Actin dynamic polymerization is required for the expression of nonhost resistance in pepper against Blumeria graminis f. sp. tritici

Abstract

The roles of the actin cytoskeleton in nonhost resistance of pepper inoculated with the non-pathogen Blumeria graminis f. sp. tritici (Bgt) was studied at molecular and histological levels in a detailed time-course experiment. The expression patterns of three actin remodeling associated genes, Profilin, Actin depolymerizing factor (ADF) and Rho, were detected in inoculated pepper leaves by qRT-PCR. The actin polymerization inhibitor latrunculin B was then applied to demonstrate the effects of actin depolymerization on different defense reactions. The results showed that the expression of Rho and Profilin was up-regulated significantly after the inoculation of Bgt. After the treatment with latrunculin B, the frequency of whole-cell H2O2 and papilla accumulation was significantly reduced, and the produce of H2O2 in infected cells and the deposition of papilla at fungal penetration sites were also suppressed. In addition, hypersensitive-response-like cell death (showing weak trypan blue staining and without visible epidermal cell deformation) was stimulated in the early stage of the incubation period and thereafter normal hypersensitive-response was suppressed. Moreover, the percentage of haustorial formation also had a dramatic increase in the early stage of the incubation period, and up to 53% germinating Bgt conidia were able to successfully penetrate the epidermis to form central haustorial bodies. These results strongly indicate that actin cytoskeleton is closely related to the nonhost resistance in pepper against Bgt, and actin polymerization is necessary for the expression of pepper nonhost resistance.