Response of Sorghum Enhanced in Monolignol Biosynthesis to Stalk Rot Pathogens

Abstract

To increase phenylpropanoid constituents and energy content in the versatile C4 grass sorghum (Sorghum bicolor [L.] Moench), sorghum genes for proteins related to monolignol biosynthesis were overexpressed: SbMyb60 (transcriptional activator), SbPAL (phenylalanine ammonia lyase), SbCCoAOMT (caffeoyl coenzyme A [CoA] 3-O-methyltransferase), Bmr2 (4-coumarate:CoA ligase), and SbC3H (coumaroyl shikimate 3-hydroxylase). Overexpression lines were evaluated for responses to stalk pathogens under greenhouse and field conditions. Greenhouse-grown plants were inoculated with Fusarium thapsinum (Fusarium stalk rot) and Macrophomina phaseolina (charcoal rot), which cause yield-reducing diseases. F. thapsinum-inoculated overexpression plants had mean lesion lengths not significantly different than wild-type, except for significantly smaller lesions on two of three SbMyb60 and one of two SbCCoAOMT lines. M. phaseolina-inoculated overexpression lines had lesions not significantly different from wild-type except one SbPAL line (of two lines studied) with mean lesion lengths significantly larger. Field-grown SbMyb60 and SbCCoAOMT overexpression plants were inoculated with F. thapsinum. Mean lesions of SbMyb60 lines were similar to wild-type, but one SbCCoAOMT had larger lesions, whereas the other line was not significantly different than wild-type. Because overexpression of SbMyb60, Bmr2, or SbC3H may not render sorghum more susceptible to stalk rots, these lines may provide sources for development of sorghum with increased phenylpropanoid concentrations.

Large scale genome-wide association study reveals that drought induced lodging in grain sorghum is associated with plant height and traits linked to carbon remobilisation

“…bmr lines) can provide the same level of or higher resistance to Fusarium spp. and Macrophomina phaseolina than sorghum lines with normal lignin content (Funnell-harris et al , 2010, 2014, 2017, 2018, 2019). This might be due to the inhibition the infection of stalk rotting pathogens by cell-wall-bound phenolic compounds from monolignol biosynthesis that can induce defensible pathways (Funnell-harris et al , 2017).…”

Lignin Metabolic Engineering in Grasses for Primary Lignin Valorization

“…The results suggested that heterologous expression of AtMYB61 in rice increased the lignin content mainly by enriching S units as well as p-coumarate and tricin moieties in the lignin polymers 17) . Studies with S. bicolor aiming to increase energy content in biomass plants were also reported; lignin content was augmented by overexpression of a S. bicolor transcriptional activator, SbMYB60, in Sorghum 38,39) . In addition, lignin content of 30 Indonesian S. bicolor accessions was analyzed and high lignincontent accessions were identified 13) .…”

“…These strategies to increase lignin content and simplify lignin structures are also applicable to large-sized grass biomass plants, such as Sorghum, Panicum (switchgrass), Miscanthus and Erianthus. Recently, an increase in the energy content in biomass plants was achieved by the manipulation of S. bicolor F5H (CAld5H) expression 40) as well as the lignin content augmentation by SbMYB60 overexpression in S. bicolor 38,39) and isolation of high-lignin content S. bicolor accessions 13) .…”