Abstract
Receptor‐like
kinases (RLKs) are important components of plant innate immunity. Although
recent studies have revealed that the RLK SUPPRESSOR OF BIR1‐1 (SOBIR1)
can interact with multiple receptor‐like proteins (RLPs)
and is required for resistance against fungal pathogens, how the signal is
transduced and triggers immune responses remains enigmatic. In this study, we
identified a defense‐related RLK from Gossypium barbadense
(designated GbSOBIR1) and investigated its functional mechanism. Expression of
the GbSOBIR1 gene is ubiquitous in cotton plants and is induced by Verticillium
dahliae inoculation. Knock‐down of GbSOBIR1 by virus‐induced
gene silencing resulted in attenuated resistance of cotton plants to V.
dahliae, while heterologous overexpression of GbSOBIR1 in Arabidopsis improves
resistance. We also found that the kinase region of GbSOBIR1 interacts with a
basic helix‐loop‐helix (bHLH)
transcription factor identified as GbbHLH171 in a yeast‐two‐hybrid
screen. GbbHLH171 could interact with and be phosphorylated by GbSOBIR1 in
vitro and in vivo and contributes positively to the resistance of cotton
against V. dahliae. Furthermore, we found that this phosphorylation is
essential to the transcriptional activity and functional role of GbbHLH171. We
also show by spectrometric analysis and Site‐directed mutagenesis
that Ser413 is the GbSOBIR1‐mediated phosphorylation site of
GbbHLH171. These results demonstrate that GbSOBIR1 interacts with GbbHLH171 and
plays a critical role in cotton resistance to V. dahliae.