Genomic signatures of heterokaryosis in the oomycete pathogen Bremia lactucae

Kyle Fletcher, Juliana Gil, Lien D. Bertier, Aubrey Kenefick, Kelsey J. Wood, Lin Zhang, Sebastian Reyes-Chin-Wo, Keri Cavanaugh, Cayla Tsuchida, Joan Wong, Richard W Michelmore

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce globally. This oomycete is highly variable and rapidly overcomes resistance genes and fungicides. The use of multiple read types results in a high-quality, near-chromosome-scale, consensus assembly. Flow cytometry plus resequencing of 30 field isolates, 37 sexual offspring, and 19 asexual derivatives from single multinucleate sporangia demonstrates a high incidence of heterokaryosis in B. lactucae. Heterokaryosis has phenotypic consequences on fitness that may include an increased sporulation rate and qualitative differences in virulence. Therefore, selection should be considered as acting on a population of nuclei within coenocytic mycelia. This provides evolutionary flexibility to the pathogen enabling rapid adaptation to different repertoires of host resistance genes and other challenges. The advantages of asexual persistence of heterokaryons may have been one of the drivers of selection that resulted in the loss of uninucleate zoospores in multiple downy mildews.

Original languageEnglish (US)
Article number2645
JournalNature communications
Issue number1
StatePublished - Dec 1 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)


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