Exploring the Genetic Control of Lignin Biosynthesis and Carbon Sequestration

Lignin is a heteropolymer component of plant cell walls that provides structural strength and contributes to resistance to some pests and pathogens. The maize brown midrib (bm) mutants accumulate less and altered lignin relative to non-mutants. The cloning of bm2 and bm4 reveals a previously uncharacterized link between lignin biosynthesis and components of the methylation and polyglutamylation pathways. The bm2 gene encodes a functional methylene tetrahydrofolate reductase (MTHFR), and the bm4 gene encodes a functional folylpolyglutamate synthase (FPGS). We cloned the bm2 gene via traditional mapping, RNA-sequencing, and BSR-Seq (Tang et al., 2014). To clone the bm4 gene, we combined traditional mapping, Seq-Walking, and PCR-based sequencing methods (Li et al., 2015). Mutants in the bm2 and bm4 genes accumulate 7-14% less lignin in stalks than their wild-type siblings at anthesis and senescence. We confirmed the functionality of the bm2 and bm4-encoded enzymes via yeast complementation studies. In addition to cloning single-gene mutants, we are also taking a genome-wide approach to understanding lignin biosynthesis. We have phenotyped the 5,000 maize NAM RILs and 600 diverse sorghum lines for lignin content with the goal of identifying previously uncharacterized controls of lignin biosynthesis through a genome-wide association study (GWAS). We are also exploring the connection between lignin content and the carbon sequestration potential of maize and sorghum stover via similar genome-wide approaches.