Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

Phytoalexin synthesis: the biochemical analysis of the induction process

Abstract: The biochemical basis of defense mechanisms conferring disease resistance on plants is now under active investigation. Plant resistance mechanisms are effective at different levels in host-parasite interactions and include preformed physical and chemical defense barriers as well as defenses triggered by the invader (69). One inducible defense response is the synthesis of phytoalexins at the site of attempted infection. Phytoalexins have been defined as anti­ microbial compounds of low-molecular weight that both are synthesized by and accumulate in plants after the exposure of the plant to microorganisms (113). They show the range and structural complexity typical of higher-plant natural products and are predominantly phenylpropanoids, isoprenoids, and acetylenes (5). The discovery of phytoalexins in interactions between parasites and host plants has encouraged many investigators to believe that these compounds are critical factors in regulating the interactions. Although this chapter presents considerable evidence that supports this view, it also discusses other results that may indicate a more limited role for phytoalexins. One particularly interesting aspect of these compounds originates from the fact that, in many systems, phytoalexin synthesis is strongly enhanced not only upon challenge of plant tissues by parasites but also following treatment with substances called elicitors. Because of their suspected role in disease processes, the nature and activity of several elicitors are described. Suitable experimental systems of reduced complexity, e.g. plant-cell cultures and elicitors, as well

Oligosaccharins: structures and signal transduction.

Abstract: Oligosaccharins are complex carbohydrates that can function in plants as molecular signals that regulate growth, development, and survival in the environment [3]. Studies of plant-microorganism interactions yielded the first evidence that oligosaccharins could serve as biological signals. Much of this research focused on the synthesis and accumulation of antimicrobial phytoalexins in response to microbial attack. Phytoalexin synthesis and accumulation are observed not only after microbial infection, but also after treatment of plant tissue with cell-free extracts of microbial origin. The active components in these extracts are commonly referred to as ‘elicitors’. The term ‘elicitor’ was originally used to refer to molecules and other stimuli that induce the synthesis and accumulation of phytoalexins in plant cells [130], but is now commonly used for molecules that stimulate any plant defense mechanism [68, 70, 71, 104].

Phytoalexin-deficient mutants of Arabidopsis reveal that PAD4 encodes a regulatory factor and that four PAD genes contribute to downy mildew resistance.

Abstract: We are working to determine the role of the Arabidopsis phytoalexin, camalexin, in protecting the plant from pathogen attack by isolating phytoalexin-deficient (pad) mutants in the accession Columbia (Col-0) and examining their response to pathogens. Mutations in PAD1, PAD2, and PAD4 caused enhanced susceptibility to the bacterial pathogen Pseudomonas syringae pv. maculicola strain ES4326 (PsmES4326), while mutations in PAD3 or PAD5 did not. Camalexin was not detected in any of the double mutants pad1-1 pad2-1, pad1-1 pad3-1 or pad2-1 pad3-1. Growth of PsmES4326 in pad1-1 pad2-1 was greater than that in pad1-1 or pad2-1 plants, while growth in pad1-1 pad3-1 and pad2-1 pad3-1 plants was similar to that in pad1-1 and pad2-1 plants, respectively. The pad4-1 mutation caused reduced camalexin synthesis in response to PsmES4326 infection, but not in response to Cochliobolus carbonum infection, indicating that PAD4 has a regulatory function. PAD1, PAD2, PAD3 and PAD4 are all required for resistance to the eukaryotic biotroph Peronospora parasitica. The pad4-1 mutation caused the most dramatic change, exhibiting full susceptibility to four of six Col-incompatible parasite isolates. Interestingly, each combination of double mutants between pad1-1, pad2-1 and pad3-1 exhibited additive shifts to moderate or full susceptibility to most of the isolates.

Arabidopsis PAD3, a Gene Required for Camalexin Biosynthesis, Encodes a Putative Cytochrome P450 Monooxygenase

Abstract: Phytoalexins are low molecular weight antimicrobial compounds that are synthesized in response to pathogen attack. The phytoalexin camalexin, an indole derivative, is produced by Arabidopsis in response to infection with the bacterial pathogen Pseudomonas syringae. The phytoalexin deficient 3 (pad3) mutation, which causes a defect in camalexin production, has no effect on resistance to P. syringae but compromises resistance to the fungal pathogen Alternaria brassicicola. We have now isolated PAD3 by map-based cloning. The predicted PAD3 protein appears to be a cytochrome P450 monooxygenase, similar to those from maize that catalyze synthesis of the indole-derived secondary metabolite 2,4-dihydroxy-1, 4-benzoxazin-3-one. The expression of PAD3 is tightly correlated with camalexin synthesis and is regulated by PAD4 and PAD1. On the basis of these findings, we conclude that PAD3 almost certainly encodes an enzyme required for camalexin biosynthesis. Moreover, these results strongly support the idea that camalexin does not play a major role in plant resistance to P. syringae infection, although it is involved in resistance to a fungal pathogen.