Fusarium Head Blight Responsive Transcriptional Reprogramming in Four Wheat Genotype

Fusarium head blight (FHB) is caused mostly by the ascomycetous fungus Fusarium graminearum (Fg) and causes severe reduction in yield and quality of wheat grain in North America. Multiple avenues of research have been coordinated to tackle this epidemics in Canada and across the world. Under the Canadian Wheat Alliance, the National Research Council Canada and Agriculture and Agri-Food Canada have joined forces to investigate transcriptomics dynamics of four wheat genotypes (Nyubai, Wuhan 1, HC374, and Shaw), at 2 and 4 days post inoculation (dpi) with Fg, using RNA-seq technology. Our result shows a global transcriptional reprograming to mobilize the defense machinery in wheat hosts upon the challenge by Fg inoculation. Protein serine/threonine kinases and LRR-RK were associated with susceptibility at 2 dpi, while ethylene-responsive, WRKY, Myb, bZIP, NAC-domain containing and other types of transcription factors were associated with susceptibility at 4 dpi. In the resistant genotypes, Glutathione S-transferase (GST), membrane proteins and distinct LRR-RKs were associated with FHB resistance across the three genotypes. Genes with unique, high up-regulation induced by Fg in Wuhan 1 were mostly transiently expressed at 2 dpi, while many defense-associated genes were up-regulated at both 2 and 4 dpi in Nyubai; the majority of unique genes up-regulated in HC374 were detected at 4 dpi only. Differences in expression profiles among the resistant genotypes indicate genotype-specific defense mechanisms. This study also shows a greater resemblance in transcriptomics of HC374 to Nyubai, consistent with their sharing of two FHB resistant QTLs on 3BS and 5AS, compared to Wuhan 1 which carries one QTL on 2DL in common with HC374. In the pathogen, most genes showed increased expression between 2 and 4 dpi in all genotypes, with stronger levels in the susceptible host; however two pectate lyases and a hydrolase were expressed higher at 2 dpi, and acetyltransferase activity was highly enriched at 4 dpi.