Pathogenesis-related proteins and their genes in cereals

Pathogenesis-related proteins (PR-proteins) are induced in plants in respon se to attack by microbial or insect pests. They have been classified into s everal groups (PR-1 through PR-14 at present) based on their amino acid seq uences and biochemical functions. Many of these proteins that have been pur ified from infected plants or seed extracts possess antifungal or insectici dal activity. Genes and cDNA clones for all classes of PR-proteins have bee n isolated from a variety of cereals. Some of these genes/cDNAs have been u sed to transform cereals. This review presents a summary of the PR-proteins and their genes characterized from rice, wheat, barley, sorghum and maize. Efforts to improve disease or insect resistance of these cereal plants by genetic engineering using genes for PR-proteins also are discussed. In many cases, the expression of the PR-proteins either singly or in combination a ppears to improve resistance to fungi or insects. In addition, chromosomal location of the PR-protein genes indicates that members of the same family of PR-protein genes or sometimes even several families of PR-protein genes often are clustered in the cereal genome, suggesting coordinate regulation. Some of these PR-protein genes map closely to quantitative traits loci. So me concerns regarding the use of genes encoding PR-proteins for genetic mod ification of cereals also are addressed.