Genomic and transcriptomic insights into Raffaelea lauricola pathogenesis

Yucheng Zhang,Jason A Smith,Junli Zhang,Jeffrey A Rollins,Dan Vanderpool

doi:10.1186/s12864-020-06988-y

Abstract

BackgroundLaurel wilt caused by Raffaelea lauricola is a lethal vascular disease of North American members of the Lauraceae plant family. This fungus and its primary ambrosia beetle vector Xyleborus glabratus originated from Asia; however, there is no report of laurel wilt causing widespread mortality on native Lauraceae trees in Asia. To gain insight into why R. lauricola is a tree-killing plant pathogen in North America, we generated and compared high quality draft genome assemblies of R. lauricola and its closely related non-pathogenic species R. aguacate.ResultsRelative to R. aguacate, the R. lauricola genome uniquely encodes several small-secreted proteins that are associated with virulence in other pathogens and is enriched in secondary metabolite biosynthetic clusters, particularly polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS) and PKS-NRPS anchored gene clusters. The two species also exhibit significant differences in secreted proteins including CAZymes that are associated with polysaccharide binding including the chitin binding CBM50 (LysM) domain. Transcriptomic comparisons of inoculated redbay trees and in vitro-grown fungal cultures further revealed a number of secreted protein genes, secondary metabolite clusters and alternative sulfur uptake and assimilation pathways that are coordinately up-regulated during infection.ConclusionsThrough these comparative analyses we have identified potential adaptations of R. lauricola that may enable it to colonize and cause disease on susceptible hosts. How these adaptations have interacted with co-evolved hosts in Asia, where little to no disease occurs, and non-co-evolved hosts in North America, where lethal wilt occurs, requires additional functional analysis of genes and pathways.

Highlights

Laurel wilt caused by Raffaelea lauricola is a lethal vascular disease of North American members of the Lauraceae plant family
The two species were previously sequenced [37] from mate-pair and paired-end libraries generated by Illumina Hi-Seq 2000 and assembled (GenBank assembly accession: GCA_ 002778145.1 and GenBank assembly accession: GCA_ 002777955.1) by ALLPATHS-LG [38]
While R. lauricola is presumed to have originated in Asia and introduced to North America around 2002, R. aguacate PL1004 was isolated from a dead avocado tree in Miami-Dade County, Florida in 2009 [35] and has been isolated subsequently from the mycangia of Xyleborus bispinatus collected from avocado trees [94]

Summary

Introduction

Laurel wilt caused by Raffaelea lauricola is a lethal vascular disease of North American members of the Lauraceae plant family. This fungus and its primary ambrosia beetle vector Xyleborus glabratus originated from Asia; there is no report of laurel wilt causing widespread mortality on native Lauraceae trees in Asia. In North America, X. glabratus was first detected in Port Wentworth, Georgia, USA in 2002 [4] and the wilting and mortality of native Lauraceae trees in the area were first reported in 2003 [5]. Infection of this domesticated and agronomically important Lauraceae family member has significantly impacted the commercial production of avocado in Florida [13] and poses a serious threat to currently

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