Abstract
BackgroundAs effects of global climate change intensify, the interaction of biotic and abiotic stresses increasingly threatens current agricultural practices. The secondary cell wall is a vanguard of resistance to these stresses. Fusarium thapsinum (Fusarium stalk rot) and Macrophomina phaseolina (charcoal rot) cause internal damage to the stalks of the drought tolerant C4 grass, sorghum (Sorghum bicolor (L.) Moench), resulting in reduced transpiration, reduced photosynthesis, and increased lodging, severely reducing yields. Drought can magnify these losses. Two null alleles in monolignol biosynthesis of sorghum (brown midrib 6-ref, bmr6-ref; cinnamyl alcohol dehydrogenase, CAD; and bmr12-ref; caffeic acid O-methyltransferase, COMT) were used to investigate the interaction of water limitation with F. thapsinum or M. phaseolina infection.ResultsThe bmr12 plants inoculated with either of these pathogens had increased levels of salicylic acid (SA) and jasmonic acid (JA) across both watering conditions and significantly reduced lesion sizes under water limitation compared to adequate watering, which suggested that drought may prime induction of pathogen resistance. RNA-Seq analysis revealed coexpressed genes associated with pathogen infection. The defense response included phytohormone signal transduction pathways, primary and secondary cell wall biosynthetic genes, and genes encoding components of the spliceosome and proteasome.ConclusionAlterations in the composition of the secondary cell wall affect immunity by influencing phenolic composition and phytohormone signaling, leading to the action of defense pathways. Some of these pathways appear to be activated or enhanced by drought. Secondary metabolite biosynthesis and modification in SA and JA signal transduction may be involved in priming a stronger defense response in water-limited bmr12 plants.
Highlights
As effects of global climate change intensify, the interaction of biotic and abiotic stresses increasingly threatens current agricultural practices
We identified coexpression modules enriched for protein turnover, signal transduction, and primary and secondary metabolism that potentially contribute to the enhanced disease response in bmr12
Responses of bmr12 and wild-type plants to inoculation with stalk pathogens F. thapsinum and M. phaseolina Well-watered and water limited Tx430 wild-type and near-isogenic bmr6 and bmr12 plants at anthesis were wound-inoculated at the peduncle with F. thapsinum, M. phaseolina, or potato dextrose broth (PDB) between anthesis and seed set
Summary
As effects of global climate change intensify, the interaction of biotic and abiotic stresses increasingly threatens current agricultural practices. Fusarium thapsinum (Fusarium stalk rot) and Macrophomina phaseolina (charcoal rot) cause internal damage to the stalks of the drought tolerant C4 grass, sorghum (Sorghum bicolor (L.) Moench), resulting in reduced transpiration, reduced photosynthesis, and increased lodging, severely reducing yields. 1947 are fungal stalk pathogens of sorghum that can cause lodging and result in yield loss, especially under drought. These fungi are causal agents of Fusarium stalk rot and charcoal rot, respectively. Stalk rots are the most damaging diseases to production with incidence up to 100% in some fields [12], which can lead to lodging and significant biomass losses due to harvesting difficulties [13]
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