Induction of defense gene homologues in wheat roots during interactions with Pseudomonasfluorescens

Specific strains of Pseudomonas fluorescens directly inhibit soilborne fungal pathogens of Triticum aestivum (wheat) during colonization of the wheat rhizosphere, but until now the impact of these beneficial bacteria on wheat gene expression was unknown. To test the hypothesis that P. fluorescens induces defense genes in wheat roots, we constructed a custom microarray of 192 oligonucleotides representing 84 wheat root expressed sequence tags (ESTs) homologous to defense/stress genes from Arabidopsis, tomato, rice, and barley, and 11 candidate root developmental genes. The ESTs were selected from existing wheat root EST libraries. Arrays were interrogated with Alexa Fluor 546-labeled transcript (cDNA) populations from roots or coleoptiles of cultivar Finley or lines 442 or 443, near-isogenic for the cold temperature-dependent vrn1A flowering locus, four days after seed inoculation with the take-all-suppressive strain P. fluorescens Q8r1-96. Twenty-two transcripts encoding Ca2+-dependent protein kinases, components of the oxidative stress, cold stress and jasmonic acid pathways, and proteins associated with the hypersensitive response were induced or repressed in wheat roots during P. fluorescens interactions. Transcripts encoding pathogenesis-related protein Pr-10a and hypersensitive response protein HRin1 also were induced in coleoptiles. Real-time PCR demonstrated that eleven transcripts were induced in root tissue between 2 and 6 h and remained elevated at 24 h post-inoculation. Our findings suggest that biocontrol P. fluorescens modulates defense/stress gene expression in wheat roots.