Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2009
Publication Date: September 1, 2009
Citation: Upchurch, R.G., Ramirez, M.E. 2009. Defense gene induction in soybean seeds after infection with Cercospora kikuchii and Diaporthe phaseolorum. Phytopathology, 99:S132.
We measured the expression levels of seven pathogen defense genes in detached soybean seeds after controlled inoculation with mycelial suspensions of Cercospora kikuchii (CK), causal agent of purple seed-stain and leaf blight and Diaporthe phaseolorum var. meridionales (DPM), causal agent of southern stem canker and seed decay, in order to gain insight into intrinsic basal host defense in developing seeds. Expression of defense genes in pathogen and mock-inoculated green seeds, harvested 35 days after flowering, was monitored over a 48 h post-inoculation period during which both pathogens grew in seed tissue around the site of inoculation. Gene expression measured by RT-qPCR and normalized to soybean actin revealed that five of the seven genes were upregulated in seed by CK and DPM with four of the seven, pathogenicity-related protein 1 (PR1), matrix metalloproteinase 2 (MMP2), chalcone synthase (CHS) and phenylalanine ammonia-lyase (PAL) strongly upregulated. Beta 1-3 endoglucanase (PR2) was weakly upregulated by CK, and lipoxygenase 7 (LOX7) was weakly upregulated by DPM. LOX7 was induced earlier at 24 h by CK treatment. Results show that the pattern and magnitude of induction of these defense genes in soybean seeds was different for Cercospora and Diaporthe, but both pathogens elicited a remarkably high expression (55 to 161 fold over the control) of the metrix metalloproteinase (MMP2) gene by 48 h post inoculation.