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First published online November 18, 2005; 10.1104/pp.105.070433 Plant Physiology 139:1927-1934 (2005) © 2005 American Society of Plant Biologists Premature Leaf Senescence Modulated by the Arabidopsis PHYTOALEXIN DEFICIENT4 Gene Is Associated with Defense against the Phloem-Feeding Green Peach Aphid1,[W]Division of Biology and the Molecular Cellular and Developmental Biology Program (V.P., C.K., J.S.), and Department of Entomology (J.R.), Kansas State University, Manhattan, Kansas 66506–4901
Aphids, which are phloem-feeding insects, cause extensive loss of plant productivity and are vectors of plant viruses. Aphid feeding causes changes in resource allocation in the host, resulting in an increase in flow of nutrients to the insect-infested tissue. We hypothesized that leaf senescence, which is involved in the programmed degradation of cellular components and the export of nutrients out of the senescing leaf, could be utilized by plants to limit aphid growth. Using Arabidopsis (Arabidopsis thaliana) and green peach aphid (GPA; Myzus persicae Sulzer), we found that GPA feeding induced premature chlorosis and cell death, and increased the expression of SENESCENCE ASSOCIATED GENES (SAGs), all hallmarks of leaf senescence. Hypersenescence was accompanied by enhanced resistance against GPA in the Arabidopsis constitutive expresser of PR genes5 and suppressor of SA insensitivity2 mutant plants. In contrast, resistance against GPA was compromised in the phytoalexin deficient4 (pad4) mutant plant. The PAD4 gene, which is expressed at elevated level in response to GPA feeding, modulates the GPA feeding-induced leaf senescence. In comparison to the wild-type plant, GPA feeding-induced chlorophyll loss, cell death, and SAG expression were delayed in the pad4 mutant. Although PAD4 is associated with camalexin synthesis and salicylic acid (SA) signaling, camalexin and SA signaling are not important for restricting GPA growth; growth of GPA on the camalexin-biosynthesis mutant, pad3, and the SA deficient2 and NahG plants and the SA-signaling mutant, nonexpresser of PR genes1, were comparable to that on the wild-type plant. Our results suggest that PAD4 modulates the activation of senescence in the aphid-infested leaves, which contributes to basal resistance to GPA.
1 This work was supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture (agreement no. 2004–35301–14506); the National Science Foundation (grant no. MCB0416839); a Kansas State University Plant Biotechnology Center seed grant; the Kansas Idea Networks of Biomedical Research Excellence Grant (fellowship nos. K–INBRE and RR16475 to C.K.); and the Terry Johnson Cancer Center (fellowship to C.K.). This is Kansas Agricultural Experimental Station contribution 05–333–J. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jyoti Shah (shah{at}ksu.edu). [W] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070433. * Corresponding author; e-mail shah{at}ksu.edu; fax 785–532–6653. Received August 24, 2005; returned for revision October 7, 2005; accepted October 12, 2005. Related articles in Plant Physiol.:
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