Spatial and temporal expression patterns of Avr1b-1 and defense-related genes in soybean plants upon infection with Phytophthora sojae.

The Avr1b locus is required for avirulence of the oomycete pathogen Phytophthora sojae on soybeans carrying resistance gene Rps1b. One of the Avr genes of the locus (Avr1b-1) was shown to encode an elicitor. We have analyzed the spatial and temporal expression patterns of Avr1b-1 in comparison to defense-related genes induced in soybean. Avr1b-1 expression was detectable mainly in close proximity to the site of infection, in wound-inoculated hypocotyls as well as in roots infected with zoospores. Usually, in compatible interactions, higher expression levels of Avr1b-1 were observed in roots when compared with incompatible P. sojae-soybean interactions, whereas neither the timing nor the amount of transcript accumulation of defense-related genes showed cultivar-specific differences. In contrast, the PsojNIP gene encoding a proposed virulence factor was expressed only during the necrotrophic phase in the compatible interaction.