BTH induces elevated hydrolytic enzyme activity, expression of two members of the PR1 gene family, and resistance to Phytophthora palmivora in papaya. Twenty five additional papaya genes showing elevated systemic expression 3 days after BTH treatment have now been identified by suppression subtraction hybridization, and confirmed and quantified by northern blots and quantitative RT-PCR. These genes include several PR genes and related genes known from other systems to have direct anti-microbial activities, and two genes with likely involvement in altering cell wall porosity and lignification. Additionally, six genes with potential roles in establishing reducing conditions following the oxidative burst are induced, including three not previously known to have defense related roles: CPBI 6, a 2-oxoglutarate-dependent oxygenase (2OG-Fe(II) oxygenase), CPBI 14, a malate oxidoreductase, and CPBI 16, a hydroxyphenylpyruvate dioxygenase (HPPDase). Specific Cys residues required for redox activation of arabidopsis NPR1 are conserved in papaya NPR1. Together with the induction of the several genes with potential roles in establishing reducing conditions, this suggests that the regulation of cellular redox status may play a role in SAR induction in papaya.
