PHOTOACTIVATED PSORALENS ELICIT DEFENSE GENES AND PHYTOALEXIN PRODUCTION IN THE PEA PLANT

In the pea plant (Pisum sativum), compounds that intercalate into DNA induce the production of similar to 20 major proteins similar to the p attern induced during nonhost disease resistance to the bean fungal pa thogen, Fusarium solani f,sp, phaseoli, The pea phytoalexin, pisatin, as well as RNA homologous to several disease-resistance response (DRR) genes accumulate following treatment with these compounds, Psoralen w as chosen to characterize this interaction further because it intercal ates into DNA and, following irradiation with 365 mm UV light (UV365), forms covalent bonds with pyrimidines on either or both strands of DN A, This produces monoadducts or crosslinks, respectively, Dose experim ents showed that 60 mu g/ mL 4'-aminomethyl-4,5',8-trimethylpsoralen f ollowed by 18 J/cm(2) UV365 was sufficient to produce an accumulation of pisatin similar to that produced in response to the fungus, Under t hese inducing conditions, there was an average of 0.19 adducts per kb of pea genomic DNA. The accumulation of pisatin and the RNA of several DRR genes by psoralen required photoactivation, which suggests that c ovalent binding to DNA was necessary for induction. As the promoters o f several putative fungal-induced pea genes contain long stretches of d(AT)(n), which is the preferred psoralen photobinding site, restricti on fragments spanning DRR genes were examined after in vivo psoralen t reatment. The rate of crosslinking was compared between fungal-induced and noninduced genes using a modified Southern blot analysis. Implica tions of the induction of the DRR due to psoralen binding are discusse d.