Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2008
Publication Date: December 1, 2008
Repository URL: http://hdl.handle.net/10113/32683
Citation: Palmer, N.A., Sattler, S.E., Saathoff, A.J., Funnell-Harris, D.L., Pedersen, J.F., Sarath, G. 2008. Genetic background impacts soluble and cell wall-bound aromatics in brown midrib mutants of sorghum. Planta 229 (1): 115-127 Interpretive Summary: Sorghum can serve as an important model and forage for bioenergy purposes. Mutations in lignin biosynthesis (a cell wall polymer), collectively known as the brown midribs (bmr) are commonly used to breed for sorghum plants with better value as a forage. In this study we have evaluated for the first time some of the biochemical characteristics of two bmr alleles singly or in combination in two different sorghum genetic backgrounds. Our data indicate a strong background effect and suggest that matching bmr alleles with the appropriate sorghum background could lead to the development of sorghum plants with greater biofuel potential.
Technical Abstract: To evaluate the effects that genetic background has on two sorghum brown midrib (bmr) mutants, plant phenolics, lignin biosynthetic enzymes and stem anatomy were evaluated in wild-type (WT), bmr-6, bmr-12 and double-mutants (bmr-6 and bmr-12) in near isogenic , RTx430 and Wheatland backgrounds. There was considerable variation in HPLC profiles of soluble fractions obtained from younger internodes versus older internodes. GCMS revealed that differences in levels of free phenolic acids were associated with the genetic background of both bmr loci. In near-isogenic Wheatland double-mutants, free ferulic acid (FA) was present in much greater amounts than p-coumaric acid (4CA) in RTx430 double-mutant plants, phenolic acid profiles were more similar to those found in RTx430 bmr-12 plants. Cell wall bound 4CA was reduced to a much greater extent in the bmr plants than wall bound FA. Interestingly, in the double mutant lines, incorporation of 4CA into cell walls of the Wheatland double mutant more closely resembled the Wheatland bmr-6 plants. In contrast, the RTx430 double mutants possessed wall-bound 4CA levels that were more similar to the RTx430 bmr-12 plants. The staining intensity of stem section, observed through light microscopy, indicated that lignification of cortical sclerenchyma and vascular bundle fibers were decreased in bmr-6 > bmr-12 > double mutant plants relative to WT. Immunoblots of stem extracts showed that caffeoyl-O-methyl transferase protein was nearly absent in bmr-12 and double mutant plants and was present in bmr-6 and wild type plants. Levels of immunoreactive cinnamyl alcohol dehydrogenase and caffeoyl-CoA-O-methyl transferase protein did not appear to be altered in any genotype.