Identification and characterization of stilbene derivatives in infected sorghum seedlings

Abstract

We have previously identified a pathogen-inducible stilbene synthase gene (SbSTS1) in sorghum. In vitro enzyme assays of recombinant SbSTS1 demonstrated that trans-resveratrol was a reaction product when p-coumaroylCoA was used as a substrate. In transgenic Arabidopsis plants over-expressing SbSTS1, cis-piceid was found as the major stilbene metabolite. Here we use a combination of mass spectrometric methods (precursor ion scan, product ion scan, multiple reaction monitoring) to identify stilbene derivatives in sorghum seedlings following inoculation with the anthracnose pathogen Colletotrichum graminicola. Results indicated that trans-piceid accumulates predominantly in infected seedlings, together with a resveratrol acetyl-hexoside. Interestingly trans-piceid accumulation was considerably higher in a sorghum cultivar that does not produce the 3-deoxyanthocyanidin phytoalexins. In vitro bioassays showed that trans-piceid is less toxic than trans-resveratrol toward C. graminicola. The role of trans-piceid accumulation in sorghum disease resistance will be discussed.