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

Author: mycolabadmin
5/1/2025
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Summary

Researchers discovered two new viruses infecting a plant-damaging organism called Phytophthora cactorum. When these viruses are present, the organism grows more slowly but becomes more aggressive at infecting plants. The viruses attach to special membranes inside cells and depend on cholesterol-like compounds for their replication. Scientists were able to remove the viruses from infected strains using specialized techniques, allowing them to compare infected and virus-free versions of the organism.

Background

Mycoviruses infecting oomycetes have been primarily identified in Phytophthora species, which are plant pathogens causing significant agricultural damage. Endornaviruses are positive-sense RNA viruses with characteristic site-specific nick structures in their genomes. The mechanisms by which endornavirus infection affects host growth, pathogenicity, and stress responses in Phytophthora remain largely unknown due to lack of established viral curing and reinfection systems.

Objective

To identify and characterize novel endornaviruses infecting Phytophthora cactorum isolates and determine their effects on host vegetative growth, zoosporangia formation, virulence, and stress susceptibility. The study aimed to establish protoplast-based methods for viral curing and investigate the molecular mechanisms of endornavirus-host interactions.

Results

PcAEV4 and PcAEV5 are novel alphaendornaviruses with genomes of 12,839 nt and 12,774 nt respectively, containing site-specific nicks characteristic of alphaendornaviruses. Viral-infected Kara1 strain showed attenuated mycelial growth but enhanced zoosporangia formation and increased virulence on plant leaves compared to virus-cured Kara1-C strain. Co-infection altered host susceptibility to osmotic stress and surfactants, localized to endoplasmic reticulum membranes, and enhanced virulence through altered response to exogenous sterols.

Conclusion

This study demonstrates that PcAEV4 and PcAEV5 co-infection significantly modulates host oomycete phenotype by attenuating vegetative growth while promoting zoosporangia formation and hypervirulence. The findings provide insights into endornavirus-host interactions in Phytophthora and highlight the importance of intracellular membranes and sterols in endornavirus replication and host pathogenicity, establishing protoplast-based methods as valuable tools for oomycete virus research.

Published in:Journal of General Virology,
Study Type:Laboratory Research Study,
Source: PMID: 40310668, doi: 10.1099/jgv.0.002099