Defense by Pyrrolizidine Alkaloids: Developed by Plants and Recruited by Insects

Hartmann, Thomas; Ober, Dietrich

doi:10.1007/978-1-4020-8182-8_10

Cited by 30 publications

(26 citation statements)

References 89 publications

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“…PAs are part of the plant's defense against herbivores. They are composed of a necine base moiety that is esterified with one or more necic acid moieties (reviewed in Hartmann and Ober 2008;Ober 2003). Like the DHS, HSS transfers an aminobutyl moiety of spermidine in a NAD ?…”

Section: Introductionmentioning

confidence: 99%

Homospermidine in transgenic tobacco results in considerably reduced spermidine levels but is not converted to pyrrolizidine alkaloid precursors

Abdelhady

Beuerle²,

Ober

2009

Plant Mol Biol

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Homospermidine synthase is the first specific enzyme in the biosynthesis of pyrrolizidine alkaloids. Whereas the substrates putrescine and spermidine are part of the highly dynamic polyamine pool of plants, the product homospermidine is incorporated exclusively into the necine base moiety of pyrrolizidine alkaloids. Recently, the gene encoding homospermidine synthase has been shown to have been recruited several times independently during angiosperm evolution by the duplication of the gene encoding deoxyhypusine synthase. To test whether high levels of homospermidine suffice for conversion, at least in traces, to precursors of pyrrolizidine alkaloids, transgenic tobacco plants were generated expressing homospermidine synthase. Analyses of the polyamine content revealed that, in the transgenic plants, about 80% of spermidine was replaced by homospermidine without any conspicuous modifications of the phenotype. Tracer-feeding experiments and gas chromatographic analyses suggested that these high levels of homospermidine were not sufficient to explain the formation of alkaloid precursors. These results are discussed with respect to current models of pathway evolution.

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Section: Introductionmentioning

confidence: 99%

Homospermidine in transgenic tobacco results in considerably reduced spermidine levels but is not converted to pyrrolizidine alkaloid precursors

Abdelhady

Beuerle²,

Ober

2009

Plant Mol Biol

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“…Such a scenario has been demonstrated for HSS evolution in the Asteraceae, in which independent duplications of the dhs gene and subsequent recruitment of the duplicated gene for PA biosynthesis have been found within the tribes Senecioneae and Eupatorieae. Both tribes are characterized by different types of PAs, the senecionine type and the lycopsamine type, respectively (Reimann et al, 2004;Hartmann and Ober, 2008). The diverse PAs of the Convolvulaceae include (1) the ipangulines and minalobines, which are characterized by 1,2-saturated necine bases forming monoand diesters with aromatic and aliphatic necic acids ( Figure 1A) detected in Ipomoea species of the section Mina (Jenett-Siems et al, 1993, 1998; (2) PAs of the triangularine type (i.e., necine bases esterified with mainly aliphatic C 5 -necic acids) ( Figure 1B), detected in Ipomoea meyeri, a species of the section Pharbitis series Pharbitis (Tofern, 1999;Eich, 2008); (3) PAs of the lycopsamine type found within Merremia quinquefolia ( Figure 1C), the only species within this family in which 1,2-unsaturated PAs have been identified (Mann, 1997;Eich, 2008); and (4) the lolines ( Figure 1D), found in Argyreia mollis .…”

Section: Introductionmentioning

confidence: 99%

Evolution of Homospermidine Synthase in the Convolvulaceae: A Story of Gene Duplication, Gene Loss, and Periods of Various Selection Pressures

2013

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Homospermidine synthase (HSS), the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, is known to have its origin in the duplication of a gene encoding deoxyhypusine synthase. To study the processes that followed this gene duplication event and gave rise to HSS, we identified sequences encoding HSS and deoxyhypusine synthase from various species of the Convolvulaceae. We show that HSS evolved only once in this lineage. This duplication event was followed by several losses of a functional gene copy attributable to gene loss or pseudogenization. Statistical analyses of sequence data suggest that, in those lineages in which the gene copy was successfully recruited as HSS, the gene duplication event was followed by phases of various selection pressures, including purifying selection, relaxed functional constraints, and possibly positive Darwinian selection. Site-specific mutagenesis experiments have confirmed that the substitution of sites predicted to be under positive Darwinian selection is sufficient to convert a deoxyhypusine synthase into a HSS. In addition, analyses of transcript levels have shown that HSS and deoxyhypusine synthase have also diverged with respect to their regulation. The impact of protein–protein interaction on the evolution of HSS is discussed with respect to current models of enzyme evolution.

