GENETIC ENHANCEMENT FOR RESISTANCE TO BIOTIC AND ABIOTIC STRESSES IN HARD WINTER WHEAT
Location: Hard Winter Wheat Genetics Research Unit
Title: Differential Accumulation of Phytohormones in Wheat Seedlings Attacked by Avirulent and Virulent Hessian Fly (Diptera: Cecidomyiidae) Larvae
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2009
Publication Date: February 1, 2010
Citation: Zhu, L., Liu, X., Chen, M. 2010. Differential Accumulation of Phytohormones in Wheat Seedlings Attacked by Avirulent and Virulent Hessian Fly (Diptera: Cecidomyiidae) Larvae. Journal of Economic Entomology. 103:178-185.
Interpretive Summary: Host plant resistance is the most effective and cost efficient means to control Hessian fly (Mayetiola destructor), a serious pest of wheat. However, the rapid development of new biotypes has made resistance in host plants short-lived, lasting for only 6-8 years for a specific resistance gene. A better understanding of plant resistance mechanisms is needed to develop more durable resistant wheat. This research investigated changes in concentrations of plant hormones in plants attacked by virulent and avirulent Hessian fly larvae. We found that salicylic acid (SA) and 12-oxo-phytodienoic acid (OPDA) were increased in plants attacked by avirulent larvae, indicating that these two hormones may play an important role in wheat resistance to Hessian fly. On the other hand, the plant hormone auxin increased dramatically in plants attacked by virulent larvae, suggesting that Hessian fly larvae may manipulate host plants to their advantage via auxin. This research provided a foundation for future research that will lead to a better understanding of the roles of plant hormones in wheat-Hessian fly interactions, and may eventually lead to practical applications.
We analyzed the accumulation of six phytohormones and phytohormone-related compounds in a wheat [Triticum aestivium (L.)] genotype ‘Molly’ following attacks by avirulent and virulent Hessian fly [Mayetiola destructor (Say)] larvae, respectively, and examined the expression of genes in the jasmonic acid (JA) pathway by Northern blot analysis. Attack by avirulent insects 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- and1.9- fold at 24- and 72-hours post initial attack (hpia), respectively, but a 20% decrease in JA accumulation at 24-hpia. Attack by virulent insects did not affect the accumulation of SA, OPDA, 18:3 and 18:1 fatty acids, but resulted in a dramatic increase in auxin (AUX), with concentration from undetectable in uninfected plants to 381.7 ng/g fresh weight in 24-hpia and 71.0 ng/g fresh weight in 72-hpia in infested plants. Transcript levels of the genes encoding lipoxygenase 2 (LOX2), allene oxide synthase (AOS), and Arabidopsis storage protein 2 (AtVSP2) increased following avirulent larval attack, but decreased following virulent larval attack. 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 resulting from avirulent larval attack was at least partially regulated through gene transcription.