation. In addition, inter-species functional analysis of the BR-mediated BES1-CERP-EXPA3 signaling cascade also promotes Arabidopsis root and hypocotyl growth. We propose that the BES1-CERP-EXPA3 module may be a broad-spectrum pathway that is universally exploited by diverse plant species to regulate BR-promoted cell elongation.

Automated summary

Continuous plant growth relies on cell division and elongation, which is regulated by brassinosteroids (BR). In this study, the researchers used cotton fiber to investigate cell-specific BR signaling and found that the transcriptional activator GhBES1 promotes fiber elongation by activating GhCERP, a protein related to cell elongation. GhCERP then transmits the BR signal to its target gene GhEXPA3-1, which ultimately promotes fiber cell elongation. Furthermore, the BR-mediated BES1-CERP-EXPA3 signaling cascade also promotes root and hypocotyl growth in Arabidopsis, indicating its broad significance in regulating BR-promoted cell elongation.