Mycelium homogenates from a virulent strain of Phytophthora capsici promote a defence-related response in cell suspensions from Capsicum chinense

Abstract

We analysed changes in the transcript population produced in habanero pepper (Capsicum chinense) cell suspensions by the addition of whole mycelium homogenates from a pathogenic isolate of Phytophthora capsici, to identify plant cellular processes modified by the oomycete effectors. The elicitation produced several defence-like cellular responses: alkalinisation of the medium, a two-step oxidative burst, induction of β-1,3-glucanases, and activation of mitogen-activated protein kinases. The elicitation modified the accumulation of transcripts representative of diverse metabolic pathways, including ethylene biosynthetic enzymes, MAP kinases and defence-related products, like PR proteins, but did not affect the expression of C. chinense NPR1 and WRKY orthologue genes, which are important modulators of plant defence responses. Interestingly, apart from some defence-related genes, inoculation of six-leaf-stage habanero pepper plantlets with the pathogenic isolate revealed few systemic modifications in the transcript patterns. All plantlets ultimately died, even though the in planta inoculation induced the strong accumulation of two MAPK transcripts. As few resistance-related genes were expressed in susceptible habanero pepper plantlets that died, either the extent or the timing of the defence response could be insufficient to establish a proper response against Phytophthora blight.