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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR MECHANISMS OF WHEAT RESISTANCE TO THE HESSIAN FLY
2013 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:

Hessian fly is a major insect pest of wheat. The insect is mainly controlled through host plant resistance. Therefore, understanding the mechanisms of wheat defense against Hessian fly may provide useful information to improve wheat resistance to Hessian fly. One potential target for plant defense against insects is the digestive enzymes, particularly proteases, in the insect gut. This research took advantage of the availability of the Hessian fly genome sequence and systematically analyzed the composition and expression of all digestive proteases in the Hessian fly larval gut. Major putative digestive trypsins, chymotrypsins, and cysteine proteases were identified and their expression profiles among tissues and different developmental stages were determined. The study should provide a foundation for future research for utilization of plant protease inhibitors for management of this insect pest.

Plant parasites, including many insects, manipulate plants in order to utilize the host resources. Here, we show that the Mayetiola destructor susceptibility gene-1 (Mds-1) of wheat encodes a small heat-shock protein and is a major susceptibility gene for infestation of wheat by the gall midge M. destructor, commonly known as the Hessian fly. Transcription of Mds-1 increased upon insect infestation. Silencing of Mds-1 transcript levels by RNA interference conferred immunity to all Hessian fly biotypes on normally susceptible wheat genotypes. Over-expression or induction by heat shock of Mds-1 suppressed resistance mediated by the resistance gene H13. Mds-1-silenced plants were also found to be resistant to the powdery mildew fungus, and Mds-1 expression was up-regulated during the fungal infection of normal wheat plants, suggesting that Hessian fly and powdery mildew exploit a common stress response pathway for parasitism. Modification of susceptibility genes may provide a potentially broad and durable source of resistance to Hessian fly and powdery mildew.


Last Modified: 12/20/2014
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