ENSNARING MICROBES - THE COMPONENTS OF PLANT-DISEASE RESISTANCE

Plants activate an array of co-ordinated defence responses to restrict microbial attack. Timely perception of foreign molecules appears to b e critical for the success of these defences. However, the nature of t he molecular events required for resistance is largely unknown. Recent isolation of disease resistance (R) genes, has revealed that R gene p roducts have several features in common. This finding suggests that pl ants have evolved several common or similar signal transduction pathwa ys to activate resistance to a range of unrelated microbes. R gene iso lation and the genetic identification of other loci required for R fun ction permits analysis of the structure and evolution of microbe-perce ption mechanisms. Numerous types of activated defence responses are re cognized. A requirement for salicylic acid in resistance has been esta blished in some systems. Roles for other events, like reactive oxygen species and the hypersensitive (host cell death) response, remain enig matic. A thorough understanding of the components leading to pathogen recognition and the expression of resistance should permit thr design of novel strategies to engineer broad-spectrum and durable plant disea se control.