Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2009
Publication Date: 10/1/2009
Citation: Ankala, A., Luthe, D.S., Williams, W.P., Wilkinson, J.R. 2009. Integration of Ethylene and Jasmonic Acid Signaling Pathways in the Expression of Novel Maize Defense Protein Mir1-CP. Molecular Plant-Microbe Interactions. 22:1555-1564.
Interpretive Summary: Fall armyworm is a major insect pest of corn in the southern USA. Growing corn hybrids with genetic resistance to this pest is a desirable method of reducing losses. USDA-ARS at Mississippi State, MS developed and released corn germplasm lines with resistance to fall armyworm, southwestern corn borer, and other Lepidoptera. A unique cysteine proteinase (Mir1-CP) was identified in these resistant germplasm lines. The protein is constitutively expressed at low levels in insect-resistant germplasm, but it increases abundance in a two stage defensive response to insect feeding. Knowledge of the expression of Mir1-CP as a defensive protein will enhance efforts to use the insect resistant germplasm in applied plant breeding programs to fall armyworm resistant corn hybrids. These hybrids will reduce insect damage and the need for chemical insecticides.
Technical Abstract: In plants, ethylene (ET) and jasmonate (JA) control the defense responses to multiple stressors, including insect predation. Among the defense proteins known to be regulated by ET, is maize insect resistance 1-cysteine protease (Mir1-CP). This protein is constitutively expressed in the insect resistant maize (Zea mays) genotype Mp708, but its abundance significantly increases during fall armyworm (FAW, Spodoptera frugiperda) herbivory. Within 1 h of herbivory by FAW, Mir1-CP accumulates at the feeding site and continues to increase in abundance even until 24 h without any increase in its transcript (mir1) levels. To explain this discrepancy and to elucidate the probable role of JA in the signaling of Mir1-CP expression, pharmacological approach involving treatment of plants with phytohormones (ET and JA) and their biosynthesis or perception inhibitors, was employed. Immunoblot analysis of Mir1-CP accumulation and qRT-PCR examination of mir1 levels in these treated plants demonstrate that Mir1-CP expression is both transcriptionally and post-transcriptionally regulated. We also report that JA functions upstream of ET in Mir1-CP expression pathway, allowing for both low level constitutive expression and a two stage defensive response; an immediate response involving Mir1-CP accumulation and a delayed response inducing mir1 transcript expression.