Effects of altering three steps of monolignol biosynthesis on sorghum responses to stalk pathogens and water deficit

Authors: Funnell-Harris, Deanna; Sattler, Scott; O`Neill, Patrick; Gries, Tammy; GE, ZHENGXIANG - University Of Nebraska; NERSESIAN, NATALY - University Of Nebraska

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2023
Publication Date: 12/1/2023
Citation: Funnell-Harris, D.L., Sattler, S.E., Oneill, P.M., Gries, T.L., Ge, Z., Nersesian, N. 2023. Effects of altering three steps of monolignol biosynthesis on sorghum responses to stalk pathogens and water deficit. Plant Disease. 107:3984-3995. https://doi.org/10.1094/PDIS-08-22-1959-RE.
DOI: https://doi.org/10.1094/PDIS-08-22-1959-RE

Interpretive Summary: Lignin synthesis plays a critical role in plant defenses against pathogens. The sorghum stalk diseases Fusarium stalk rot and charcoal rot are major impediments to biomass yield and quality, especially during drought. Sorghum lines were developed that either were impaired or augmented in three different steps of lignin synthesis. Lines impaired in lignin synthesis were not more prone to these diseases under adequate water, but plants with brown midrib (bmr) 2 and bmr12 plants were more resistant to the pathogen during drought than normal plants. Lines with augmented activity of the three enzymes similarly did not have increased stalk diseases under drought conditions, and one line overexpressing the Bmr2 gene was more resistant than normal plants under adequate water conditions. Information obtained from this research will be valuable for producing sorghum hybrids for the production of biofuels and renewable chemicals uses, while still maintaining resistance to stalk diseases, especially during drought.

Technical Abstract: The drought resilient crop sorghum [Sorghum bicolor (L.) Moench] is grown worldwide for multiple uses, including forage or potential lignocellulosic bioenergy feedstock. A major impediment to biomass yield and quality are the pathogens, Fusarium thapsinum and Macrophomina phaseolina, which cause Fusarium stalk rot and charcoal rot, respectively. These fungi are more virulent with abiotic stresses such as drought. Monolignol biosynthesis plays a critical role in plant defense. The genes Brown midrib -6 (Bmr6), Bmr12 and Bmr2 encode the monolignol biosynthesis enzymes cinnamyl alcohol dehydrogenase, caffeic acid O-methyltransferase and 4-coumarate:CoA ligase, respectively. Lines overexpressing these genes or the corresponding bmr mutants were screened for pathogen responses with controlled adequate or deficit watering. Additionally, near-isogenic bmr12 and wild-type lines in five backgrounds were screened for response to F. thapsinum with adequate and deficit watering. All mutant and overexpression lines were no more susceptible than corresponding wild-type under both watering conditions. The bmr2 and bmr12 lines, near-isogenic to wild-type, had significantly shorter mean lesion lengths than RTx430 wild-type when inoculated with F. thapsinum with water deficit. Additionally, bmr2 plants grown under water deficit had significantly smaller mean lesions when inoculated with M. phaseolina than under adequate water conditions. When well-watered, bmr12 in Wheatland and one of two Bmr2 overexpression lines in RTx430 had shorter mean lesion lengths than corresponding wild-type lines. This research demonstrates that modifying monolignol biosynthesis for increased usability may not impair plant defenses but can even enhance resistance to stalk pathogens under drought conditions.