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A Virus in a Fungus in a Plant: Three-Way Symbiosis Required for Thermal Tolerance

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Science  26 Jan 2007:
Vol. 315, Issue 5811, pp. 513-515
DOI: 10.1126/science.1136237

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  1. Fig. 1.

    Presence or absence of CThTV in different strains of C. protuberata, detected by ethidium bromide staining (A), Northern blot using RNA 1 (B) and RNA 2 (C) transcripts of the virus as probes, and RT-PCR using primers specific for a section of the RNA 2 (D). The isolate of the fungus obtained by sectoring was made virus-free (VF) by freezing-thawing. The virus was reintroduced into the virus-free isolate through hyphal anastomosis (An) with the wild type (Wt). The wild-type isolate of the fungus sometimes contains a subgenomic fragment of the virus that hybridizes to the RNA 1 probe (arrow).

  2. Fig. 2.

    (Top) Representative D. lanuginosum plants after the heat-stress experiment with thermal soil simulators. Rhizosphere temperature was maintained at 65°C for 10 hours and 37°C for 14 hours/day for 14 days under greenhouse conditions. Plants were nonsymbiotic (NS) and symbiotic with the wild-type virus-infected isolate of C. protuberata (Wt), the hygromycin-resistant isolate newly infected with the virus through hyphal anastomosis (An), or the virus-free hygromycin-resistant isolate (VF). (Bottom) The histogram presents the number of plants chlorotic, dead, and alive at the end of the experiment. The small letters on top of the bars indicate statistical differences or similarities (chi-square test, P <0.01).

  3. Fig. 3.

    (A) Anastomosis of the wild-type virus-infected isolate of C. protuberata (Wt) and the virus-free hygromycin-resistant isolate (VF) to produce a virus-infected hygromycin-resistant isolate (An). (B) After singlespore isolation to produce pure cultures, the isolate newly infected with the virus (An) retained the hygromycin-resistance and the morphology of the VF isolate.

  4. Fig. 4.

    (Top) Representative tomato (Solanum lycopersicon, var. Rutgers) plants after the heat-stress experiment. Plants were nonsymbiotic (NS) and symbiotic with the wild-type virus-infected isolate of C. protuberata (Wt), the hygromycin-resistant isolate newly infected with the virus through hyphal anastomosis (An) or the virus-free hygromycin-resistant isolate (VF). Rhizosphere temperature was maintained at 65°C for 10 hours and ambient temperature (26°C) for 14 hours/day for 14 days under greenhouse conditions. (Bottom) The histogram presents the number of plants dead (white) and alive (black) at the end of the experiment. The small letters on top of the bars indicate statistical differences or similarities (Fisher's exact test, P <0.05).