Abstract
Fusarium graminearum (F. graminearum) can cause huge yield reductions and contamination of grain with deoxynivalenol (DON), and thus is one of the most problematic pathogen of wheat worldwide. Although great efforts have been paid and great achievements have been made to control the pathogens, there is still a wide gap for understanding the mechanism underlying F. graminearum resistance. Plant LACCASEs (LACs) catalyze the oxidative polymerization of monolignols by reinforcing cell-wall of various cell types to provide mechanical support, xylem sap transportation, and defense against pest and pathogens. To date, little has been known about LAC genes in bread wheat and their potential roles in wheat-F. graminearum interaction. Through systematic analysis of the genome-wide homologs and transcriptomes of wheat, a total of 95 Triticum aestivum laccases (TaLACs) were identified, and 14 of them were responsive to F. graminearum challenge. 3D structure modelings of the 14 TaLAC proteins showed that only TaLAC78 contains the entire activity center for oxidation and the others lack the type 1 copper ion ligand (T1Cu). Both amino acid sequence alignment and three-dimensional reconstruction after amino acid mutation showed that the loss of T1Cu is not only related to variation of the key amino acid coordinating T1Cu, but also closely related to the flanking amino acids. Significantly differential temporal expression patterns of TaLACs suggested that their subfunctionalization might occur. Promoter array analysis indicated that the induction of TaLACs may be closely associated with salicylic acid signaling, dehydration, and low-oxygen stress under F. graminearum infection. Molecular docking simulation demonstrated that TaLACs can not only catalyze lignin as a substrate, but also interact with DON, which may be docked into the binding position of the monolignols, where the LACs recognize substrates. The current study provides clues for exploring the novel functions of TaLACs in wheat resistance to F. graminearum, and TaLACs maybe candidates for conferring a high level of resistance against F. graminearum in wheat.
Highlights
Fusarium head blight (FHB) is a worldwide serious wheat fungal disease that is mainly caused by Fusarium species complex (Bai and Shaner, 2004; Dean et al, 2012)
These 17 Triticum aestivum laccases (TaLACs) were unevenly distributed on wheat genome, which were located on homologous chromosomes 1, 3, 4, and 6
The total number of BOX II-like sequence, MBSI, and GC motif on the 17 FHBresponsive TaLAC promoters accounted for approximately one-third of the number of these elements on the 95 TaLACs promoters. These results suggest that the responses of the 17 TaLACs might be closely associated with salicylic acid signaling, dehydration, and anaerobic stress due to F. graminearum infection, which was consistent with the reports that salicylic acid can improve the resistance of wheat and other plants to F. graminearum (Makandar et al, 2010, 2012; Li et al, 2021)
Summary
Fusarium head blight (FHB) is a worldwide serious wheat fungal disease that is mainly caused by Fusarium species complex (Bai and Shaner, 2004; Dean et al, 2012). The combination of cell-wall composition and lignification plays a pivotal role in host resistance to FHB (Lahlali et al, 2016). Lignin is the second most abundant complex biological polymer on our planet after cellulose and an integral part of plant secondary cell wall (O’Leary, 2020). Lignin deposition in the fungus-infected cells limits the ingress of pathogens and prevents the transfer of water and nutrients from plant to pathogen to restrict pathogen growth (Hu et al, 2018). Laccases (LACs, benzenediol oxygen reductases, EC 1.10.3.2) are necessary for lignin polymerization during secondary cell wall formation (Berthet et al, 2011; Zhao et al, 2013). The report of LACs in FHB resistance is scarce, and only a preliminary study has been reported (Soni et al, 2020)
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