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 P.sojNIP gene encoding a proposed virulence factor was expressed only during the necrotrophic phase in the compatible interaction.
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