Histology and RNA Sequencing Provide Insights Into Fusarium Head Blight Resistance in AAC Tenacious

Abstract

Fusarium head blight (FHB) is a serious fungal disease affecting wheat and other cereals worldwide. This fungus causes severe yield and quality losses from a reduction in grain quality and contamination of grain with mycotoxins. Intensive breeding efforts led to the release of AAC Tenacious, which was the first spring wheat cultivar registered in Canada with a resistant (R) rating to FHB. To elucidate the physiological mechanisms of resistance, we performed histological and transcriptomic analyses of AAC Tenacious and a susceptible control Roblin after inoculation with Fusarium graminearum (Fg). The spikelet and rachis of infected wheat spikes were hand sectioned and monitored by confocal and fluorescent microscopy. Visible hyphae were observed within the inoculated spikelets for AAC Tenacious; however, the infection was largely restricted to the point of inoculation (POI), whereas the adjacent florets in Roblin were heavily infected. Significant cell wall thickening within the rachis node below the POI was evident in AAC Tenacious compared to Roblin in response to Fg inoculation. Rachis node and rachilla tissues from the POI and the rachis node below the POI were collected at 5 days post inoculation for RNAseq. Significant changes in gene expression were detected in both cultivars in response to infection. The rachis node below the POI in AAC Tenacious had fewer differentially expressed genes (DEGs) when compared to the uninoculated control, likely due to its increased disease resistance. Analysis of DEGs in Roblin and AAC Tenacious revealed the activation of genes and pathways in response to infection, including those putatively involved in cell wall modification and defense response.

Untargeted Metabolomics Reveals a Multi-Faceted Resistance Response to Fusarium Head Blight Mediated by the Thinopyrum elongatum Fhb7E Locus Transferred via Chromosome Engineering into Wheat

“…The defence response of the same resistant plants induced at 4 dpi was characterised by a significantly more complex interplay between finely tuned and correlated metabolic pathways (Figure 12), clearly highlighting that several metabolic routes are associated with the FHB resistance conferred by the Fhb7E locus. This is in agreement with reports on rachis metabolic and transcriptomic analyses of other loci conferring FHB resistance to durum and bread wheat, including Fhb1 and Fhb2 of the Sumai 3 derivation [26,27,51], genes/QTL from Canadian bread and durum wheat germplasm [24,53] and the same Th. elongatum Fhb7E locus considered in the present work [69,70].…”

“…Mycotoxins, of which the most commonly detected in FHB-affected wheat is deoxynivalenol (DON), are virulence factors that Fusarium pathogens produce, which, after floral invasion and hyphal spreading, reach the rachis node. Consistent evidence (e.g., [ 23 , 24 ] and references therein) indicates this spike section, together with the rachilla [ 25 ], as crucial for subsequent spike colonization by the fungus. It is at this level, in fact, that a main switch between a susceptible and a resistant host response occurs.…”

Linking Multi-Omics to Wheat Resistance Types to Fusarium Head Blight to Reveal the Underlying Mechanisms

“…For example, transcinnamate 4-monooxygenase, a CYP450 involved in the pathway of lignin biosynthesis, catalyzes the oxidative reaction of trans-cinnamic acid to p-coumaric acid [136]. Several other studies have reported that CYP450s were expressed during FHB infection [69,133,137,138]. However, transcripts of one CYP450 gene accumulated only in resistant wheats and not in susceptible ones in response to F. graminearum compared to water controls [139].…”

Deep Learning Genome-wide Linkage Association Study for Wheat Fusarium Head Blight Resistance Genes Discovery

“…RNA-seq data from AAC Tenacious and Roblin generated by Kirby et al (2020) [54] were downloaded from NCBI. AAC Tenacious is the only spring wheat cultivar in Canada to receive a resistant rating to FHB, and belongs to the Canada Prairie Spring Red market class.…”