Carbon and nitrogen (C/N) metabolism and allocation within the plant have important implications for plant-parasite interactions. Many plant parasites manipulate the host by inducing C/N changes that benefit their own survival and growth. Plant resistance can prevent this parasite manipulation. We used the wheat–Hessian fly (Mayetiola destructor) system to analyze C/N changes in plants during compatible and incompatible interactions. The Hessian fly is an insect but shares many features with plant pathogens, being sessile during feeding stages and having avirulence (Avr) genes that match plant resistance genes in gene-for-gene relationships. Many wheat genes involved in C/N metabolism were differentially regulated in plants during compatible and incompatible interactions. In plants during compatible interactions, the content of free carbon-containing compounds decreased 36%, whereas the content of free nitrogen-containing compounds increased 46%. This C/N shift was likely achieved through a coordinated regulation of genes in a number of central metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and amino-acid synthesis. Our data on plants during compatible interactions support recent findings that Hessian fly larvae create nutritive cells at feeding (attack) sites and manipulate host plants to enhance their own survival and growth. In plants during incompatible interactions, most of the metabolic genes examined were not affected or down-regulated.

Background: The Barley stripe mosaic virus (BSMV)-based vector has been developed and used for gene silencing in barley and wheat seedlings to assess gene functions in pathogen- or insect-resistance, but conditions for gene silencing in spikes and grains have not been evaluated. In this study, we explored the feasibility of using BSMV for gene silencing in wheat spikes or grains. Results: Apparent photobleaching on the spikes infected with BSMV:PDS at heading stage was observed after13 days post inoculation (dpi), and persisted until 30dpi, while the spikes inoculated with BSMV:00 remained green during the same period. Grains of BSMV:PDS infected spikes also exhibited photobleaching. Molecular analysis indicated that photobleached spikes or grains resulted from the reduction of endogenous PDS transcript abundances, suggesting that BSMV:PDS was able to induce PDS silencing in wheat spikes and grains. Inoculation onto wheat spikes from heading to flowering stage was optimal for efficient silencing of PDS in wheat spikes. Furthermore, we used the BSMV-based system to reduce the transcript level of 1Bx14, a gene encoding for High-molecular-weight glutenin subunit 1Bx14 (HMW-GS 1Bx14), by 97 % in the grains of the BSMV:1Bx14 infected spikes at 15dpi, compared with that in BSMV:00 infected spikes, and the reduction persisted until at least 25 dpi. The amount of the HMW-GS 1Bx14 was also detectably decreased. The percentage of glutenin macropolymeric proteins in total proteins was significantly reduced in the grains of 1Bx14-silenced plants as compared with that in the grains of BSMV:00 infected control plants, indicating that HMW-GS 1Bx14 is one of major components participating in the formation of glutenin macropolymers in wheat grains. Conclusion: This is one of the first reports of successful application of BSMV-based virus-induced-gene-silencing (VIGS) for gene knockdown in wheat spikes and grains and its application in functional analysis of the 1Bx14 gene. The established BSMV-VIGS system will be very useful in future research on functional analysis of genes contributing to grain quality and the metabolic networks in developing seeds of wheat.