Publikationen - Molekulare Signalverarbeitung

Jasmonates are essential engineers of plant defense responses against many pests, including herbivorous insects. Herbivory induces the production of jasmonic acid (JA) and its bioactive conjugate jasmonoyl-l-isoleucine (JA-Ile), which then triggers a large transcriptional reprogramming to promote plant acclimation. The contribution of the JA pathway, including its components and regulators, to defense responses against insect herbivory can be evaluated by conducting bioassays with a wide range of host plants and insect pests. Here, we describe a detailed and reproducible protocol for testing feeding behavior of the generalist herbivore Spodoptera littoralis on the model plant Arabidopsis thaliana and hence infer the contribution of JA-mediated plant defense responses to a chewing insect.

Chrysanthemum chlorotic mottle viroid (CChMVd) (398–401 nt) belongs to genus Pelamoviroid, family Avsunviroidae and, like other members of this family, replicates in plastids through a rolling-circle mechanism involving hammerhead ribozymes. CChMVd RNA adopts a branched conformation stabilized by a kissing-loop interaction, resembling peach latent mosaic viroid in this respect. Chrysanthemum is the only natural and experimental host for CChMVd, which in the most sensitive varieties induces leaf mottling and chlorosis, delay in flowering, and dwarfing. The viroid has been found in major chrysanthemum growing areas including Europe and Asia. There are natural variants in which the change (UUUC→GAAA) mapping at a tetraloop in the CChMVd branched conformation is sufficient to change the symptomatic phenotype into a nonsymptomatic one without altering the viroid titer. Preinfection with nonsymptomatic variants prevents challenge inoculation with symptomatic ones. Moreover, experimental coinoculation with symptomatic and nonsymptomatic CChMVd variants results in symptomless phenotypes only when the latter is in vast excess, thus indicating its lower fitness.

This chapter focuses on Ophioviridae family whose sole member genus is Ophiovirus. The member species of the genus include Citrus psorosis virus (CPsV), Freesia sneak virus(FreSV), Lettuce ring necrosis virus (LRNV), and Mirafiori lettuce big-vein virus (MiLBVV).The single stranded negative/possibly ambisense RNA genome is divided into 3–4 segments, each of which is encapsidated in a single coat protein (43–50 kDa) forming filamentous virions of about 3 nm in diameter, in shape of kinked or probably internally coiled circles of at least two different contour lengths. Ophioviruses can be mechanically transmitted to a limited range of test plants, inducing local lesions and systemic mottle. The natural hosts of CPsV, ranunculus white mottle virus (RWMV), MiLBVV, and LRNV are dicotyledonous plants of widely differing taxonomy. CPsV has a wide geographical distribution in citrus in the Americas, in the Mediterranean and in New Zealand. FreSV has been reported in two species of the family Ranunculacae from Northern Italy, and in lettuce in France and Germany. Tulip mild mottle mosaic virus (TMMMV) has been reported in tulips in Japan. LRNV is closely associated with lettuce ring necrosis disease in The Netherlands, Belgium, and France, and FreSV has been reported in Europe, Africa, North America and New Zealand.

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The etiolated germination process of oilseed plants is characterized by the mobilization of storage lipids which serve as a major carbon source for the seedlings growth. During this stage the lipid storing organelles, the lipid bodies, are degraded and a new set of proteins, including a specific form of lipoxygenase (LOX), is detectable at their membranes in different plants [1,2]. LOXs are widely distributed in plants and animals and catalyze the regio- and stereo-specific oxygenation of polyunsaturated fatty acids [3]. The enzymatic transformations of the resulting fatty acid hydroperoxides have been extensively studied [4]. Three well characterized enzymes, a lyase, an allene oxide synthase, and a peroxygenase, were shown to degrade hydroperoxides into compounds of physiological importance, such as odors, oxylipins, and jasmonates. We have recently reported a new LOX reaction in plants where a specific LOX, the lipid body LOX, metabolizes esterified fatty acids. This reaction resulted in the formation of 13(S)-hydroxy-linoleic acid (13-HODE) and lead us to propose an additional branch of the LOX pathway: the reductase pathway. Besides a specific LOX form we suggest two additional enzyme activities, a lipid hydroperoxide reductase and a lipid hydroxide-specific lipase which lead to the formation of 13-HODE. 13-HODE might be the endogenous substrate for β-oxidation in the glyoxysomes during germination of oilseeds containing high amounts of polyunsaturated fatty acids.