Research Article

Horizontal gene transfer of Fhb7 from fungus underlies Fusarium head blight resistance in wheat

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Science  22 May 2020:
Vol. 368, Issue 6493, eaba5435
DOI: 10.1126/science.aba5435
  • Fhb7 confers FHB resistance by detoxifying trichothecenes.

    (A) Fhb7 in Th. elongatum genome likely came from an Epichloë fungus through horizontal gene transfer. Fhb7 drives FHB resistance when introgressed from Thinopyrum into wheat. (B) Fhb7 encodes a GST that detoxifies Fusarium-produced trichothecenes by conjugating GSH (blue) to the epoxy group (red). R1 to R5 refer to the variable groups in trichothecenes.

  • Fig. 1 Genome evolution of Th. elongatum and cloning of Fhb7.

    (A) Maximum likelihood phylogenetic tree of the genomes of Triticeae species and the Ks distributions of ortholog genes between the E genome and the wheat Chinese Spring A, B, and D subgenomes. mya, million years ago. (B) Syntenic blocks between the E genome and the three wheat subgenomes. The representative inversion fragment is indicated in green; chromosomal translocations for the wheat A subgenome compared with the E genome are also indicated in blue. (C) Map-based cloning of Fhb7 at the distal region of chromosome 7E. Using the BC6F1 population derived from the cross between two wheat-Thinopyrum substitution lines, 7E1/7D and 7E2/7D, Fhb7 was initially mapped to an interval between the markers XsdauK79 and XsdauK80 (~1.2 Mb on the E reference genome) (second bar from the top). The expressed genes are labeled as follows: gray refers to no expression in the E reference genome; blue refers to E reference genome–specific expression; orange refers to expression in the E reference, 7E1 and 7E2 genomes; red refers to expression in FHB-resistant donor genomes of 7E2 and E reference (third bar from the top). BAC clones containing Tel7E01T1020600.1 were identified from the substitution line 7E2/7D, based on which genetic markers (XsdauK86 and XsdauK87) were developed for recombinant screening of the CS ph1bph1b population. Finally, Fhb7 was genetically confirmed within a 245-kb region between markers XsdauK86 and XsdauK88, with only the candidate gene Tel7E01T1020600.1 encoding a GST [CDS is shown in red; untranslated region is shown in gray] (fourth bar from the top). (D) FHB was evaluated for wild-type (WT, KN199) and transgenic wheat KN199 expressing the native promoter and the 846-bp open reading frame of Fhb7. T3 plants containing Fhb7 from three different lines were evaluated for FHB resistance using single floret inoculation (35). The FHB was scored for at least five spikes per repeat, with at least three repeats for each transgenic line.

  • Fig. 2 Fhb7 confers FHB resistance by detoxifying DON.

    (A) Maximum likelihood phylogenetic tree of the closest homologs of Fhb7 from plants and fungi. The DNA sequence similarity with Fhb7 is marked in red. (B) Horizontal gene transfer of Fhb7. The transcripts CDS (purple), and possible untranslated regions (yellow) of Fhb7 are shown along chromosome 7E, and the sequence sharing high similarity with the E. aotearoae genome is presented as a gray block. The genomic fragment (897 bp) containing full CDS and partial untranslated region of Fhb7 showed 97% identity between the two genomes. (C) DON tolerance of Fhb7-transgenic wheat. Seedlings (4 days old) were moved to a petri dish containing 25 mg L−1 DON and seedling length was evaluated 7 d after the DON treatment at room temperature. (D) Extracted ion chromatograms (EICs) at m/z 604.2173 revealing the presence of two DON-glutathione adducts. The Fhb7 NIL, Fhb7-transgenic wheat, and Fhb7-transgenic yeast (P. pastoris) cultures were treated with 25 mg L−1 DON for 24 hours. A product that elutes at 1.68 min accumulated in Fhb7(+) samples and a known, nonenzymatically produced DON-glutathione adduct product that elutes at 2.4 min accumulated in the corresponding Fhb7(–) control samples. (E) Relative abundances of the de-epoxidated Fhb7-catalyzed DON-glutathione (green) adduct and the known nonenzymatic DON-glutathione adduct (blue) in spikes of Fusarium-challenged NIL plants contrasting in Fhb7. After inoculation of F. graminearum on spike glumes, the Fhb7(+) NIL accumulated a copious amount of de-epoxidated DON-glutathione adduct. By contrast, the DON substrate reduced the accumulation in Fhb7(+) NIL compared with that in Fhb7(–) NIL, as shown in the bottom bar chart. (F) Molecular structure of the de-epoxidated DON-glutathione adduct catalyzed by Fhb7.

