Directed Biosynthesis of Phytotoxic Alkaloids in the Cyanobacterium Nostoc 78-12A

Nostocarboline, a chlorinated and N-methylated carbolinium alkaloid, displays potent and selective inhibition of photoautotrophic organisms as well as the malaria parasite Plasmodium falciparum, while showing very low toxicity to bacterial and fungal pathogens, rat myoblasts and crustaceans. New derivatives of nostocarboline incorporating Br, F or methyl substituents have been obtained through precursor-directed biosynthesis in Nostoc 78-12A (identical to Nostoc sp. ATCC 43238) by feeding this cyanobacterium with differently substituted tryptophan derivatives or 6-Br-norharmane (eudistomin N). These experiments substantiate the biosynthetic hypothesis and validate the inherent flexibility of the corresponding enzymes for metabolic engineering. The new derivatives inhibit the growth of the toxic-bloom-forming cyanobacterium Microcystis aeruginosa PCC 7806 above 1 μM. The mode of action of nostocarboline was investigated by using chlorophyll-a fluorescence imaging, and it was demonstrated that a decrease in photosynthesis precedes cell death, thus establishing the phytotoxic properties of this alkaloid

Rapid metabolic profiling of Nicotiana tabacum defence responses against Phytophthora nicotianae using direct infrared laser desorption ionization mass spectrometry and principal component analysis

<p>Abstract</p> <p>Background</p> <p>Successful defence of tobacco plants against attack from the oomycete <it>Phytophthora nicotianae </it>includes a type of local programmed cell death called the hypersensitive response. Complex and not completely understood signaling processes are required to mediate the development of this defence in the infected tissue. Here, we demonstrate that different families of metabolites can be monitored in small pieces of infected, mechanically-stressed, and healthy tobacco leaves using direct infrared laser desorption ionization orthogonal time-of-flight mass spectrometry. The defence response was monitored for 1 - 9 hours post infection.</p> <p>Results</p> <p>Infrared laser desorption ionization orthogonal time-of-flight mass spectrometry allows rapid and simultaneous detection in both negative and positive ion mode of a wide range of naturally occurring primary and secondary metabolites. An unsupervised principal component analysis was employed to identify correlations between changes in metabolite expression (obtained at different times and sample treatment conditions) and the overall defence response.</p> <p>A one-dimensional projection of the principal components 1 and 2 obtained from positive ion mode spectra was used to generate a Biological Response Index (BRI). The BRI obtained for each sample treatment was compared with the number of dead cells found in the respective tissue. The high correlation between these two values suggested that the BRI provides a rapid assessment of the plant response against the pathogen infection. Evaluation of the loading plots of the principal components (1 and 2) reveals a correlation among three metabolic cascades and the defence response generated in infected leaves. Analysis of selected phytohormones by liquid chromatography electrospray ionization mass spectrometry verified our findings.</p> <p>Conclusion</p> <p>The described methodology allows for rapid assessment of infection-specific changes in the plant metabolism, in particular of phenolics, alkaloids, oxylipins, and carbohydrates. Moreover, potential novel biomarkers can be detected and used to predict the quality of plant infections.</p

Regulatory subunit B'gamma of protein phosphatase 2A prevents unnecessary defense reactions under low light in Arabidopsis

Peer reviewe

Charakterisierung von zwei Stress-induzierbaren Serin/Threonin-Proteinkinasen und eines Transkriptionsfaktors der AP2/EREBP-Familie bei Mesembryanthemum crystallinum L.

Zwei Stress-induzierbare Ser-/Thr-Proteinkinasen (MK5,MK6) wurden aus der fakultativen CAM-Pflanze M. crystallinum L., einer Modellpflanze für Untersuchungen des Crassulaceen-Säurestoffwechsels (CAM), kloniert und charakterisiert. Mittels Hefe-Dihybrid-System wurde zudem ein Transkriptionsfaktor (CDBP) der AP2/EREBP-Familie als möglicher Interaktionspartner von MK5 identifiziert. Mit MK6 wurde ein ABA-sensitiver, mit MK5 und CDBP ein ABA-insensitiver Teil der Signaltransduktion zur Stress-Adaptation charakterisiert. "Cross talks" zwischen diesen Signalwegen könnten M. crystallinum L. zu der hochkomplexen Salzstressanpassung befähigen, die neben physiologischen Reaktionen (z.B. CAM) eine Vielzahl morphologischer Veränderungen (z.B. Blasenzellen, Sekundärblätter) und schließlich auch die Induktion von Entwicklungsprozessen (z.B. Blühinduktion, Seneszenz) einschließen. Dazu ist ein differentes Netzwerk von Signalwegen erforderlich, wobei mit den hier charakterisierten stress-induzierbaren Proteinen möglicherweise neue Ansatzpunkte für tiefergehende Studien dieses Netzwerkes gefunden wurden