Ana Saballos1, Gebisa Ejeta2, ChulHee Kang3, Emiliano Sanchez3, and Wilfred Vermerris1. (1) Genetics Institute and Agronomy department, University of Florida, 1376 Mowry Road, Gainesville, FL 32610-3610, (2) Agronomy, Purdue University, 915 W. State Street, West Lafayette, IN 47907, (3) School of Molecular Biosciences, Washington State University, Pullman, WA 99164-4660
Genetic improvement of biomass crops can reduce the cost of biomass-to-ethanol conversion. Lignin content and composition affect the conversion of cellulose to monomeric sugars. Sorghum is a promising source of biomass due to its great yield potential and tolerance to stresses. The brown midrib (bmr) mutants of sorghum are characterized by brown vascular tissue and altered lignin content. We combined genetic and chemical approaches to identify four bmr loci represented by the bmr2, bmr6, bmr12 and bmr19 allelic groups. We have shown that rapid classification of novel bmr lines can be achieved using phloroglucinol-HCl as a histochemical stain. Enzymatic saccharification of stover demonstrated that the mutations in the bmr2, bmr6 and bmr12 groups can increase glucose yields up to 25% compared to wild-type isolines. Characterization of changes in subunit lignin composition in each of the groups by pyrolysis-gas chromatography-mass spectrometry helps predict the genes underlying the mutations. Chemical composition of the bmr6 group is consistent with reduction of cinnamyl alcohol dehydrogenase (CAD) activity. Analysis of the sorghum genome revealed 14 CAD-like genes. Based on their phylogenic relationship and the identification of non-conservative mutations in three allelic bmr6 lines, SbCAD2 was identified as the Bmr6 gene. In order to expedite the selection of the bmr mutant alleles in breeding populations, we have developed molecular markers specific for several bmr alleles. We are currently working on cloning additional bmr loci from bmr lines identified in a TILLING population.
