The brown midrib (bmr) mutants prevent stalk rots under drought conditions and improve sorghum biomass quality

Authors: Funnell-Harris, Deanna; Sattler, Scott; Toy, John; O`Neill, Patrick; Khasin, Maya

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/7/2023
Publication Date: 6/6/2023
Citation: Funnell-Harris, D.L., Sattler, S.E., Toy, J.J., Oneill, P.M., Khasin, M. 2023. The brown midrib (bmr) mutants prevent stalk rots under drought conditions and improve sorghum biomass quality. Presented at: Sorghum in the 21st Century, Global Sorghum Conference, Montpelier, France, June 5 – 9, 2023. Meeting Abstract Book. p. 142.

Interpretive Summary:

Technical Abstract: Lignin provides rigidity to cell walls and a barrier against pathogens but decreases biomass digestibility. Sorghum bmr increases digestibility for livestock and bioenergy uses. Loss-of-function mutations in Bmr2, Bmr6, and Bmr12 encoding monolignol biosynthetic enzymes 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, and a caffeic acid O-methyltransferase, respectively, result in reduced lignin levels and increased digestibility. Surprisingly, near-isogenic bmr2, bmr6 and bmr12 well-watered greenhouse-grown plants were equally or more resistant to Fusarium stalk rot (Fusarium thapsinum) and charcoal rot (Macrophomina phaseolina) than their corresponding wild-type. Because sorghum is vulnerable to stalk rots during drought, we developed a greenhouse protocol to evaluate lines for disease responses under water-deficit conditions. Under water deficit, near-isogenic bmr2, bmr6 and bmr12 lines were equally or more resistant to the two stalk pathogens than their corresponding wild-type. Three alleles of Bmr19 that encodes a folylpolyglutamate synthase in 1-carbon metabolism, one allele of Bmr30 that encodes chalcone isomerase in flavonoid biosynthesis, and two alleles from unidentified genes (Bmr29 and Bmr31) were incorporated into three parental lines to develop near-isogenic lines. Most bmr lines were as resistant to the stalk pathogens as their corresponding wild-type. Under water-deficit condition, wild-type BTx623 was highly susceptible to M. phaseolina, while near-isogenic bmr29-1 and bmr31-1 lines were as resistant as counterparts grown under well-watered conditions. Following F. thapsinum and M. phaseolina inoculations, bmr12 showed increased salicylic and jasmonic acids, phytohormones involved in defense signaling, than the wild-type, using targeted metabolomics; bmr12 also showed increased induction of defense genes under water deficit, using RNA-sequencing, indicating that drought conditions primed bmr12 for pathogen defense. These studies provide evidence that impairing lignin synthesis does not weaken sorghum defenses against fungal pathogens, and bmr mutants may be valuable for development of hybrids with increased resistance to pathogens and drought for improved stover quality and usability.