Caterpillar attack triggers accumulation of the toxic maize protein RIP2

Abstract

SummarySome plant-derived anti-herbivore defensive proteins are induced by insect feeding, resist digestion in the caterpillar gut and are eliminated in the frass. We have identified several maize proteins in fall armyworm (Spodoptera frugiperda) frass that potentially play a role in herbivore defense. Furthermore, the toxicity of one of these proteins, ribosome-inactivating protein 2 (RIP2), was assessed and factors regulating its accumulation were determined.To understand factors regulating RIP2 protein accumulation, maize (Zea mays) plants were infested with fall armyworm larvae or treated with exogenous hormones. The toxicity of recombinant RIP2 protein against fall armyworm was tested.The results show that RIP2 protein is synthesized as an inactive proenzyme that can be processed in the caterpillar gut. Also, caterpillar feeding, but not mechanical wounding, induced foliar RIP2 protein accumulation. Quantitative real-time PCR indicated that RIP2 transcripts were rapidly induced (1 h) and immunoblot analysis indicated that RIP2 protein accumulated soon after attack and was present in the leaf for up to 4 d after caterpillar removal. Several phytohormones, including methyl jasmonate, ethylene, and abscisic acid, regulated RIP2 protein expression. Furthermore, bioassays of purified recombinant RIP2 protein against fall armyworm significantly retarded caterpillar growth.We conclude that the toxic protein RIP2 is induced by caterpillar feeding and is one of a potential suite of proteins that defend maize against chewing herbivores.

Turnabout Is Fair Play: Herbivory-Induced Plant Chitinases Excreted in Fall Armyworm Frass Suppress Herbivore Defenses in Maize

“…We used 18 biological replicates for each treatment, each of which was fed to 18 naïve FAW caterpillars for 3 d. Caterpillar mass was measured at the beginning and the end of the bioassay and used to calculate relative growth rates as described earlier (Hoffmann and Poorter, 2002;Mohan et al, 2008). Caterpillar feeding on plants is associated with the deposition of insect oral secretions and saliva, which can trigger herbivore-induced defenses in plants (Louis et al, 2013;Chuang et al, 2014a;Acevedo et al, 2015). To understand the effect of maize chitinases Pr4 and Endochitinase A on such plant defenses triggered by caterpillar herbivory, we fed fifth instar FAW larvae in inverted clip cages for 3 h as described in our previous study .…”

Ethylene Contributes to maize insect resistance1-Mediated Maize Defense against the Phloem Sap-Sucking Corn Leaf Aphid

“…In maize, it is known that caterpillar feeding increases JA levels both locally and systemically, which results in the activation of a suite of herbivore defenserelated genes including genes encoding enzymes in the JA biosynthetic pathway (Erb et al, 2009a;Shivaji et al, 2010). Furthermore, downstream genes that encode direct defense proteins such as proteinase inhibitor, chitinase, and Ribosome-Inactivating Protein2 are induced by caterpillar feeding (Shivaji et al, 2010;Chuang et al, 2014). Previous studies have shown that Mir1-CP accumulation in maize upon caterpillar feeding is dependent on both JA and ET pathways (Harfouche et al, 2006;Ankala et al, 2009).…”

Extensive Evolution of Cereal Ribosome-Inactivating Proteins Translates into Unique Structural Features, Activation Mechanisms, and Physiological Roles

“…Since the proRIP2 is not specifically expressed in seed tissue as is the case with proRIP1, the question remains whether activation in vivo is caused by exposure to endogenous proteases (as shown for proRIP1 during germination) or by exposure to proteases introduced by invading pests or pathogens [67]. Chuang et al [69] reported that proRIP2 can be processed in the midgut of fall armyworm into the active form.…”