Plant defense production

The morphology of AM fungal structures developing outside and inside the root is conserved even in the rhizosphere of transgenic plants, where accumulation of antifungal plant defense products—such as lytic enzymes (e.g., chi-... 

In the natural world, carotenoid oxidation products are important mediators presenting different properties. Volatile carotenoid-derived compounds such as noriso-prenoids are well known for their aroma properties. Examples include the cyclic norisoprenoid P-ionone and the non-cyclic pseudoionone or Neral. Carotenoid oxidation products are also important bioactive mediators for plant development, the best-known example being abscisic acid. Apo-carotenoids act as visual and volatile signals to attract pollination and seed dispersal agents in the same way as carotenoids do, but they are also plant defense factors and signaling molecules for the regulation of plant architecture. 

Products released by the action of PL have previously been reported to act as elicitors of plant defense reactions (24,25,26,27). Accordingly, the transgenic plants described in this report provides an excellent mutant collection for the study of factors conferring resistance against Envinia carotovora bacteria. 

Saponins are glycosylated secondary metabolites that are widely distributed in the Plant Kingdom.3,4 They are a diverse and chemically complex family of compounds that can be divided into three major groups depending on the structure of the aglycone, which may be a steroid, a steroidal alkaloid, or a triterpenoid. These molecules have been proposed to contribute to plant defense.3 6 Saponins are also exploited as drugs and medicines and for a variety of other purposes.4 Despite the considerable commercial interest in this important group of natural products, little is known about their biosynthesis. This is due in part to the complexity of the molecules, and also to the lack of pathway intermediates for biochemical studies. 

In contrast, certain pathogens influence ethylene production involved in plant defense for their own benefit. Several of them are able to upregulate ethylene synthesis in plants as shown, for example, in virus- or bacteria-infected tobacco and citrus, respectively. ... 

PKSs are characterized by their ability to catalyze the formation of polyketide chains from the sequential condensation of acetate units from malonate thioesters. In plants they produce a range of natural products with varied in vivo and pharmacological properties. PKSs of particular note include acridone synthase, bibenzyl synthase, 2-pyrone synthase, and stilbene synthase (STS). STS forms resveratrol, a plant defense compound of much interest with regard to human health. STS shares high sequence identity with CHS, and is considered to have evolved from CHS more than once. ° Knowledge of the molecular structure of the CHS-like enzymes has allowed direct engineering of CHS and STS to alter their catalytic activities, including the number of condensations carried out (reviewed in Refs. 46, 51, 52). These reviews also present extensive, and superbly illustrated, discussions of CHS enzyme structure and reaction mechanism. 

Modification of isoflavonoid biosynthesis may have a wide range of applications for improving not only plant defense characters but also the health benefits of food for humans. With the exception of IFD (which may not be required in vivo), cDNA clones are available for all of the enzymes needed for the production of the isoflavonoid vestitone. Furthermore, as VR cDNAs have been cloned, only clones for the DMID are lacking for the biosynthetic branch of the antifungal pterocarpans. To date, experiments have focused on 2HIS, but there has also been success using IFR, I2 H, and I70MT. 

Higher plant allelochemical production of a compound that produces anomalous proteins while scrupulously avoiding diminution in the formation of these aberrant macromolecules certainly represents a subtly deceitful and highly effective form of chemical defense. 

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