Identification and Characterization of Victorin Sensitivity in Arabidopsis thaliana

Abstract

Cochliobolus victoriae is a necrotrophic fungus that produces a host-selective toxin called victorin. Victorin is considered to be host selective because it has been known to affect only certain allohexaploid oat cultivars containing the dominant Vb gene. Oat cultivars containing Vb are also the only genotypes susceptible to C. victoriae. Assays were developed to screen the "nonhost" plant of C. victoriae, Arabidopsis thaliana, for victorin sensitivity. Sensitivity to victorin was identified in six of 433 bulk populations of Arabidopsis. In crosses of Col-4 (victorin-insensitive) x victorin-sensitive Arabidopsis ecotypes, victorin sensitivity segregated as a single dominant locus, as it does in oats. This Arabidopsis locus was designated LOV, for locus orchestrating victorin effects. Allelism tests indicate that LOV loci are allelic or closely linked in all six victorin-sensitive ecotypes identified. LOV was localized to the north arm of Arabidopsis thaliana chromosome I. The victorin-sensitive Arabidopsis line LOV1 but not the victorin-insensitive line Col-4 was susceptible to C. victoriae infection. Consequently, the LOV gene appears to be a genetically dominant, disease susceptibility gene.

Plant disease susceptibility conferred by a “resistance” gene

“…Col-4, Ws, and mutant lines, jar1-1 (39), npr1-1 (40), ein2-1 (41), pad3 (42), and NahG (23), all in Col-0, were obtained from the Ohio State University Arabidopsis Biological Resource Center (Columbus, OH). LOV1 (16) and Col-LOV (36) were generated in our laboratory. Other seeds were obtained from the following individuals: Sainsbury Laboratory [eds1-1 Ws (43) (24)], and J. Chang [rar1-1 (25)].…”

“…A locus conferring disease susceptibility to C. victoriae in Arabidopsis, called LOV1, was mapped to the interval between Nga63 and NCCI on Chromosome 1 (16). We fine-mapped LOV1, using an additional 200 victorininsensitive F 2 progeny of a cross between a victorin-sensitive line, LOV1 (ecotype Cl-0), and victorin-insensitive Col-4.…”

“…During infection of oat and Arabidopsis, C. victoriae develops appressoria and penetrates tissue of compatible hosts, but in incompatible plant genotypes, fungal penetration stops following appressorium development (16,32). Analysis of C. victoriae infection of oat suggests that the fungus may penetrate host tissue before host cells are dying, implying the fungus does not merely gain nutrients from dead or dying cells (32).…”

“…Victoria-type oats are allohexaploid and not readily amenable to molecular genetic studies. However, identification of victorin sensitivity and Victoria blight susceptibility in Arabidopsis thaliana (16) has enabled our investigation of this disease susceptibility pathway. We report similarities between this susceptibility response and disease resistance, including identification of the susceptibility locus, LOV1, as a coiled-coil NBS-LRR, R gene family member.…”

MED18 interaction with distinct transcription factors regulates multiple plant functions

“…This data confirmed that elevated expression of GRX and TRX genes contribute to the enhanced susceptibility of the med18 and yy1 mutants to fungal infection. Arabidopsis grxs13 mutant exhibits enhanced resistance to B. cinerea 26 , whereas the trx-h5 mutant is insensitive to the victorin toxin produced by the necrotrophic fungus Cochliobolus victoriae 27 . Interestingly, TRX-h5 is a direct virulence target for the victorin toxin 28 .…”