Location: Hard Winter Wheat Genetics Research2011 Annual Report
1a. Objectives (from AD-416)
The objective of this research is to increase understanding of the molecular basis of host resistance and insect virulence in the wheat/Hessian fly system. The long-term goal is to develop strategies for durable resistance to this important insect pest.
1b. Approach (from AD-416)
The molecular basis of host resistance will be approached by cloning and characterizing a wheat resistance gene for Hessian fly known as Hdic from Triticum turgidum subsp. dicoccum. This resistance gene resides in a region of wheat chromosome 1A that contains at least 14 other resistance genes for Hessian fly. Candidate genes will be identified by fine mapping and sequencing of BAC contigs. Candidate genes will be tested initially by gene silencing using RNA interference. A cosmid library from the donor of Hdic will be constructed to isolate the resistance allele. Expression vectors will be constructed for the candidate gene and tested for ability to confer resistance to Hessian fly. The molecular basis of Hessian fly virulence/avirulence will be approached by determining the functions of secreted salivary gland proteins (SSGP) of Hessian fly in virulence or avirulence to wheat. Differential gene expression of SSGPs will be tested in different biotypes of Hessian fly using a custom-designed microarray. Candidate genes for virulence or avirulence effectors will be identified. Candidate genes will be tested by gene silencing using RNA interference.
3. Progress Report
We have cloned and characterized the Hessian fly resistance gene Hdic from wheat. Interestingly, the gene has homology to typical disease resistance genes. A manuscript is in preparation. We analyzed bacteria associated with Hessian fly at different developmental stages. Diverse bacteria were found in Hessian fly larvae, pupae, and adults. Most of the bacteria were transferred to the next generation through eggs. Removal of bacteria from the insect through antibiotics resulted in high mortality of Hessian fly larvae, indicating that symbiotic bacteria were essential for the insect to survive on wheat seedlings. Similar bacteria were also found in Hessian fly-infested wheat, suggesting that Hessian fly larvae transmit bacteria into plant tissue, and that these transmitted bacteria may play a role in the wheat-Hessian fly interaction. This research provides a foundation for future research on the role of bacteria in Hessian fly biology and virulence. Phytohormones were investigated for their possible role in parasitism of the Hessian fly on wheat. Salicylic acid and 12-oxo-phytodienoic acid were increased in both a resistant wheat variety and rice, which is a non-host. This suggests that phytohormones may be important components of the defense response. This research provides a foundation for future work on the role of phytohormones and fatty acids in the defense response against Hessian fly. Small interfering RNA (siRNA) has recently been found to play an important role in gene expression in eukaryotic organisms. Work was initiated on siRNA species in Hessian fly, and their potential roles in wheat/Hessian fly interactions. Progress on this agreement is monitored by regularly discussing program goals, approaches, and results (teleconference, email) and by reviewing annual accomplishments reports.