Krishna V Subbarao

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  Available from: Krishna V Subbarao

  Article: The Sclerotinia sclerotiorum Mating Type Locus (MAT) Contains a 3.6-kb Region That Is Inverted in Every Meiotic Generation

  Periasamy Chitrampalam.¤a, Patrik Inderbitzin, Karunakaran Maruthachalam, Bo-Ming Wu¤b, Krishna V. Subbarao
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  ABSTRACT: Sclerotinia sclerotiorum is a fungal plant pathogen and the causal agent of lettuce drop, an economically important disease of California lettuce. The structure of the S. sclerotiorum mating type locus MAT has previously been reported and consists of two idiomorphs that are fused end-to-end as in other homothallics. We investigated the diversity of S. sclerotiorum MAT using a total of 283 isolates from multiple hosts and locations, and identified a novel MAT allele that differed by a 3.6-kb inversion and was designated Inv+, as opposed to the previously known S. sclerotiorum MAT that lacked the inversion and was Inv-. The inversion affected three of the four MAT genes: MAT1-2-1 and MAT1-2-4 were inverted and MAT1-1-1 was truncated at the 3’-end. Expression of MAT genes differed between Inv+ and Inv- isolates. In Inv+ isolates, only one of the three MAT1-2-1 transcript variants of Inv- isolates was detected, and the alpha1 domain of Inv+ MAT1-1-1 transcripts was truncated. Both Inv- and Inv+ isolates were self-fertile, and the inversion segregated in a 1:1 ratio regardless of whether the parent was Inv- or Inv+. This suggested the involvement of a highly regulated process in maintaining equal proportions of Inv- and Inv+, likely associated with the sexual state. The MAT inversion region, defined as the 3.6-kb MAT inversion in Inv+ isolates and the homologous region of Inv- isolates, was flanked by a 250-bp inverted repeat on either side. The 250-bp inverted repeat was a partial MAT1-1-1 that through mediation of loop formation and crossing over, may be involved in the inversion process. Inv+ isolates were widespread, and in California and Nebraska constituted half of the isolates examined. We speculate that a similar inversion region may be involved in mating type switching in the filamentous ascomycetes Chromocrea spinulosa, Sclerotinia trifoliorum and in certain Ceratocystis species.
  PLoS ONE 02/2013; 8(2):e56895-. · 4.09 Impact Factor
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  Available from: Krishna V Subbarao

  Article: The Sclerotinia sclerotiorum Mating Type Locus (MAT) Contains a 3.6-kb Region That Is Inverted in Every Meiotic Generation.

  Periasamy Chitrampalam, Patrik Inderbitzin, Karunakaran Maruthachalam, Bo-Ming Wu, Krishna V Subbarao
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  ABSTRACT: is a fungal plant pathogen and the causal agent of lettuce drop, an economically important disease of California lettuce. The structure of the mating type locus has previously been reported and consists of two idiomorphs that are fused end-to-end as in other homothallics. We investigated the diversity of using a total of 283 isolates from multiple hosts and locations, and identified a novel allele that differed by a 3.6-kb inversion and was designated Inv+, as opposed to the previously known that lacked the inversion and was Inv-. The inversion affected three of the four genes: and were inverted and was truncated at the 3'-end. Expression of genes differed between Inv+ and Inv- isolates. In Inv+ isolates, only one of the three transcript variants of Inv- isolates was detected, and the alpha1 domain of Inv+ transcripts was truncated. Both Inv- and Inv+ isolates were self-fertile, and the inversion segregated in a 1∶1 ratio regardless of whether the parent was Inv- or Inv+. This suggested the involvement of a highly regulated process in maintaining equal proportions of Inv- and Inv+, likely associated with the sexual state. The inversion region, defined as the 3.6-kb inversion in Inv+ isolates and the homologous region of Inv- isolates, was flanked by a 250-bp inverted repeat on either side. The 250-bp inverted repeat was a partial that through mediation of loop formation and crossing over, may be involved in the inversion process. Inv+ isolates were widespread, and in California and Nebraska constituted half of the isolates examined. We speculate that a similar inversion region may be involved in mating type switching in the filamentous ascomycetes and in certain species.
  PLoS ONE 01/2013; 8(2):e56895. · 4.09 Impact Factor
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  Available from: Karunakaran Maruthachalam

  Article: Colonization of spinach by Verticillium dahliae and effects of pathogen localization on the efficacy of seed treatments.

