Genome analysis of the ubiquitous boxwood pathogen Pseudonectria foliicola

Authors: RIVERA, YAZMIN - Animal And Plant Health Inspection Service (APHIS); SALGADO-SALAZAR, CATALINA - Oak Ridge Institute For Science And Education (ORISE); VELTRI, DANIEL - National Institutes Of Health (NIH); MALAPI-WIGHT, MARTHA - Animal And Plant Health Inspection Service (APHIS); Crouch, Jo Anne

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2018
Publication Date: 8/21/2018
Citation: Rivera, Y., Salgado-Salazar, C., Veltri, D., Malapi-Wight, M., Crouch, J. 2018. Genome analysis of the ubiquitous boxwood pathogen Pseudonectria foliicola. PeerJ. 6:e5401. https://doi.org/10.7717/peerj.5401.
DOI: https://doi.org/10.7717/peerj.5401

Interpretive Summary: Boxwood plants are affected by many different diseases caused by fungi. Some boxwood diseases are deadly and quickly kill the infected plants, but with others, the plant can survive and even thrive when infected. The fungus that causes volutella blight is the most common of these weak boxwood pathogens. Even the healthiest boxwood plants are infected by the volutella fungus, and often there are no signs that the plants are hurt by the infection. In order to understand why the volutella blight fungus is such a weak pathogen and to understand the genetic mechanisms it uses to interact with boxwood, the complete genome of the volutella fungus was sequenced and characterized. The genome was exceptionally small, and contained relatively few genes for disease. In addition, many genes associated with lower disease levels were present in the genome sequence. These findings and the genome datasets will be used by scientists working to understand why some diseases are only able to cause damage to weak plants.

Technical Abstract: Boxwood (Buxus spp.) are broad-leaved, evergreen landscape plants valued for their longevity and ornamental qualities. Volutella leaf and stem blight, caused by the ascomycete fungi Pseudonectria foliicola and P. buxi, is one of the major diseases affecting the health and ornamental qualities of boxwood. Although this disease is less severe than boxwood blight caused by Calonectria pseudonaviculata and C. henricotiae, its widespread occurrence and disfiguring symptoms have caused substantial economic losses to the ornamental industry. In this study, we sequenced the genome of P. foliicola isolate ATCC13545 using Illumina technology and compared it to other publicly available fungal pathogen genomes to better understand the biology of this organism. A de novo assembly estimated the genome size of P. foliicola at 28.7 Mb (425 contigs; N50 = 184,987 bp; avg. coverage 188×), with just 9,272 protein-coding genes. To our knowledge, P. foliicola has the smallest known genome within the Nectriaceae. Consistent with the small size of the genome, the secretome, CAzyme and secondary metabolite profiles of this fungus are reduced relative to two other surveyed Nectriaceae fungal genomes: Dactylonectria macrodidyma JAC15-245 and Fusarium graminearum Ph-1. Interestingly, a large cohort of genes associated with reduced virulence and loss of pathogenicity was identified from the P. foliicola dataset. These data are consistent with the latest observations by plant pathologists that P. buxi and most likely P. foliicola, are opportunistic, latent pathogens that prey upon weak and stressed boxwood plants.