Mutational Analysis of a Wheat O-methyltransferase Involved in Flavonoid Metabolism

Methylated flavones, and tricin in particular, have been implicated in protecting wheat plants against a variety of biotic and abiotic stresses. Methylated flavones are produced via O-methylation of the hydroxyl groups in flavones, which is catalyzed by O-methyltransferases (OMTs). To examine the role of wheat OMT2 in methylated flavone biosynthesis and facilitate interrogation of tricin functions in wheat-environment interactions, loss-of-function mutants of OMT2 homoeologs, omt-A2 and omt-B2, were identified from a tetraploid wheat Targeting Induced Local Lesions in Genomes (TILLING) mutant population and crossed to generate the omt-A2 omt-B2 double mutant. Although tricin and most other soluble phenolics did not differ in leaves and glumes of TILLING control and the omt-A2, omt-B2, and omt-A2 omt-B2 mutants, chlorogenic acid was increased in glumes of omt-A2 omt-B2 relative to TILLING control, suggesting that it might serve as a substrate for OMT2. The omt2 mutant lines showed similar growth phenotypes as well as comparable lignin deposition in cell walls of stems compared to TILLING control. These results collectively suggest that OMT2 and its close homolog OMT1 may possess overlapping activities in tricin production, with OMT1 compensating for the missing OMT2 activities in the omt2 mutant lines.