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BIOLOGICAL SCIENCES / PLANT BIOLOGY
Tomato MAPKs LeMPK1, LeMPK2, and LeMPK3 function in the systemin-mediated defense response against herbivorous insects
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Departments of *Biological Sciences and ¶Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208; and Department of Energy–Plant Research Laboratory, Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824
Edited by Clarence A. Ryan, Jr., Washington State University, Pullman, WA, and approved June 7, 2007 (received for review January 12, 2007)
Systemin is a wound-signaling peptide that mediates defenses of tomato plants against herbivorous insects. Perception of systemin by the membrane-bound receptor SR160 results in activation of MAPKs, synthesis of jasmonic acid (JA), and expression of defense genes. To test the function of MAPKs in the response to systemin, we used virus-induced gene silencing (VIGS) in plants that overexpress the systemin precursor prosystemin (35S::prosys plants). These transgenic plants accumulate high levels of defense proteins and exhibit increased resistance to herbivorous insects. Cosilencing of the MAPKs MPK1 and MPK2 reduced MPK1/2 kinase activity, JA biosynthesis, and expression of JA-dependent defense genes. Application of methyl-JA restored the full defense response. These data show that MPK1 and MPK2 are essential components of the systemin signaling pathway and most likely function upstream of JA biosynthesis. MPK1 and MPK2 are 95% identical at the amino acid level. Specific VIGS of only MPK1 or MPK2 resulted in the same reduction of defense gene expression as cosilencing of MPK1 and MPK2, indicating that gene dosage effects may be important for MPK signaling. In addition, VIGS of the closely related MPK3 also reduced systemin-induced defense responses. The function of MPK1/2 and orthologs in pathogen-induced defenses is well established. Here we show that cosilencing of MPK1 and MPK2 compromised prosystemin-mediated resistance to Manduca sexta (Lepidoptera) herbivory, demonstrating that MPK1 and MPK2 are also required for successful defenses against herbivorous insects.
jasmonic acid | plant–insect interactions | virus-induced gene silencing
Present address: Leibniz Institute of Plant Biochemistry, Department of Stress and Developmental Biology, D-06120 Halle (Saale), Germany.
Present address: San Luis Valley Research Center, Colorado State University, Center, CO 81125.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0700344104/DC1.
||To whom correspondence should be addressed. E-mail: johstrat{at}biol.sc.edu
© 2007 by The National Academy of Sciences of the USA
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