Lieceng Zhu

Gene Expression of Different Wheat Genotypes During Attack by Virulent and Avirulent Hessian Fly (Mayetiola destructor) Larvae

Wheat and its relatives possess a number of resistance (R) genes specific for the Hessian fly (HF) [Mayetiola destructor (Say)]. HF populations overcome R gene resistance by evolving virulence. Virulent HF larvae manipulate the plant to produce a nutritionally enhanced feeding tissue and, probably, also suppress plant defense responses. Using two wheat R genes, H9 and H13, and three HF strains (biotypes) differing in virulence for H9 and H13, we conducted a genome-wide transcriptional analysis of gene expression during compatible interactions with virulent larvae and incompatible interactions with avirulent larvae. During both types of interactions, a large number of genes (>1,000) showed alterations in gene expression. Analysis of genes with known functions revealed that major targets for differential regulation were genes that encoded defense proteins or enzymes involved in the phenylpropanoid, cell wall, and lipid metabolism pathways. A combination of the enhancement of antibiosis defense, the evasion of nutrient metabolism induction, and the fortification and expansion of the cell wall are likely the collective mechanism for host-plant resistance observed during incompatible interactions. To overcome this resistance, virulent larvae appeared to suppress antibiosis defense while inducing nutrient metabolism, weakening cell wall, and inhibiting plant growth.

Hessian Fly (Mayetiola destructor) Attack Causes a Dramatic Shift in Carbon and Nitrogen Metabolism in Wheat

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.

Rapid Mobilization of Membrane Lipids in Wheat Leaf-Sheaths during Incompatible Interactions with Hessian Fly

Hessian fly (HF) is a biotrophic insect that interacts with wheat on a gene-for-gene basis. We profiled changes in membrane lipids in two isogenic wheat lines: a susceptible line and its backcrossed offspring containing the resistance gene H13. Our results revealed a 32 to 45% reduction in total concentrations of 129 lipid species in resistant plants during incompatible interactions within 24 h after HF attack. A smaller and delayed response was observed in susceptible plants during compatible interactions. Microarray and real-time polymerase chain reaction analyses of 168 lipid-metabolism-related transcripts revealed that the abundance of many of these transcripts increased rapidly in resistant plants after HF attack but did not change in susceptible plants. In association with the rapid mobilization of membrane lipids, the concentrations of some fatty acids and 12-oxo-phytodienoic acid (OPDA) increased specifically in resistant plants. Exogenous application of OPDA increased mortality of HF larvae significantly. Collectively, our data, along with previously published results, indicate that the lipids were mobilized through lipolysis, producing free fatty acids, which were likely further converted into oxylipins and other defense molecules. Our results suggest that rapid mobilization of membrane lipids constitutes an important step for wheat to defend against HF attack.

Differential Accumulation of Phytohormones in Wheat Seedlings Attacked by Avirulent and Virulent Hessian Fly (Diptera: Cecidomyiidae) Larvae

ABSTRACT We analyzed the accumulation of six phytohormones and phytohormone-related compounds in a wheat, Triticum aestivium L., genotype, ‘Molly’, after attacks by avirulent and virulent Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), larvae, respectively, and we examined the expression of genes in the jasmonic acid (JA) pathway by Northern blot analysis. Compared with uninfested plants, attacks by avirulent larvae resulted in increased accumulation of salicylic acid (SA) by 11.3- and 8.2-fold, 12-oxo-phytodienoic acid (OPDA) by 36.4-and 18.7-fold, 18:3 fatty acid by 4.5- and 2.2-fold, and 18:1 fatty acid by 1.8- and 1.9-fold at 24 and 72 h post-initial attack (hpia), respectively, but an 20% decrease in JA accumulation at 24 hpia at the attack site. Attacks by the virulent larvae did not affect the accumulation of SA, OPDA, and 18:3 and 18:1 fatty acids but dramatically increased the concentration of auxin (AUX) from undetectable in uninfested plants to 381.7 ng/g fresh weight at 24 hpia and 71.0 ng/g fresh weight at 72 hpia in infested plants. Transcript levels of genes encoding lipoxygenase 2, allene oxide synthase, and Arabidopsis storage protein 2 were increased after avirulent larval attacks but decreased after virulent larval attacks. Our results suggest that OPDA and SA may act together in wheat resistance to the Hessian fly, whereas AUX may play a role in the susceptibility of wheat plants. The increased OPDA accumulation after avirulent larval attacks was at least partially regulated through gene transcription.

Electrical Penetration Graph Analysis of the Feeding Behavior of Soybean Aphids on Soybean Cultivars with Antibiosis

ABSTRACT The soybean aphid, Aphis glycine Matsumura (Hemiptera: Aphididae), is a major pest of soybean. In the current study, we used the Electrical Penetration Graph technique to study feeding behavior of soybean aphids on antibiotic-resistant soybean lines KS1621, KS1613, and KS1642, and a susceptible soybean line, KS4202. We observed that soybean aphids spent significantly shorter periods of time in the sieve element phase but slightly more times in nonprobing phases in all three resistant lines than in the susceptible control. Our study suggests that resistance factors exist in the phloem of the resistant soybean lines, and that these lines may contain antixenosis in addition to antibiosis.

