Sorghum brown midrib19 (Bmr19) gene links lignin biosynthesis to folate metabolism

Authors: ADEYANJU, ADEDAYO - Purdue University; Sattler, Scott; RICH, PATRICK - Purdue University; RIVERA-BURGOS, LUIS - North Carolina State University; XU, XIAOCHEN - Purdue University; EJETA, GEBISA - Purdue University

Submitted to: Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2021
Publication Date: 4/28/2021
Citation: Adeyanju, A.O., Sattler, S.E., Rich, P.J., Rivera-Burgos, L.A., Xu, X., Ejeta, G. 2021. Sorghum brown midrib19 (Bmr19) gene links lignin biosynthesis to folate metabolism. Genes. 12(5):660. https://doi.org/10.3390/genes12050660.
DOI: https://doi.org/10.3390/genes12050660

Interpretive Summary: Sorghum is an important forage crop in the U.S., which is also being developed as a bioenergy feedstock for renewable fuels and chemicals. Lignin is a component of cell walls, and its presence causes the biomass to be resistance to conversion in the digestive systems of livestock or chemical conversion processes. The brown midrib (bmr) mutants of sorghum and other grasses are associated with reduced amounts of lignin within their cell walls. The gene that when mutated caused bmr19 was identified using next generation sequencing technology. The gene encodes an enzyme involved in folate metabolism, which provides a critical cofactor required for lignin synthesis. The research underscores the importance of folate metabolism for lignin synthesis in sorghum and other plants, and demonstrates that bmr19 is useful for impairing both pathways to improve sorghum forage for conversion.

Technical Abstract: Genetic analysis of brown midrib sorghum (Sorghum bicolor) mutant lines assembled in our program has previously shown that the mutations fall into four allelic groups, bmr2, bmr6, bmr12 or bmr19. Causal genes for allelic groups bmr2, bmr6 and bmr12, have since been identified. In this report, we provide evidence for the nature of the bmr19 mutation. This was accomplished by introgressing each of the four bmr alleles into nine different genetic backgrounds. Polymorphisms from four resequenced bulks of sorghum introgression lines containing either mutation, relative to those of a resequenced bulk of the nine normal midrib recurrent parent lines, were used to locate their respective causal mutations. The analysis confirmed the previously reported causal mutations for bmr2 and bmr6 but failed in the case of bmr12-bulk due to a mixture of mutant alleles at the locus among members of that mutant bulk. In the bmr19-bulk, a common G ' A mutation was found among all members in Sobic.001G535500. This gene encodes a putative folylpolyglutamate synthase with high homology to maize Bm4. The brown midrib phenotype co-segregated with this point mutation in two separate F2 populations. Furthermore, an additional variant allele at this locus obtained from a TILLING population also showed a brown midrib phenotype, confirming this locus as Bmr19.