COORDINATED EXPRESSION OF DEFENSE-RELATED GENES BY TMV INFECTION OR SALICYLIC-ACID TREATMENT IN TOBACCO

To understand the coordinated functions of the different classes of de fense-related genes expressed in plant disease resistance, the express ion patterns of pathogenesis related (PR) protein genes and genes invo lved in antioxidation and the production of secondary metabolites were examined. The expression patterns of the respective defense-related g enes were monitored following TMV infection or salicylic acid treatmen t, Northern blot analyses showed that PR genes such as PR-1, beta-1,3- glucanase and chitinase were strongly induced ire tobacco leaves upon TMV infection or salicylic acid treatment, 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and phenylalanine ammonialyase (PAL), involved in isoprenoid and phenylpropanoid biosynthesis, respectively, were mildl y induced at the late stage of normal hypersensitive response (HR) or after salicylic acid treatment when compared with the PR-gene expressi ons. However, in acute HR, they were strongly expressed at the early s tage. Interestingly, the expression of the antioxidative genes, anioni c peroxidase anal ascorbate peroxidase, were inversely expressed follo wing TMV infection and salicylic acid treatment. Differential expressi on of 3 groups of genes involved in plant defense responses are discus sed in relation to different signal transduction pathways.