  • Fig. 3 Application prospects for Fhb7 in wheat resistance breeding.

    (A) Genomic in situ hybridization analysis (left panel) showing a translocation of the distal region of 7E (containing Fhb7) from an E genome donor into wheat. Scale bar, 20 μm. Also shown are images of Fusarium-infected spikes (middle panel) and crown rot (right panel) of LX99 NILs contrasting in Fhb7. (B) FHB resistance of Fhb7 in eight different wheat genetic backgrounds evaluated at 21 d after inoculation in field conditions. (C) Crown rot phenotypes were recorded as the death ratio after growth in soil containing F. pseudograminearum at 30 days postinfection. (D) Field plant photographs of two Fhb7(+) NILs and one Fhb7(–) NIL in the LX99 background. (E) Comparison of the yield traits among the two Fhb7(+) NILs and one Fhb7(–) NIL in the LX99 background evaluated in the 2017 field experiment. FLL, flag leaf length (cm); FLW, flag leaf width (cm); SL, spike length (cm); KPS, kernels per spike; IS, infertile spikelets; GL, grain length (mm); GW, grain width (mm); TGW, thousand grain weight (g). (F) Comparison of the grain yield among eight Fhb7 translocation lines in different wheat genetic backgrounds. The grain yield was measured from a 1-m2 plot in the 2017 and 2018 field experiments.

  • Table 1 Summary statistics for Th. elongatum genome assembly.

    Assembly characteristicsValues
    Estimated genome size4.78 Gb
    Total length of contigs4.58 Gb
    N50 length of contigs2.15 Mb
    Total number of contigs12,262
    Longest contigs11.6 Mb
    Total length of scaffolds4.63 Gb
    N50 length of scaffolds73.24 Mb
    Total number of scaffolds783
    Longest scaffolds258.71 Mb
    Total gap size52.78 Mb
    Total sequences anchored to the pseudochromosomes4.54 Gb
    Number of annotated high-confidence genes44,474
    Percentage of repeat sequences81.29%
    Complete BUSCOs97.6%
    Fragmented BUSCOs1.3%
    Missed BUSCOs1.1%

Supplementary Materials

  • Horizontal gene transfer of Fhb7 from fungus underlies Fusarium head blight resistance in wheat

    Hongwei Wang, Silong Sun, Wenyang Ge, Lanfei Zhao, Bingqian Hou, Kai Wang, Zhongfan Lyu, Liyang Chen, Shoushen Xu, Jun Guo, Min Li, Peisen Su, Xuefeng Li, Guiping Wang, Cunyao Bo, Xiaojian Fang, Wenwen Zhuang, Xinxin Cheng, Jianwen Wu, Luhao Dong, Wuying Chen, Wen Li, Guilian Xiao, Jinxiao Zhao, Yongchao Hao, Ying Xu, Yu Gao, Wenjing Liu, Yanhe Liu, Huayan Yin, Jiazhu Li, Xiang Li, Yan Zhao, Xiaoqian Wang, Fei Ni, Xin Ma, Anfei Li, Steven S Xu, Guihua Bai, Eviatar Nevo, Caixia Gao, Herbert Ohm, Lingrang Kong

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
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    • Tables S1 to S23
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    MDAR Reproducibility Checklist
    Data S1
    Data S2
    Data S3

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