  Krishna V Subbarao, Karunakaran Maruthachalam, Steven J Klosterman, Amy G Anchieta, Beiquan Mou
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  ABSTRACT: Verticillium wilt on spinach (Spinacia oleracea L.) is caused by the soilborne fungus, Verticillium dahliae. The pathogen is seedborne and transmission through seed is a major concern because of the dispersal of the pathogen to areas where fresh and processing spinach crops are grown in rotation with susceptible crops. Reduction in seedborne inoculum minimizes pathogen spread, and therefore knowledge of pathogen localization in seed is critical to develop methods to reduce seedborne inoculum. Spinach seedlings were inoculated with conidial suspensions of a green fluorescent protein (GFP)-tagged strain of V. dahliae and colonization events were followed through seed production by confocal laser- scanning microscopy. Between 24 to 96 hr post-inoculation (PI), conidia germinated and formed hyphal colonies on root tips and in root elongation zones. Hyphae colonized root cortical tissues both intra and intercellularly by two wk and colonized the taproot xylem with abundant mycelia and conidia that led to vascular discoloration coincident with foliar symptom expression by 8 wk PI. At 10 weeks PI, the xylem of the upper stem, inflorescence and spinach seed parts, including the pericarp, seed coat, cotyledons and radicle had been colonized by the pathogen, but not the perisperm (the diploid maternal tissue). Maximum concentration of the fungus was in the seed coat, the outermost layer of the vasculature. Infection of V. dahliae in spinach seed was systemic and transmissible to developing seedlings. Additional analyses indicated that fungicide and steam seed treatments reduced detectable levels of the pathogen, but did not eliminate the pathogen from the seed. This information will assist in the development of seed treatments that will reduce the seedborne inoculum transmission to crop production fields.
  Phytopathology 11/2012; · 2.80 Impact Factor
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  Available from: Krishna V Subbarao

  Article: Sources of Verticillium dahliae Affecting Lettuce.

  Zahi K Atallah, Karunakaran Maruthachalam, Krishna V Subbarao
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  ABSTRACT: ABSTRACT Since 1995, lettuce in coastal California, where more than half of the crop in North America is grown, has consistently suffered from severe outbreaks of Verticillium wilt. The disease is confined to this region, although the pathogen (Verticillium dahliae) and the host are present in other crop production regions in California. Migration of the pathogen with infested spinach seed was previously documented, but the geographic sources of the pathogen, as well as the impact of lettuce seed sparsely infested with V. dahliae produced outside coastal California on the pathogen population in coastal California remain unclear. Population analyses of V. dahliae were completed using 16 microsatellite markers on isolates from lettuce plants in coastal California, infested lettuce seed produced in the neighboring Santa Clara Valley of California, and spinach seed produced in four major spinach seed production regions: Chile, Denmark, the Netherlands, and the United States (Washington State). California produces 80% of spinach in the United States and all seed planted with the majority infested by V. dahliae comes from the above four sources. Three globally distributed genetic populations were identified, indicating sustained migration among these distinct geographic regions with multiple spinach crops produced each year and repeated every year in coastal California. The population structure of V. dahliae from coastal California lettuce plants was heavily influenced by migration from spinach seed imported from Denmark and Washington. Conversely, the sparsely infested lettuce seed had limited or no contribution to the Verticillium wilt epidemic in coastal California. The global trade in plant and seed material is likely contributing to sustained shifts in the population structure of V. dahliae, affecting the equilibrium of native populations, and likely affecting disease epidemiology.
  Phytopathology 08/2012; 102(11):1071-8. · 2.80 Impact Factor
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  Available from: Krishna V Subbarao

  Article: Verticillium tricorpus causing lettuce wilt in Japan differs genetically from California lettuce isolates

  Toshiyuki Usami, Takeshi Kanto, Patrik Inderbitzin, Mizuho Itoh, Gan Kisaki, Yoshiyuki Ebihara, Wataru Suda, Yoshimiki Amemiya, Krishna V. Subbarao
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  ABSTRACT: In January 2002, Verticillium wilt of lettuce (Lactuca sativa L.) caused by Verticillium tricorpus occurred in upland paddy fields in Hyogo Prefecture for the first time in Japan. This fungal species was first isolated from lettuce in California, USA. In the present study, the genetic relationships between the American and Japanese isolates of V. tricorpus from lettuce were analyzed to determine whether the pathogen could have migrated to Japan from the USA, the major lettuce-seed supplier for Japan. Nucleotide sequences of the rDNA internal transcribed spacer regions, as well as the genes coding for translation elongation factor 1-alpha and RNA polymerase II were compared among American and Japanese V. tricorpus isolates from lettuce. The Japanese isolates of V. tricorpus were distinct from the American. Random amplified polymorphic DNA analyses also supported this conclusion. These results demonstrated that Verticillium wilt on lettuce caused by V. tricorpus in Japan was not related to the isolates causing the disease in California. Keywords Verticillium tricorpus –Verticillium wilt–Lettuce–Phylogenetic analysis–Random amplified polymorphic DNA (RAPD)
  Journal of General Plant Pathology 04/2012; 77(1):17-23. · 0.69 Impact Factor