New paper from Hückelhoven lab.
A barley SKP1-like protein controls abundance of the susceptibility factor RACB and influences the interaction of barley with the barley powdery mildew fungus.
Tina Reiner, Caroline Hoefle and Ralph Hückelhoven
In an increasing number of plant–microbe interactions, it has become evident that the abundance of immunity-related proteins is controlled by the ubiquitin–26S proteasome system. In the interaction of barley with the biotrophic barley powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh), the RAC/ROP [RAT SARCOMA-related C3 botulinum toxin substrate/RATSARCOMA HOMOLOGUE (RHO) of plants] guanosinetriphosphatase (GTPase) HvRACB supports the fungus in a com-patible interaction. By contrast, barley HvRBK1, a ROP-bindingreceptor-like cytoplasmic kinase that interacts with and can be activated by constitutively activated HvRACB, limits fungal infec-tion success. We have identified a barley type II S-phase kinase1-associated (SKP1)-like protein (HvSKP1-like) as a molecularinteractor of HvRBK1. SKP1 proteins are subunits of the SKP1-cullin 1-F-box (SCF)–E3 ubiquitin ligase complex that acts in the specific recognition and ubiquitination of protein substrates forsubsequent proteasomal degradation. Transient induced gene silencing of either HvSKP1-like or HvRBK1 increased proteinabundance of constitutively activated HvRACB in barley epider-mal cells, whereas abundance of dominant negative RACB only weakly increased. In addition, silencing of HvSKP1-like enhancedthe susceptibility of barley to haustorium establishment by Bgh. In summary, our results suggest that HvSKP1-like, together with HvRBK1, controls the abundance of HvRACB and, at the sametime, modulates the outcome of the barley–Bgh interaction. A possible feedback mechanism from RAC/ROP-activated HvRBK1on the susceptibility factor HvRACB is discussed.
