Molecular Plant-Microbe Interactions (Nov 2012)

A Polyketide Synthase Gene, ACRTS2, Is Responsible for Biosynthesis of Host-Selective ACR-Toxin in the Rough Lemon Pathotype of Alternaria alternata

  • Y. Izumi,
  • K. Ohtani,
  • Y. Miyamoto,
  • A. Masunaka,
  • T. Fukumoto,
  • K. Gomi,
  • Y. Tada,
  • K. Ichimura,
  • T. L. Peever,
  • K. Akimitsu

DOI
https://doi.org/10.1094/MPMI-06-12-0155-R
Journal volume & issue
Vol. 25, no. 11
pp. 1419 – 1429

Abstract

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The rough lemon pathotype of Alternaria alternata produces host-selective ACR-toxin and causes Alternaria leaf spot disease of rough lemon (Citrus jambhiri). The structure of ACR-toxin I (MW = 496) consists of a polyketide with an α-dihydropyrone ring in a 19-carbon polyalcohol. Genes responsible for toxin production were localized to a 1.5-Mb chromosome in the genome of the rough lemon pathotype. Sequence analysis of this chromosome revealed an 8,338-bp open reading frame, ACRTS2, that was present only in the genomes of ACR-toxin-producing isolates. ACRTS2 is predicted to encode a putative polyketide synthase of 2,513 amino acids and belongs to the fungal reducing type I polyketide synthases. Typical polyketide functional domains were identified in the predicted amino acid sequence, including β-ketoacyl synthase, acyl transferase, methyl transferase, dehydratase, β-ketoreductase, and phosphopantetheine attachment site domains. Combined use of homologous recombination-mediated gene disruption and RNA silencing allowed examination of the functional role of multiple paralogs in ACR-toxin production. ACRTS2 was found to be essential for ACR-toxin production and pathogenicity of the rough lemon pathotype of A. alternata.