Zhang, Juan , Subramanian, Senthil , Zhang, Yansheng , Yu, Oliver .
Flavone synthases from Medicago truncatula are flavanone-2-hydroxylases and are important for nodulation.
Flavones are important co-pigments found in the flowers of many higher plants and play a variety of roles in plant adaptation to stress. In Medicago species, flavones also act as signal molecules during symbiotic interaction with the diazotropic bacterium Sinorhizobium meliloti. They are the most potent nod gene inducers found in root exudates. However, flavone synthase (FNS II), the key enzyme responsible for flavone biosynthesis has not been characterized in Medicago species. We cloned two FNS II genes from M. truncatula using known FNS II sequences from other species and named them MtFNSII-1 and MtFNSII-2. Functional assays in yeast suggested that the catalytic mechanisms of both cytochrome P450 monooxygenases are similar to the other known legume FNS II from Glycyrrhiza echinata. MtFNSII converted flavanones to 2-hydroxyflavanones instead of flavones where as FNS II from the non-legume Gerbera hybrida, converted flavanones to flavones directly. The two MtFNSII genes have distinct tissue-specific expression patterns. MtFNSII-1 is highly expressed in roots where as MtFNSII-2 is highly expressed in flowers and siliques. In addition, MtFNSII-2 is inducible by S. meliloti and methyl jasmonate treatment, where as MtFNSII-1 is not. Histochemical staining of transgenic hairy roots carrying the promoter-reporter constructs indicated that the MtFNSII-2 induction is tissue-specific, mostly localized to vascular tissues and root hairs. RNA interference-mediated suppression of MtFNSII genes resulted in flavone depleted roots and led to significantly reduced nodulation when inoculated with S. meliloti. Our results provide genetic evidence supporting that flavones are important for nodulation in M. truncatula.
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1 - Donald Danforth Plant Science Center
2 - Donald Danforth Plant Science Center, 975 N Warson Rd, St Louis, MO, 63132, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM