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A Functional Genomic Approach to Identify
Genes Modulating
Plant Defense Responses to Arthropod Challenge
This summary describes the results of functional genomics studies conducted
to identify plant genes activated in response to attack by an aphid,
Diuraphis noxia.
During the past 10 years,
my group has characterized a gene cluster in common wheat responsible for
imparting resistance to an aphid herbivore, Diuraphis noxia (Kurdjumov) and
has made progress in determining the factors affecting the expression of one
gene - Dnx - in this cluster (Liu et al. 2001, 2002, 2005). More recently,
we have determined several components of the differential expression of Dnx
in D. noxia - resistant wheat plants using suppressive subtraction
hybridization and microarray hybridization (Boyko et al. 2006, Smith et al.
unpubl.).
Over 40 classes of sequences are expressed in D. noxia resistant- and
susceptible plants at 48 hr after D. noxia infestation. The derived Dnx
subtracted cDNA library includes sequences similar to Pto and Pti1 - genes
involved in gene-for-gene recognition of and resistance to bacterial speck
disease in tomato, and suggests that similar gene-for-gene events may induce
defense responses and D. noxia resistance in Dnx wheat. Defense signaling in
Dnx plants is represented by sequences putatively involved in the production
of sterols, jasmonates (JA), Ca2+(ROS), abcisic (ABA) and gibberelic (GA)
acids. Reductions in populations of D. noxia fed Dnx plants is likely
related to the expression of sequences involved in the production of
defensive allelochemicals and exocytosis. In experiments conducted with the
Affymetrix 55,000 transcript wheat array, Dnx plants respond vigorously to
D. noxia feeding even earlier (24 hr post-infestation), activating the
expression of ~5 X more genes than in susceptible Dn0 plants. Over 100
classes of expressed plant sequences are involved in ABA-, ET-, GA-, JA-,
ROS- and salicyate- mediated signaling; as well as resistance to tissue
damage and water loss.
We are interested in the effects of temperature on plant defense response to
D. noxia, because this aphid can withstand high temperature environments and
because virulence has been linked to temperature effects. Our results to
date demonstrate the temperature-based modulation of Dnx. Of the 40+ genes
expressed in Dnx and Dn0 plants at 48 hr after D. noxia infestation at 27oC,
those in infested Dnx plants are up-regulated at from 2 - 9 fold greater
levels than the same sequences in un-infested Dnx plants or in infested Dn0
plants. At 38oC, some of the defense response signaling and cell protection
genes in Dnx plants are slightly down-regulated, but a putative vacuolar
proton-ATPase important in plant signaling and environmental stress
tolerance (Kluge et al. 2003) remains highly (17 x) up-regulated, compared
to uninfested Dnx plants. Interestingly, Dn0 plants up-regulate many of the
D. noxia response-related sequences at 380C, canceling many of the
differences between resistant and susceptible plants at 270C. Nevertheless,
the phenotypic resistance of Dnx plants persists at 380C, suggesting the
existence of alternative D. noxia defense pathways in Dnx plants. Presently,
we are using phytohormone profiling to identify key compounds involved in
the temperature responses of resistant and susceptible plants.
We are also continuing to study the interactions of genes in wheat plants
expressed in response to new virulent aphid biotypes, 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.
Kluge, C., J. Lahr, M. Hanitzsch, S. Bolte, D. Golldack, and K. J. Dietz.
(2003) New insight into the structure and regulation of the plant vacuolar
H+-ATPase. J. Bioenerg. Biomembr. 35: 377-388.
Liu, X. M., C. M. Smith, B. S. Gill, and V. Tolmay. (2001) Microsatellite
markers linked to six Russian wheat aphid resistance genes in wheat. Theor.
Appl. Genet. 102:504-510.
Liu, X. M., C. M. Smith, and B. S. Gill. (2002) Mapping of microsatellite
markers linked to the Dn4 and Dn6 genes expressing Russian wheat aphid
resistance in wheat. Theor. Appl. Genet. 104:1042-1048.
Liu, X. M., C. M. Smith and B. S. Gill. (2005) Allelic relationships among
Russian wheat aphid resistance genes. Crop Sci. 45:2273-2280.
Publications
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.
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.
Smith, C. M., T. Belay, C. Stauffer, P. Stary, I. Kubeckova, and S. Starkey
(2004) Identification of Russian wheat aphid (Homoptera: Aphididae) biotypes
virulent to the Dn4 resistance gene. 97:1112 - 1117.
Smith, C. M. and E. V. Boyko. (2006) Plant Expression of Defense Response
and Resistance Genes Elicited by Aphid Feeding. Mini Review - Entomol. Exp.
Appl. (In press)
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., L. Zhu, C. Khajuria, J. Lewis, J. Meng, C. M. Smith, G. E.
Wilde and C. A. Baker. (2006) Categories and inheritance of resistance in
wheat Cereal Introduction 2401 to Russian wheat aphid (Homoptera: Aphididae)
biotypes 1 and 2. J. Econ. Entomol. 99: (In press).
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