Categories of Resistance to Biotype I Greenbugs (Homoptera: Aphididae) in Wheat Lines Containing the Greenbug Resistance Genes Gbx and Gby

Abstract The greenbug, Schizaphis graminum (Rondani), is a major pest of wheat in North America, reducing U.S. wheat production by

Changes in Phytohormones and Fatty Acids in Wheat and Rice Seedlings in Response to Hessian Fly (Diptera: Cecidomyiidae) Infestation

60 to

Transient Heat Stress Compromises the Resistance of Wheat (Poales: Poaceae) Seedlings to Hessian Fly (Diptera: Cecidomyiidae) Infestation

100 million each year. Experiments were conducted to determine the categories of resistance to greenbug biotype I controlled by two different resistance genes in wheat germplasm lines ‘KS89WGRC4’, containing the Gbx gene, and ‘Sandos 4040’, containing the Gby gene. Antixenosis (non-preference), antibiosis (lowered greenbug intrinsic rate of increase) and tolerance (reduced plant tissue and chlorophyll loss) assays were conducted using plants of Sandos 4040, KS89WGRC4, ‘Jagger’ (susceptible control), ‘Largo’ (antibiosis control), and ‘TA1675’ (tolerance control). Neither Sandos 4040, KS89WGRC4 nor the controls exhibited antixenosis to greenbug biotype I. There was an antibiotic effect on the greenbugs confined to Sandos 4040 (rm = 0.122), that was no different than the rm of aphids on the resistant control, Largo (rm = 0.144). Antibiosis was not present in KS89WGRC4. Both Sandos 4040 and KS89WGRC4 exhibited tolerance to greenbug biotype I feeding damage, based on measurements of proportional dry plant tissue weight change and leaf chlorophyll loss. Sandos 4040 and KS89WGRC4 provide useful new sources of resistance to greenbugs for wheat breeding programs.

Exogenous Salicylic Acid Enhances the Resistance of Wheat Seedlings to Hessian Fly (Diptera: Cecidomyiidae) Infestation Under Heat Stress.

ABSTRACT Phytohormones and fatty acids (FAs) play important roles in plant resistance to insects and pathogens. In this study, we investigated the similarities and differences in the accumulations of phytohormones and FAs in the resistant wheat (Triticum aestivum L.) ‘Molly’ and the nonhost rice (Oryza sativa L.) ‘Niponbare’ in responses to Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), larval attacks. Using chemical ionization-gas-chromatography/mass spectrometry, we analyzed the concentrations of 13 phytohomones and FAs at the attack site of wheat and rice plants at 1, 6, 24, or 48 h after the initial attack. Hessian fly attack resulted in increases of salicylic acid (SA), 12-oxo-phytodienoic acid (OPDA), palmitic acid (FA16:0), but a decrease of abscisic acid in both wheat and rice plants. In addition, the accumulation of jasmonic acid (JA) increased, whereas the accumulation of cinnamic acid (CA) decreased in wheat plants, but no changes were observed in the accumulation of JA, and the accumulation of CA increased in rice plants after Hessian fly attack. However, the accumulations of benzoic acid, strearic acid (FA18:0), and oleic acid (FA18:1) increased in rice plants, but no changes were observed in wheat plants after Hessian fly attack. Hessian fly-induced changes were more rapid in wheat plants in comparison with those in rice plants. Our study suggests that SA and OPDA may be involved in resistance of wheat and rice plants to Hessian fly and that the R gene-mediated resistance responses are more rapid than nonhost resistance responses.

Impact of Transient Heat Stress on Polar Lipid Metabolism in Seedlings of Wheat Near-Isogenic Lines Contrasting in Resistance to Hessian Fly (Cecidomyiidae) Infestation

ABSTRACT Heat stress exerts a profound impact on the resistance of plants to parasites. In this research, we investigated the impact of an acute transient heat stress on the resistance of the wheat line ‘Molly,’ which contains the R gene H13, to an avirulent Hessian fly (Mayetiola destructor (Say)) population. We found that a significant portion of Molly seedlings stressed at 40°C for 6 h during or after the initial Hessian fly larval attack became susceptible to otherwise avirulent insects, whereas unstressed control plants remained 100% resistant. Specifically, 77.8,73.3,83.3, and 46.7% of plants heat stressed at 0,6,12, and 24 h, respectively, after the initial larval attack became susceptible. Biochemical analysis revealed that heat stress caused a transient decrease in 12-oxo-phytodienoic acid, but an increase in salicylic acid accumulation in Molly plants. The change in phytohormones after heat stress and Hessian fly infestation was not observed in ‘Newton,’ a near-isogenic but Hessian fly susceptible wheat line. Instead, heat stress caused a relatively prolonged reduction in palmitoleic acid. The role of phytohormones in heat-induced loss of wheat resistance was discussed.