Evolutionary Developmental Biology (Evo-Devo)
Chandra, Ambika , Huff, David .
A Molecular Mechanism for Induced Hermaphroditism Caused by Parasitic Castration.
Parasitic castration is a disease affecting animals, mollusks, insects, and plants where host gonads are sterilized preventing evolution of host resistance and redirecting resource allocation. A fascinating illustration of parasitic castration is the alteration of sex in dioecious buffalograss caused by pistil smut fungus inducing the development of female sex organs in male plants, making them hermaphrodite. How and why fungi induce hermaphroditism in their hosts is unknown. Here we show that pistil smut induces hermaphroditism in male buffalograss by down-regulating a female-sterility gene homologous to Tasselseed2 (Ts2). This molecular mechanism is supported by temporal and spatial expression analyses performed using quantitative real time PCR and in situ hybridization, respectively, on a cloned full length buffalograss Ts2 homolog. In addition, pistil smut infection enhances overall sexual reproductive allocation (SRA) in both male and female sex forms of buffalograss. In female plants, the fungus induces an 11.8-fold increase in ovary production while in male plants the fungus induces a 1.9-fold increase in flower number. Phylogenetic analyses of morphology and rDNA sequences show that pistil smut is clearly distinct from any other species of Tilletia suggesting that it may not even be a species of Tilletia anymore. The unusually large genetic distance of pistil smut from Tilletia clade indicates an accelerated rate of evolution possibly be due to pistil smutís long term coevolutionary struggle with its host culminating in induced hermaphroditism. Overall, we speculate that Ts2 initially evolved its female sterility function as a host defense mechanism and that induced hermaphroditism by pistil smut represents an over-riding virulence mechanism.
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1 - Pennsylvania State University, Crop and Soil Sciences, 116 Agricultural Sciences and Industries Building, University Park, PA, 16802, USA
Presentation Type: Poster:Posters for Topics
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM