title: Aboveground to belowground herbivore defense signaling in maize: a two-way street?
abstract: Insect pests that attempt to feed on the caterpillar-resistant maize genotype Mp708 encounter a potent, multipronged defense system that thwarts their invasion. First, these plants are on "constant alert" due to constitutively elevated levels of the phytohormone jasmonic acid that signals the plant to activate its defenses. The higher jasmonic acid levels trigger the expression of defense genes prior to herbivore attack so the plants are "primed" and respond with a faster and stronger defense. The second defense is the rapid accumulation of a toxic cysteine protease called Mir1-CP in the maize whorl in response to caterpillar feeding. When caterpillars ingest Mir1-CP, it damages the insect's midgut and retards their growth. In this article, we discuss a third possible defense strategy employed by Mp708. We have shown that foliar caterpillar feeding causes Mir1-CP and defense gene transcripts to accumulate in its roots. We propose that caterpillar feeding aboveground sends a signal belowground via the phloem that results in Mir1-CP accumulation in the roots. We also postulate that the roots serve as a reservoir of Mir1-CP that can be mobilized to the whorl in response to caterpillar assault.
authors.affiliation: Department of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA, USA. dsl14@psu.edu
authors.forename: Dawn S
authors.initials: DS
authors.lastname: Luthe
authors.forename: Torrence
authors.initials: T
authors.lastname: Gill
authors.forename: Lixue
authors.initials: L
authors.lastname: Zhu
authors.forename: Lorena
authors.initials: L
authors.lastname: Lopéz
authors.forename: Olga
authors.initials: O
authors.lastname: Pechanova
authors.forename: Renuka
authors.initials: R
authors.lastname: Shivaji
authors.forename: Arunkanth
authors.initials: A
authors.lastname: Ankala
authors.forename: W Paul
authors.initials: WP
authors.lastname: Williams
mesh_terms: D000818:Animals; D005247:Feeding Behavior / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D015151:Immunoblotting; D008954:Models, Biological; D009928:Organ Specificity; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D018411:Spodoptera / Q000502:physiology; D003313:Zea mays / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D012333:RNA, Messenger