Interaction of barley powdery mildew effector candidate CSEP0055 with the defence protein PR17c

Abstract

A large number of effector candidates have been identified recently in powdery mildew fungi. However, their roles and how they perform their functions remain unresolved. In this study, we made use of host-induced gene silencing and confirmed that the secreted barley powdery mildew effector candidate, CSEP0055, contributes to the aggressiveness of the fungus. This result suggests that CSEP0055 is involved in the suppression of plant defence. A yeast two-hybrid screen indicated that CSEP0055 interacts with members of the barley pathogenesis-related protein families, PR1 and PR17. Interaction with PR17c was confirmed by bimolecular fluorescence complementation analyses. Down-regulation and over-expression of PR17c in epidermal cells of barley confirmed that this protein is important for penetration resistance against the powdery mildew fungus. In line with this, PR17c was found to be apoplastic, localizing to the papillae formed in response to this fungus. The CSEP0055 transcript did not start to accumulate until 24 h after inoculation. This suggests that this gene is expressed too late to influence primary penetration events, but rather sustains the fungus at sites of secondary penetration, where PR17c appears to be able to accumulate.

Host-Induced Gene Silencing in Barley Powdery Mildew Reveals a Class of Ribonuclease-Like Effectors

“…The CSEP superfamily includes many of the genes and proteins previously identified as specifically expressed in haustoria ) and in infected epidermis (Bindschedler et al 2009(Bindschedler et al , 2011. One member of this superfamily, CSEP0055, has recently been shown to reduce HI when silenced by HIGS and interacts with barley pathogenesis-related protein PR17c and is, therefore, an experimentally validated effector (Zhang et al 2012). Apart from this protein, however, the majority of candidate effectors of B. graminis have yet to be characterized.…”

The wheat powdery mildew genome shows the unique evolution of an obligate biotroph

“…This process allows selection for either effector changes or loss. It is postulated that the specific makeup of effectors determines the virulence spectrum of a particular mildew strain 7,[11][12][13] (Supplementary Note). Here we wanted to study genetic diversity between and within powdery mildew formae speciales and explore the impact of the introduction of the new host (bread wheat) on B. graminis f.sp.…”

Mosaic genome structure of the barley powdery mildew pathogen and conservation of transcriptional programs in divergent hosts

“…Therefore, an active secretion mechanism has been proposed that exports these CSEPs from the haustorium (22). Furthermore, although detailed biological roles of most CSEPs have not been documented, host-induced gene silencing (23) of some CSEPs suggested their role in host-defense suppression (24,25). Notably, the CSEP repertoire of Bgh is strikingly different from those of the distantly related Golovinomyces orontii and Erysiphe pisi powdery mildews, suggesting specific adaptations to their respective host plants (15).…”