|LOUIS, JOE - University Of Nebraska|
|BASU, SAUMIK - University Of Nebraska|
|VARSANI, SURESH - University Of Nebraska|
|CASTANO-DUQUE, LINA - Pennsylvania State University|
|JIANG, VICTORIA - Pennsylvania State University|
|FELTON, GARY - Pennsylvania State University|
|LUTHE, DAWN - Pennsylvania State University|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2015
Publication Date: 10/1/2015
Citation: Louis, J., Basu, S., Varsani, S., Castano-Duque, L., Jiang, V., Williams, W.P., Felton, G., Luthe, D. 2015. Ethylene contributes to mir1-mediated maize defense against the phloem-sap sucking insect Rhopalosiphum maidis. Plant Physiology. 169:313-324.
Interpretive Summary: The gene, mir1, is an endogenous defense-signaling component in maize that encodes a cysteine protease, mir 1. The gene was discovered in corn germplasm lines, Mp704 and Mp708, that were developed and released by USDA-ARS at Mississippi State as sources of resistance to southwestern corn borer and fall armyworm. It was previously reported that the synergistic combination of ethylene and jasmonic acid was required for this cysteine protease to defend against a group of chewing insect pests of corn including fall armyworm and southwestern corn borer. The current study suggests that mir 1-mediated resistance to con leaf aphid, a phloem-sap sucking insect pest, is independent of jasmonic acid, but regulated by the ethylene signaling pathway. Feeding by corn leaf aphid triggers the rapid accumulation of mir 1 in Mp708. Furthermore, Mp708 exhibited enhanced levels of resistance to corn leaf aphid. This indicates that germplasm lines developed as sources of resistance to southwestern corn borer and fall armyworm could be used in breeding for enhanced resistance to corn leaf aphid as well.
Technical Abstract: Signaling networks among multiple phytohormones fine-tune plant defense responses to insect herbivore attack. Previously, it was reported that the synergistic combination of ethylene (ET) and jasmonic acid (JA) was required for providing maize insect resistance1 (mir1), a key endogenous defense signaling component, that provided defense against chewing group of insect pests in maize (Zea mays L.). However, our current study suggests that mir1-mediated resistance to corn leaf aphid [CLA; Rhopalosiphum maidis (Fitch)], a phloem-sap sucking insect pest, is independent of JA, but regulated by ET signaling pathway. Feeding by CLA triggers the rapid accumulation of mir1 transcripts in the resistant maize genotype, Mp708. Furthermore, Mp708 provided elevated levels of antibiosis (limits aphid population) and antixenosis (deters aphid settling) mediated resistance to CLA, compared to B73 and Tx601 maize susceptible inbred lines. Synthetic diet aphid feeding trial bioassays with recombinant Mir1-CP demonstrates that Mir1-CP provides direct toxicity to CLA. Furthermore, foliar feeding by CLA rapidly sends defensive signal(s) to the roots that trigger belowground accumulation of the mir1, signifying a potential role of long-distance signaling in maize defense against the phloem-feeding insects. Collectively, our data indicate that ET regulated mir1 transcript accumulation, uncoupled from JA, contributed to heightened resistance to CLA in maize. In addition, our results underscore the significance of ET acting as a central node in regulating mir1 expression to different feeding guilds of insect herbivores.