Gene transcript profiling of single barley epidermal cells attacked by powdery mildew (abstract only)

Resistance or susceptibility in barley to powdery mildew is determined at the single cell level. The fungus attempt to penetrate the plant cell wall and the attacked barley epidermal cell tries to prevent this by reinforcing its cell wall. However, this defence is only partially efficient and a number of fungal penetration attempts will succeed, leading to a mixture of infected and uninfected epidermal cells on the leaf. This makes it impossible to relate powdery mildew induced gene expression to resistance or susceptibility. Using glass micro-capillaries and micromanipulation we extracted contents from single barley epidermal cells. Three situations were considered: A) the barley cell resisted fungal penetration, B) the barley cell was infected and C) the barley cell was uninfected. The content of mRNA in the micro-extracts was purified and cDNA libraries were produced. Verification of the integrity of these libraries was done by gene specific PCR of selected genes and dot-blot hybridisation. Powdery mildew attack induces expression of a series of pathogenesis related (PR) genes in barley. Using dot-blot technique the expression of these genes was examined in the sampled cells. Notably, the PR genes were only induced in the cells that resisted powdery mildew penetration, whereas this activation was not observed in cells that were successfully invaded by the fungus. This indicates that the PR genes are involved in the processes leading to prevention of fungal penetration and that the fungus is able to prevent induction or suppress expression of the PR genes when barley cells are successfully infected.