Cell and molecular biological studies of the hypersensitive response induced in cowpea by the cowpea rust fungus

A cytological and molecular biological approach was undertaken to examine the events that occur during the very early stages of the hypersensitive response (HR) in cowpea midvein epidermal cells that are being infected by the cowpea rust fungus. The HR is one of the most-ubiquitous defense responses that plants exhibit in response to pathogen infection and has been defined as the rapid, localized cell death in association with disease resistance.; For the cytological portion of the study, stereological ultrastructural analyses of rust fungus infected and uninfected midvein epidermal cells from resistant and susceptible plants indicated that transcription and translation were up-regulated in the cells of the resistant plant while the fungus was penetrating through the plant cell wall, and prior to fungal contact with the plant plasma membrane. Conversely, in the rust-susceptible cells, there was evidence that decreases in transcription and translation occurred in the rust fungus-infected cells at this same stage of infection.; To identify genes that were up-regulated in the rust resistant cowpea cells during this very early stage of the penetration process, cytoplasm was extracted from individual epidermal cells of rust fungus-inoculated and uninoculated plants that were either resistant or susceptible to the fungus. RNA was isolated from each of the extracted cell types and amplified in a non-gene-specific manner in order to generate a 3′ EST library for each of the four cell types. Differential screening of the library generated from the infected-resistant cells resulted in the identification of three overall groups of genes. These were genes that were up-regulated in both the infected-resistant and -susceptible cells, those that appeared to be suppressed in the infected-susceptible plants and those that were up-regulated only in the infected-resistant cells. Genes in the latter situation differed from those reported previously for studies of the HR that involved sample tissue including both living cells and those advanced in the death process.