Location: Wheat, Sorghum and Forage ResearchTitle: 12-Oxo-phytodienoic acid acts as a regulator of maize defense against corn leaf aphid
|VARSANI, SURESH - University Of Nebraska|
|ZHOU, SHAOQUN - Cornell University - New York|
|KOCH, KYLE - University Of Nebraska|
|Williams, William - Paul|
|HENG-MOSS, TIFFANY - University Of Nebraska|
|LUTHE, DAWN - Pennsylvania State University|
|JANDER, GEARG - Cornell University - New York|
|LOUIS, JOE - University Of Nebraska|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2019
Publication Date: 4/1/2019
Citation: Varsani, S., Zhou, S., Koch, K.G., Williams, W.P., Heng-Moss, T., Sarath, G., Luthe, D., Jander, G., Louis, J. 2019. 12-Oxo-phytodienoic acid acts as a regulator of maize defense against corn leaf aphid. Plant Physiology. 179:1402-1415. https://doi.org/10.1104/pp.18.01472.
Interpretive Summary: Maize plants are often attacked by corn leaf aphids. These aphids suck plant nutrients and can inject viral pathogens during feeding on maize leaves. As a result of aphid herbivory, maize plants can become stunted and corn yields can be compromised. However, maize plants resistant to corn leaf aphids have been bred. Here the physiological mechanisms underlying plant resistance to the corn leaf aphid were investigated using the resistant line Mp708. Aphid feeding on Mp708 plants led to the induction of several interrelated plant defensive mechanisms. A key finding of this work was that a plant compound OPDA, was shown to be a signaling molecule that induced plant defenses. Previously it had been assumed that OPDA effected its action as a toxin towards aphids. These findings suggest that further improvement in maize plant resistance could be possible by breeding plants that contain greater levels of OPDA in the absence of any aphids.
Technical Abstract: The corn leaf aphid (CLA; Rhopalosiphum maidis) is a phloem sap-sucking insect that attacks many cereal crops, including maize (Zea mays). We previously showed that the maize inbred line Mp708, which was developed by classical plant breeding, provides enhanced resistance to CLA. Here, using electrophysiological monitoring of aphid feeding behavior, we demonstrate that Mp708 provides phloem-mediated resistance to CLA. Furthermore, feeding by CLA on Mp708 plants enhanced callose deposition, a potential defense mechanism utilized by plants to limit aphid feeding and subsequent colonization. In maize, benzoxazinoids (BX) or BX-derived metabolites contribute to enhanced callose deposition by providing heightened resistance to CLA. However, BX and BX-derived metabolites were not significantly altered in CLA-infested Mp708 plants, indicating BX-independent defense against CLA. Evidence presented here suggests that the constitutively higher levels of 12-oxo-phytodienoic acid (OPDA) in Mp708 plants contributed to enhanced callose accumulation and heightened CLA resistance. OPDA enhanced the expression of ethylene biosynthesis and receptor genes, and the synergistic interactions of OPDA and CLA feeding significantly induced the expression of the transcripts encoding Maize insect resistance1-Cysteine Protease, a key defensive protein against insect pests, in Mp708 plants. Furthermore, exogenous application of OPDA on maize jasmonic acid-deficient plants caused enhanced callose accumulation and heightened resistance to CLA, suggesting that the OPDA-mediated resistance to CLA is independent of the jasmonic acid pathway. We further demonstrate that the signaling function of OPDA, rather than a direct toxic effect, contributes to enhanced CLA resistance in Mp708.