The Arabidopsis F-box protein FBS associated with the helix-loop-helix transcription factor FAMA involved in stomatal immunity.

Stomatal pores serve as primary entry points for pathogen invasion. Stomatal closure is a crucial strategy that plants employ to counter pathogen attack. Here, we report that F-BOX STRESS-INDUCED (FBS) is essential for modulating stomatal closure, thereby enhancing resistance to bacteria in Arabidopsis thaliana. The fbs2-1 fbs3-1 fbs4-2 triple mutant displayed increased susceptibility to Pseudomonas syringae pv. tomato (PstDC3000) due to impaired stomatal closure. Additionally, FBS4 interacts with and degrades the basic helix-loop-helix (bHLH) transcription factor FAMA. Both the fama-1 single mutant plants and the fama-1 fbs2-1 fbs3-1 fbs4-2 quadruple mutant plants exhibited resistance to PstDC3000 inoculation. Furthermore, the expression levels of abscisic acid (ABA)-responsive genes RD29A, RD29B, ABI2, and CIPK25 were altered in the fbs2-1 fbs3-1 fbs4-2 and fama-1 mutant plants. Collectively, our data demonstrate that FBS, in association with FAMA, plays an important role in pathogen invasion by influencing ABA signaling-related stomatal closure.