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Journal of General Virology header logo Journal of General Virology

Volume 106, Issue 5

Novel endornaviruses infecting that attenuate vegetative growth, promote sporangia formation and confer hypervirulence to the host oomycete Open Access

Abstract

Two novel endornaviruses were found in isolated from black lesions on var. plants in a Japanese forest. These two endornaviruses were named Phytophthora cactorum alphaendornavirus 4 (PcAEV4) and Phytophthora cactorum alphaendornavirus 5 (PcAEV5) and have site-specific nick structures in their positive RNA strands, which are hallmarks of alphaendornaviruses. Ribavirin and cycloheximide treatment of the protoplasts effectively cured the host oomycete (strain Kara1) of the viruses. The resultant virus-free strain (Kara1-C) displayed abundant mycelial growth with less zoosporangia formation as compared to the Kara1 strain. Remarkably, the Kara1-C strain exhibited a reduced ability to form black lesions on leaves, suggesting that the presence of PcAEV4 and PcAEV5 in the Kara1 strain led to enhanced virulence in host plants. Under osmotic pressure and cell wall synthesis inhibition, the Kara1 strain exhibited less growth inhibition compared with the Kara1-C strain. In contrast, the Kara1 strain showed more growth inhibition in the presence of membrane-permeable surfactant compared with the Kara1-C strain, indicating that the two endornaviruses can alter the susceptibility of the host oomycete to abiotic stresses. Co-localization and cell fractionation analyses showed that PcAEV4 and PcAEV5 localized to intracellular membranes, particularly the endoplasmic reticulum membrane fraction. Furthermore, infection with these two endornaviruses was found to affect the host’s response to exogenous sterols, which enhanced vegetative growth and zoosporangia formation, as well as virulence of the host oomycete. These results provide insights into the effects of endornavirus infection in spp. and also highlight the usefulness of protoplast-based methods in advancing virus studies.

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Keyword(s): attenuation , endornavirus , hypervirulence , membrane fraction , Phytophthora and site-specific nick
Funding
This study was supported by the:
  • Japan Society for the Promotion of Science (Award 23KJ0855)
    • Principal Award Recipient: SakutaKohei
  • Japan Society for the Promotion of Science (Award 20KK0137)
    • Principal Award Recipient: HiromitsuMoriyama
© 2025 The Authors
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License.
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2025-05-01
2026-01-22

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Novel endornaviruses infecting Phytophthora cactorum that attenuate vegetative growth, promote sporangia formation and confer hypervirulence to the host oomycete
J. Gen. Virol. 106, 002099 (2025); https://doi.org/10.1099/jgv.0.002099
/content/journal/jgv/10.1099/jgv.0.002099
/content/journal/jgv/10.1099/jgv.0.002099
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