THE ACTIVATION OF THE POTATO PR-LOA GENE REQUIRES THE PHOSPHORYLATIONOF THE NUCLEAR FACTOR PBF-1

The pathogenesis-related gene PR-10a (formerly STH-2) is induced in va rious organs of potato after wounding, elicitor treatment, or infectio n by Phytophthora infestans. Deletion analysis of the promoter of the PR-10a gene enabled us to identify a 50-bp region, located between pos itions -155 and -105, necessary for the elicitor responsiveness of the beta-glucuronidase reporter gene in transgenic potato plants. Within this region, a 30-bp sequence, located between positions -135 and -105 , was necessary for the activation of the promoter by the elicitor. Ho wever, strong promoter activity after elicitor treatment required the presence of a 20-bp sequence located between positions -155 and -135. The region between -135 and -105 was specifically recognized by two nu clear factors, PBF-1 (PR-10a Binding Factor 1) and PBF-2, and binding of PBF-1 was coordinated with the accumulation of the PR-10a mRNA, Gel shift assays using nuclear extracts pretreated with sodium deoxychola te or alkaline phosphatase suggested that PBF-1 is a multimeric factor in which at least one of the constituent proteins can be phosphorylat ed, Treatment with alkaline phosphatase also indicated that binding of PBF-1 is positively regulated by phosphorylation and that it is phosp horylated only in tissues in which PR-10a is expressed. The use of pro tein phosphatase and kinase inhibitors in vivo provided additional evi dence that wounding and elicitor treatment induce the phosphorylation of PBF-1 and that this phosphorylation is associated with gene activat ion.