Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/24/2003
Publication Date: 12/1/2003
Citation: Kruger, W.M., Szabo, L.J., Zeyen, R.J. 2003. Temporal accumulation of barley defense gene transcripts induced by Blumeria graminis f.sp. hordei in isolines containing Mla1, Mla12, Mlp, Mlg, and Mla5 resistance genes. Physiological and Molecular Plant Pathology. 63:167-178. Interpretive Summary: Plants are able to mount different types of defensive response when they are attacked by plant pathogens. There is a general defense response, which is activated by all pathogens and a second response which is able to recognized specific pathogens and often races of a pathogen. Experiments were carried out to study the potential interaction between these two defense response systems using barely and the powdery mildew pathogen. Gen expression for three general defense response genes were monitored in different barley lines, each with a different specific resistance gene. The results indicate that the two types of defense mechanisms are independent of each other. These results provide basic information on how the defense systems in plants work and is essential to developing new and novel types of control for plant disease. These results will be useful to plant pathologists and plant breeders as they develop new strategies to control plant diseases and to those using biotechnology approaches to enhance disease resistance.
Technical Abstract: Plants have two basic types of defense mechanisms against pathogens, disease resistance genes which are pathogen-specific and often race- specific, and disease response genes which are more general. In order to study the potential interaction between these two systems mRNA levels of three general response genes (chitinase II, phenylalanine ammonia lyase [PAL] and peroxidase) were measured in seven different barley isolines fro 0 to 72 hours after inoculation (hai) with the mildew pathogen Blumeria graminis f.s;. hordei. These near-isogenic barley Pallas lines contained fast-acting (mlo5, Mla1, and Mlg), intermediate-acting (Mla12) and slow- acting (Mlk and Mlp) powdery mildew resistance genes, as well as a susceptible line (Pallas). During the first 24 hai the resistant and susceptible isolines had a similar biphasic, temporal patterns of mRNA transcript accumulation for the three defense response genes. At 36 to 72 hai the transcript accumulation levels in each barley isoline generally corresponded with the extent of powdery mildew hypal growth. A primary exception to this was the susceptible barley line, in which extensive hypal growth occurred, but the levels of transcript accumulation declined after 24, similar to what was observed in the iso-lines containing fast-acting resistance genes suggesting that there may be suppression of the general disease response genes.