Characterization of phenotypic variation and genome aberrations observed among Phytophthora ramorum isolates from diverse hosts

Abstract

BackgroundAccumulating evidence suggests that genome plasticity allows filamentous plant pathogens to adapt to changing environments. Recently, the generalist plant pathogen Phytophthora ramorum has been documented to undergo irreversible phenotypic alterations accompanied by chromosomal aberrations when infecting trunks of mature oak trees (genus Quercus). In contrast, genomes and phenotypes of the pathogen derived from the foliage of California bay (Umbellularia californica) are usually stable. We define this phenomenon as host-induced phenotypic diversification (HIPD). P. ramorum also causes a severe foliar blight in some ornamental plants such as Rhododendron spp. and Viburnum spp., and isolates from these hosts occasionally show phenotypes resembling those from oak trunks that carry chromosomal aberrations. The aim of this study was to investigate variations in phenotypes and genomes of P. ramorum isolates from non-oak hosts and substrates to determine whether HIPD changes may be equivalent to those among isolates from oaks.ResultsWe analyzed genomes of diverse non-oak isolates including those taken from foliage of Rhododendron and other ornamental plants, as well as from natural host species, soil, and water. Isolates recovered from artificially inoculated oak logs were also examined. We identified diverse chromosomal aberrations including copy neutral loss of heterozygosity (cnLOH) and aneuploidy in isolates from non-oak hosts. Most identified aberrations in non-oak hosts were also common among oak isolates; however, trisomy, a frequent type of chromosomal aberration in oak isolates was not observed in isolates from Rhododendron.ConclusionThis work cross-examined phenotypic variation and chromosomal aberrations in P. ramorum isolates from oak and non-oak hosts and substrates. The results suggest that HIPD comparable to that occurring in oak hosts occurs in non-oak environments such as in Rhododendron leaves. Rhododendron leaves are more easily available than mature oak stems and thus can potentially serve as a model host for the investigation of HIPD, the newly described plant-pathogen interaction.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4709-7) contains supplementary material, which is available to authorized users.

Long transposon-rich centromeres in an oomycete reveal divergence of centromere features in Stramenopila-Alveolata-Rhizaria lineages

“…While these drastic genome changes can be detrimental to the organism, formation of aneuploidy and polyploidy is an important strategy orchestrated by pathogens to adapt to the environment during periods of stress (56). Polyploidy and aneuploidy are prevalent in Phytophthora natural isolates and progeny from sexual reproduction (35, 57–60). Interestingly, plant hosts can induce aneuploidy of the sudden oak death pathogen P. ramorum , which enhances its phenotypic diversity and increases its adaption to the environment (59).…”

Long transposon-rich centromeres in an oomycete reveal divergence of centromere features in Stramenopila-Alveolata-Rhizaria lineages

“…While these drastic genome changes can be detrimental to the organism, formation of aneuploidy and polyploidy is an important strategy orchestrated by pathogens to adapt to the environment during periods of stress [62]. Polyploidy and aneuploidy are prevalent in Phytophthora natural isolates and in progeny from sexual reproduction [36,[63][64][65][66]. Interestingly, plant hosts can induce aneuploidy of the sudden oak death pathogen P. ramorum, which enhances its phenotypic diversity and increases its adaption to the environment [65].…”

Genomic Instability in Fungal Plant Pathogens

“…In these organisms, aneuploidy has been previously reported [37,38]. Especially interesting are the reports concerning the oomycete P. ramorum, the causal agent of Sudden Oak Death [37,39]. In those reports, it was shown that the phenotype and karyotype of strains isolated from diseased trees were different than the ones grown in vitro.…”