Genomic basis of sex determination and avirulence in the Hessian fly (Mayetiola destructor).

摘要

The Hessian fly, Mayetiola destructor (Say), is one of the most destructive insect pests of wheat (Triticum spp.), causing significant losses to US agriculture every year. This insect is a member of the economically important gall midge (Cecidomyiidae) family in the order Diptera. It serves as an excellent model for studying plant-insect interactions, especially those involving gene-for-gene interactions. Knowledge about the underlying molecular mechanism of these interactions in insects is still scarse, because insect avirulence (Avr) genes and their cognate resistance (R) genes have not been identified. Valuable information has been gained in the past decade in this field of study, mainly from plant-pathogen systems. The research presented in this study was focused in the two major topics related to this insect pest: (1) understanding the genomic basis of post-zygotic chromosome elimination in sex determination; and (2) test the gene-for-gene hypothesis by attempting to discover the Avr gene (vH9) that corresponds to the R gene H9 in wheat. The content of this thesis is divided into three chapters. Chapter one introduces some of the general aspects of the biology and importance of the Hessian fly. Chapter two discusses in detail the genetic and physical mapping of a genetic factor Cm (Chromosome maintenance), that has a maternal effect and controls post-zygotic chromosome elimination during sex determination. Chapter three describes the fine-scale mapping of the vH9 Avr gene within a 176 kb sequence region on the short arm of chromosome X1 and the discovery of candidate vH9 genes. The best candidate gene had polymorphisms that co-segregated with virulence to H9 and presented features resembling the Avr genes of oomycetes. The information generated from this study is expected to facilitate the discovery of new avirulence genes both in Hessian fly and in closely related insect species, contribute to the identification of the corresponding resistance gene products in the host plant, and help us to better understand the processes involved in the evolution of sex determination mechanisms in different organisms. As a consequence of this study, improved strategies to control this insect pest may be developed, and it may be possible to use diagnostics to monitor for virulence, as well as to engineer plants conferring a more efficient and durable source of resistance against the evolution of virulent genotypes.