Research
Gene Expression Interactions Between Wheat Plants and Virulent and Avirulent Aphid Biotypes
C. Michael Smith, Professor, Department of Entomology Kansas State University
Differential gene expression in interactions between Diuraphis noxia and its cereal plant hosts involves a coordinated, complex set of plant defense responses involving more than 180 known genes involved in cell membrane permeability; ROS; ABA, ET, JA, and SA signaling; pathogen defense; and the expression of genes resulting in both arthropod allelochemical and biophysical defense factors (Boyko et al. 2006, Smith et al. unpubl.) Defense-related gene expression significantly increases within 6 to 24 hours post infestation (hpi) in resistant plants but is delayed in susceptible plants until 48- to 96 hpi. Putative allelochemical resistance factors include feeding inhibitors, toxic proteins, and PDR ABC toxin transport proteins, indicating that Dnx defenses involve the movement of toxins into the phloem for ingestion by D. noxia. Biophysical defenses result from the up-regulation of more than 40 genes involved in plant biomass production or water loss response, supporting the contention that reduced tissue and water loss in resistant plants also function in D. noxia resistance. Quantitative differences of several defense-related phytohormones in resistant and susceptible foliage assessed via vapor phase extraction and CI-GC/MS analysis validate the gene expression results for methyl-SA, methyl-JA and trans OPDA (Lazzari et al. unpubl.)
Companion experiments involving the electronic monitoring of D. noxia feeding indicate that aphids locate leaf phloem in approximately the same amount of time on both resistant and susceptible plants, but that significantly more salivation and phloem ingestion occurs on susceptible plants than on resistant plants in the first 8 h of feeding (Ray-Chandler et al. unpubl.). Although aphids access phloem sap on both plants, they fail to maintain committed phloem ingestion on resistant plants. These results support the contention that resistance factors such as feeding inhibitors, antifeedants and toxins reside in the phloem sap of resistant plants.
To understand the differential expression transcriptome of D. noxia in response to plant resistance factors normalized gut cDNA libraries from D. noxia biotypes 1 and 2 fed on biotype 1 resistant, biotype 2 susceptible plants prepared and sequenced in an attempt to identify putative biotype-specific genes. Libraries of both biotypes contain numerous genes putatively encoding enzymes involved in digestion & detoxification, and library comparisons detected significant biotype differences in expression of different groups of trypsin- & chymotrypsin-like serine proteases (Ananthakrishnan et al. unpubl.). These results provide addition evidence of the involvement of allelochemical factors in D. noxia resistant plants.
Present studies involve the use of phytohormone (JA, SA, ABA, ET) profiling to identify key genes involved in plant response to D. noxiaherbivory, in order to contribute to the overall goals of the Ecological Genomics TE Institute.
References
Boyko, E. V., C. M. Smith, T. Vankatappa, J. Bruno, Y. Deng, S. R. Starkey, and D. Klaahsen. (2006) The molecular basis of plant gene expression during aphid invasion: wheat Pto- and Pti-like sequences modulate aphid-wheat interaction. J. Econ. Entomol. 99:1430-1445.
Publications
Enali, S., R. Anathakrishnan, T. Niide, L. Starkus, S. Starkey, and C. M. Smith. (200#) Comparisons of Wheat and Barley Resistance to Russian Wheat Aphid Biotype 2. Arthropod Plant. Interact. (Submitted).
Saker, M. M. , S. Adawy, and C. M. Smith. (2007) Entomological and genetic variation of cultivated barley (Hordeum vulgare) from Egypt.GAPP Arch. Phytopathol. Plant Protect. 40: (In Press) DOI: 10.1080/03235400600881612. First Published on 15 September, 2006.
Smith, C. M. and E. V. Boyko. (2007) Mini Review: The molecular bases of plant resistance and defense responses to aphid feeding: current status. Entomol. Exp. Appl. 122: 1-16.
Boyko, E. V., C. M. Smith, T. Vankatappa, J. Bruno, Y. Deng, S. R. Starkey, and D. Klaahsen. (2006) The molecular basis of plant gene expression during aphid invasion: wheat Pto- and Pti-like sequences modulate aphid-wheat interaction. J. Econ. Entomol. 99:1430-1445.
Smith, C. M., E. V. Boyko and S. Starkey. (2006) Differential Expression of Genes in Wheat, Tritiucum aestivum L. Controlling Resistance to the Russian Wheat Aphid, Diuraphis noxia (Mordvilko). IOBC wprs Bull. 28:11-20.
Voothuluru, P., J. Meng, C. Khajuria, J. Louis, L. Zhu, S Starkey, G. E. Wilde, C. A. Baker and C. M. Smith. (2006) Categories and inheritance of resistance to Russian wheat aphid (Homoptera: Aphididae) Biotype 2 in a selection from wheat cereal introduction 2401. J. Econ. Entomol. 99: 1854-1861.
Liu, X. M., C. M. Smith and B. S. Gill. (2005) Allelic relationships among Russian wheat aphid resistance genes. Crop Sci. 45:2273-2280.
Smith, C. M. (2005) Plant Resistance to Arthropods – Molecular and Conventional Approaches. Springer, Berlin. 423 pp.
