Insect-induced gene expression at the core of volatile terpene release in Medicago truncatula.

The blends of induced volatiles released by higher plants in response to herbivory regularly contain terpenoids. The precursors of volatile terpenoids can be synthesized via two pathways, the mevalonate (MVA) and the methyl erythritol 4-phosphate (MEP) pathways localized in the cytosol and in plastids, respectively. Terpenes are important players in interactions between plants and herbivorous insects, by acting in both direct and indirect defenses.

Medicago truncatula (E)-beta-ocimene synthase is induced by insect herbivory with corresponding increases in emission of volatile ocimene.

Virtually all plants are able to recognize attack by herbivorous insects and release volatile organic compounds (VOC) in response. Terpenes are the most abundant and varied class of insect-induced VOC from plants. Four genes encoding putative terpene synthases (MtTps1, MtTps2, MtTps3 and MtTps4) were shown to accumulate in Medicago truncatula Gaertn.

Allantoate amidohydrolase transcript expression is independent of drought tolerance in soybean.

Drought is a limiting factor for N(2) fixation in soybean [Glycine max (L.) Merr.] thereby resulting in reduced biomass accumulation and yield.

The plastid protein THYLAKOID FORMATION1 and the plasma membrane G-protein GPA1 interact in a novel sugar-signaling mechanism in Arabidopsis.

Mutations in genes encoding components of the heterotrimeric G-protein complex were previously shown to confer altered sensitivity to increased levels of D-glucose. This suggests that G-protein coupling may be a novel sugar-signaling mechanism in Arabidopsis thaliana. THYLAKOID FORMATION1 (THF1) is here demonstrated in vivo as a Galpha interaction partner that functions downstream of the plasma membrane-delimited heterotrimeric G-protein (GPA1) in a D-glucose signaling pathway.

Caterpillar herbivory and salivary enzymes decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis.

In response to caterpillar herbivory, alfalfa and related plant species defend themselves through the induction of saponin and volatile terpenoid biosynthesis. Both these types of defensive compounds are derived from the metabolic intermediate, isopentenyl diphosphate (IPP). In plants, two distinct biosynthetic pathways can generate IPP; the cytosolic mevalonate pathway and the plastid-associated 2C-methyl erythritol 4-phosphate (MEP) pathway.

Medicago truncatula mutants demonstrate the role of plant calcium oxalate crystals as an effective defense against chewing insects.

Calcium oxalate is the most abundant insoluble mineral found in plants and its crystals have been reported in more than 200 plant families. In the barrel medic Medicago truncatula Gaertn., these crystals accumulate predominantly in a sheath surrounding secondary veins of leaves.

Lepidopteran herbivory and oral factors induce transcripts encoding novel terpene synthases in Medicago truncatula.

Terpenes are an important class of defense compounds that accumulate in plants after pathogen infection or arthropod injury. Sequences predicted to encode terpene synthases were selected from an expressed sequence tag (EST) database of Medicago truncatula. Four putative terpene synthase clones (MtTps1-MtTps4), originating from a chewing insect-damaged M.

Deletion of the chloroplast-localized Thylakoid formation1 gene product in Arabidopsis leads to deficient thylakoid formation and variegated leaves.

Development of thylakoid membranes depends upon the transport of membrane vesicles from the chloroplast inner envelope and subsequent fusion of vesicles within the interior of the plastid. The Arabidopsis (Arabidopsis thaliana) Thylakoid formation1 (Thf1) gene product is shown here to control an important step required for the normal organization of these vesicles into mature thylakoid stacks and ultimately for leaf development. The Arabidopsis Thf1 gene encodes an imported chloroplast protein, as shown by in vitro import and localization of a Thf1-green fluorescent protein fusion product in transgenic plants.

Phenylpropanoid compounds and disease resistance in transgenic tobacco with altered expression of L-phenylalanine ammonia-lyase.

Tobacco plants over-expressing L-phenylalanine ammonia-lyase (PAL(+)) produce high levels of chlorogenic acid (CGA) and exhibit markedly reduced susceptibility to infection with the fungal pathogen Cercospora nicotianae, although their resistance to tobacco mosaic virus (TMV) is unchanged. Levels of the signal molecule salicylic acid (SA) were similar in uninfected PAL(+) and control plants and also following TMV infection. In crosses of PAL(+) tobacco with tobacco harboring the bacterial NahG salicylate hydroxylase gene, progeny harboring both transgenes lost resistance to TMV, indicating that SA is critical for resistance to TMV and that increased production of phenylpropanoid compounds such as CGA cannot substitute for the reduction in SA levels.

Profiling the response of plants to herbivorous insects.

Microarray analysis has confirmed that many of the modifications of gene expression that occur in plants following attack by herbivorous insects can be accounted for by the effects of compounds (elicitors) released by chewing insects. Recent experiments have revealed coordinated up- and down-regulation of transcripts encoding proteins with related functions, suggesting that large-scale shifts in metabolism take place in insect-damaged plants.