An Overview of Active Disease Defense in Plants

Abstract

The active hypersensitive defense response (HR) of plants may be triggered by general elicitors, produced by an entire pathogen species or genus, or by specific elicitors which function only in plant cultivars carrying complementary or cognate disease resistance genes. Specific elicitors arise from the activity of avirulence genes in the pathogen which complement matching plant disease resistance genes. Following elicitortreatment of plant tissue, intracellular and systemic signalling mechanisms occur, the details of which are not yet well understood. However, these signals cause relatively rapid derepression of batteries of defense response genes which appear to be involved with the actual process of restricting pathogen development. A major current research area involves the attempted cloning and characterization of disease resistance genes, which are thought to encode specific receptors for pathogen-produced elicitors. In addition, efforts are being made to understand the signal transduction pathways and trans-acting factors which account for defense response gene activation. Recent experiments have also shown that transgenic plants over-expressing certain defense response and other genes may be resistant to pathogen attack.