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“…This reaction is a well-known detoxification mechanism that has been demonstrated for several specialized insects that sequester PAs from their food plants and utilize them for their own benefit (Hartmann and Ober 2008). We never detected any significant N-oxidation of tertiary PAs in bees (data not shown).…”

Section: Discussionmentioning

confidence: 56%

“…The structural prerequisite here is the concurrent presence of the 1,2-double bond and an allylic ester functionality. Similar mechanisms can be assumed for mutagenic and toxic effects observed in insects (Frei et al 1992;Narberhaus et al 2005;Hartmann and Ober 2008).…”

Section: Introductionmentioning

confidence: 85%

“…These adaptations range from tolerance mediated by fast excretion rates (Lindigkeit et al 1997;Sadasivam and Thayumanavan 2003), to sequestration, safe storage, and integration into the insect-specific defense. The latter often includes sophisticated biochemical and behavioral adaptations that in leptidopterans guarantee optimal protection of the eggs, the most vulnerable stage in insect metamorphosis, from predators and parasitoids (for review see Eisner et al 2002;Hartmann and Ober 2008).…”

Section: Introductionmentioning

confidence: 99%

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Feeding Deterrence and Detrimental Effects of Pyrrolizidine Alkaloids Fed to Honey Bees (Apis mellifera)

et al. 2009

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Recent studies have shown the occurrence of plant derived pyrrolizidine alkaloids (PAs) in retail honeys and pollen loads, but little is known about how these compounds influence the fitness of foraging honey bees. In feeding experiments, we tested a mix of tertiary PAs and the corresponding N-oxides from Senecio vernalis, pure monocrotaline, and 1,2-dihydromonocrotaline in 50% (w/w) sucrose solutions. The bees were analyzed chemically to correlate the observed effects to the ingested amount of PAs. PA-N-oxides were deterrent at concentrations >0.2%. 1,2-Unsaturated tertiary PAs were toxic at high concentrations. The observed PAs mortality could be linked directly to the presence of the 1,2-double bond, a well established essential feature of PA cytotoxicity. In contrast, feeding experiments with 1,2-dihydromonocrotaline revealed no toxic effects. Levels of less than 50 microg 1,2-unsaturated tertiary PAs per individual adult bee were tolerated without negative effects. PA-N-oxides fed to bees were reduced partially to the corresponding tertiary PAs. Unlike some specialized insects, bees are not able to actively detoxify PAs through N-oxidation. To gain insight into how PAs are transmitted among bees, we tested for horizontal PA transfer (trophallaxis). Under laboratory conditions, up to 15% of an ingested PA diet was exchanged from bee to bee, disclosing a possible route for incorporation into the honey comb. In the absence of alternative nectar and pollen sources, PA-containing plants might exhibit a threat to vulnerable bee larvae, and this might affect the overall colony fitness.

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Defense by Pyrrolizidine Alkaloids: Developed by Plants and Recruited by Insects

Cited by 30 publications

References 89 publications

Homospermidine in transgenic tobacco results in considerably reduced spermidine levels but is not converted to pyrrolizidine alkaloid precursors

Homospermidine in transgenic tobacco results in considerably reduced spermidine levels but is not converted to pyrrolizidine alkaloid precursors

Evolution of Homospermidine Synthase in the Convolvulaceae: A Story of Gene Duplication, Gene Loss, and Periods of Various Selection Pressures

Feeding Deterrence and Detrimental Effects of Pyrrolizidine Alkaloids Fed to Honey Bees (Apis mellifera)

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