MOLECULAR MECHANISMS OF PLANT PATHOGEN INTERACTIONS IN CEREAL CROPS
Crop Production and Pest Control Research
Project Number: 3602-22000-017-00
Start Date: Apr 02, 2012
End Date: Apr 01, 2017
Objective 1: Discover and analyze the function of genes involved in pathogenicity of foliar fungal pathogens of wheat and other grain crops.
Sub-objective 1a. Provide gene-expression annotations for the approximately 44% of the genes in the M. graminicola genome that have no predicted function, particularly those that share conserved domains of unknown function in other fungi. Sub-objective 1b. Analyze genes expressed under many conditions including during early, transitional and late stages of pathogenicity to identify those that may be important for disease development and other biological processes.
Sub-objective 1c. Test the function of candidate pathogenicity genes or others involved in important biological processes by knocking out their expression and analyzing changes in phenotype.
Objective 2: Characterize the genetic and biochemical bases for resistance of wheat to the foliar fungal pathogens responsible for Septoria and Stagonospora leaf blotches. Sub-objective 2a. Analyze genes expressed at several time points after inoculation with the pathogens to identify those associated with the major-gene resistance response of wheat. Sub-objective 2b. Analyze genes expressed at several time points after inoculation with the pathogens to identify those associated with non-host resistance responses of wheat and barley. Sub-objective 2c. Test the function of candidate resistance-associated genes by virus-induced gene silencing (VIGS) or RNA interference (RNAi).
Objective 3: Develop genetic markers to be used by associated breeding programs in the development of disease-resistant germplasm of wheat and other grain crops.
Sub-objective 3a. Develop large recombinant-inbred populations segregating for the Stb2 and Stb3 genes for resistance to Septoria tritici blotch in wheat and identify additional closely linked molecular markers. Sub-objective 3b. Develop mapping populations to identify quantitative resistance against the Septoria pathogens of wheat. Sub-objective 3c. Identify and validate molecular markers linked to quantitative resistance against the Septoria pathogens of wheat.
Sub-objective 3d. Test Chinese wheat cultivars for resistance against the Septoria pathogens of wheat.
The preferred approach will be sequencing of messenger RNAs produced during several stages of pathogenesis by Mycosphaerella graminicola and Stagonospora nodorum on wheat, and of non-host resistance responses on barley. Numerous libraries will be analyzed from as many treatments as possible to obtain the greatest number of expressed genes, which was shown to be very effective in a previous analysis of EST sequences. Some treatments will consist of the pathogen exclusively in pure culture to identify genes involved in fungal development and responses to light, while others will include the pathogen in its host to identify genes involved in fungal pathogenicity and in host resistance. Most experiments will be done with isolate IPO323 of M. gramincola, the strain that was sequenced. Availability of a completely sequenced genome for M. graminicola provides a unique opportunity to analyze global gene expression to identify candidate genes for pathogenicity, sporulation, mating, light reception/regulation and other important biological processes. For some host-pathogen interactions isolates T48 from Indiana and isolate Pasco from Australia may be used. Isolate T48 is avirulent on all resistance sources tested so far but gives good infection on susceptible controls. It was used to map genes Stb1, Stb4 and Stb8. The Pasco isolate was used to map resistance genes Stb2 and Stb3 and can be used as a backup in case of problems with one of the other isolates.