PLANT DEFENSE RESPONSES TO PESTS AND PATHOGENS

Abstract

Disease resistance has developed and evolved in plants to many pathogens and pests. Lack of resistance often results in poor yields and quality, and in extreme cases plant disease contributes to food shortages and famine. Today, disease resistance provides the ability to reduce requirements for pesticides that may negatively impact food prices, trade, environment, and health. Isolation of disease resistance genes in the last few years has provided considerable information on the host-pathogen interaction at the molecular level. For example, positional cloning of the Verticillium wilt disease resistance genes from tomato identified cell surface receptors with many features found in related proteins. A common, structural feature of almost all disease resistance (R) proteins isolated to date is the repetitive leucine-rich (LRR) domain that contains leucines or other hydrophobic amino acids at regular intervals within the consensus xxIxNLxxLxxLxLSxNxLSGxIP. Present in many cellular proteins of diverse function, the LRR probably produces a β-stand / β-turn resulting from conserved leucines (L) residing in a hydrophobic protein core while the other residues form a solvent-exposed surface likely involved in the protein-protein interactions and ligand binding. Many other features are common to R proteins, such as a central nucleotide-binding site (NBS) possibly involved in the activation of a kinase. The major application of isolated R genes to date has been in the development of disease resistant varieties through marker-assisted selection, and exploitation of the conserved domains to map and isolate additional alleles and R genes. Prevention of plant disease improves as our understanding of host-pathogen interactions increases and facilitates the consistent production of higher quality food.