D. S. Luthe,2
W. P. Williams,3 and
J. R. Wilkinson1
1Department of Biochemistry and Molecular Biology, Mississippi State University, Box 9650, Mississippi State, MS 39762, U.S.A.; 2Department of Crop and Soil Science, Pennsylvania State University, 116 ASI Building, University Park, PA 16802, U.S.A.; 3Corn Host Plant Research Laboratory, United States Department of Agriculture--Agricultural Research Service, Mississippi State University, Box 9555, Mississippi State, MS 39762, U.S.A.
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Accepted 9 August 2009.
In plants, ethylene and jasmonate control the defense responses to multiple stressors, including insect predation. Among the defense proteins known to be regulated by ethylene is maize insect resistance 1-cysteine protease (Mir1-CP). This protein is constitutively expressed in the insect-resistant maize (Zea mays) genotype Mp708; however, its abundance significantly increases during fall armyworm (Spodoptera frugiperda) herbivory. Within 1 h of herbivory by fall armyworm, Mir1-CP accumulates at the feeding site and continues to increase in abundance until 24 h without any increase in its transcript (mir1) levels. To resolve this discrepancy and elucidate the role of ethylene and jasmonate in the signaling of Mir1-CP expression, the effects of phytohormone biosynthesis and perception inhibitors on Mir1-CP expression were tested. Immunoblot analysis of Mir1-CP accumulation and quantitative reverse-transcriptase polymerase chain reaction examination of mir1 levels in these treated plants demonstrate that Mir1-CP accumulation is regulated by both transcript abundance and protein expression levels. The results also suggest that jasmonate functions upstream of ethylene in the 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.
© 2009 The American Phytopathological Society