Dynamic Extreme Aneuploidy (DEA) in the vegetable pathogen Phytophthora capsici and the potential for rapid asexual evolution.

Jian Hu,Xili Liu,Yuxin Zhou,Kurt Lamour,Sandesh Shrestha,Joann Mudge,Tzen-Yuh Chiang

doi:10.1371/journal.pone.0227250

Abstract

Oomycete plant pathogens are difficult to control and routine genetic research is challenging. A major problem is instability of isolates. Here we characterize >600 field and single zoospore isolates of Phytophthora capsici for inheritance of mating type, sensitivity to mefenoxam, chromosome copy number and heterozygous allele frequencies. The A2 mating type was highly unstable with 26% of 241 A2 isolates remaining A2. The A1 mating type was stable. Isolates intermediately resistant to mefenoxam produced fully resistant single-spore progeny. Sensitive isolates remained fully sensitive. Genome re-sequencing of single zoospore isolates revealed extreme aneuploidy; a phenomenon dubbed Dynamic Extreme Aneuploidy (DEA). DEA is characterized by the asexual inheritance of diverse intra-genomic combinations of chromosomal ploidy ranging from 2N to 3N and heterozygous allele frequencies that do not strictly correspond to ploidy. Isolates sectoring on agar media showed dramatically altered heterozygous allele frequencies. DEA can explain the rapid increase of advantageous alleles (e.g. drug resistance), mating type switches and copy neutral loss of heterozygosity (LOH). Although the mechanisms driving DEA are unknown, it can play an important role in adaptation and evolution and seriously hinders all aspects of P. capsici research.

Highlights

The genus Phytophthora is home to many destructive and pervasive plant pathogens [1,2,3,4,5]
For more than 150 years, scientists have struggled to manage this unwieldy genus and make of it a model organism. Part of this quest has focused on the vegetable pathogen, P. capsici–a devastating pathogen of vegetables [2,3,4,5,6,7,8,9,10,11]
Mating type was assessed as previously described using known A1 and A2 mating types paired with each isolate and incubated in the dark for approximately 1 week and the zone of hyphal interface assessed under a standard light microscope for typical amphigynous oospores

Summary

Introduction

The genus Phytophthora is home to many destructive and pervasive plant pathogens [1,2,3,4,5]. Part of this quest has focused on the vegetable pathogen, P. capsici–a devastating pathogen of vegetables [2,3,4,5,6,7,8,9,10,11].

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Conclusion