02705nas a2200193 4500008004100000245014100041210006900182260003900251300001100290490000600301520203400307100001802341700002202359700001302381700002102394700002002415700002302435856005302458 2012 eng d00aPhenotypic diversification Is associated with host-induced transposon derepression in the sudden oak death pathogen Phytophthora ramorum0 aPhenotypic diversification Is associated with hostinduced transp bPublic Library of Sciencec04/2012 ae347280 v73 a

The oomycete pathogen Phytophthora ramorum is responsible for sudden oak death (SOD) in California coastal forests. P. ramorum is a generalist pathogen with over 100 known host species. Three or four closely related genotypes of P. ramorum (from a single lineage) were originally introduced in California forests and the pathogen reproduces clonally. Because of this the genetic diversity of P. ramorum is extremely low in Californian forests. However, P. ramorum shows diverse phenotypic variation in colony morphology, colony senescence, and virulence. In this study, we show that phenotypic variation among isolates is associated with the host species from which the microbe was originally cultured. Microarray global mRNA profiling detected derepression of transposable elements (TEs) and down-regulation of crinkler effector homologs (CRNs) in the majority of isolates originating from coast live oak (Quercus agrifolia), but this expression pattern was not observed in isolates from California bay laurel (Umbellularia californica). In some instances, oak and bay laurel isolates originating from the same geographic location had identical genotypes based on multilocus simples sequence repeat (SSR) marker analysis but had different phenotypes. Expression levels of the two marker genes analyzed by quantitative reverse transcription PCR were correlated with originating host species, but not with multilocus genotypes. Because oak is a nontransmissive dead-end host for P. ramorum, our observations are congruent with an epi-transposon hypothesis; that is, physiological stress is triggered on P. ramorum while colonizing oak stems and disrupts epigenetic silencing of TEs. This then results in TE reactivation and possibly genome diversification without significant epidemiological consequences. We propose the P. ramorum-oak host system in California forests as an ad hoc model for epi-transposon mediated diversification.

1 aKasuga, Takao1 aKozanitas, Melina1 aBui, Mai1 aHüberli, Daniel1 aRizzo, David, M1 aGarbelotto, Matteo uhttp://dx.doi.org/10.1371%2Fjournal.pone.0034728