# Mangotoxin

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**Mangotoxin** is a [phytotoxin](/source/Phytotoxin) produced by the bacterium *[Pseudomonas](/source/Pseudomonas)* [*syringae*](/source/Pseudomonas_syringae) that causes apical necrosis in [mango](/source/Mango) plants and [chlorosis](/source/Chlorosis) in other plants. It disrupts plant [metabolism](/source/Metabolism) by inhibiting ornithine acetyltransferase, an enzyme involved in [ornithine](/source/Ornithine) and [arginine](/source/Arginine) [biosynthesis](/source/Biosynthesis).[1] In disease, it also acts as a [virulence factor](/source/Virulence_factor) by weakening plant defenses.[2]

## Mbo operon

The proteins required for mangotoxin biosynthesis are encoded by the genes in *mangotoxin biosynthetic [operon](/source/Operon)* (*mbo*), which were identified using random mini-Tn5 mutagenesis, and subsequent cloning, sequencing, and expression.[3] The *mbo* operon consist of six genes: *mboA, mboB, mboC, mboD, mboE*, and *mboF*. All of them are required for the synthesis, and if any of these genes were disrupted, it could result in mangotoxin production deficiency. Other genes involved in the regulation of mangotoxin biosynthesis are the GacS/GacA genes and the mangotoxin generating operon (*mgo*).[1] The MgoA protein increases expression of *mbo*, but lack of MgoA is not enough to silence the *mbo*.[4] The GacS/GacA genes is highly conserved in Gram-negative bacteria, and controls [pathogenicity](/source/Pathogenesis), [quorum sensing](/source/Quorum_sensing), [secondary metabolite](/source/Secondary_metabolite) production, and [biofilm formation](/source/Biofilm). In *[Pseudomonas](/source/Pseudomonas)* [*syringae*](/source/Pseudomonas_syringae), the GacS/GacA gene regulates the production of multiple phytotoxins like [syringomycin](/source/Syringomycin_E), syringopeptin, [tabtoxin](/source/Tabtoxin), and phaseolotoxin.[3]

## Mgo operon

The *mgo* operon consists of four genes: mgoB, mgoC, mgoA, and mgoD. Mutations in mgoC, mgoA, and mgoD have shown a lack of mangotoxin production, while a mutation in mgoB showed an alteration. These genes are predicted to encode for proteins for a [haem oxygenase](/source/Heme_oxygenase) (mgoB), a *p*-aminobenzoate *N*-oxygenase (MgoC), a [nonribosomal peptide synthetase](/source/Nonribosomal_peptide_synthetase) (NRPs) (mgoA), and a polyketide cyclase/dehydrase or lipid transporter (MgoD).[3] The *mgo* operon is a positive regulator of the *mbo* operon.

## Ornithine and arginine biosynthesis

In the biosynthesis of ornithine and arginine, mangotoxin specifically targets ornithine [N-acetyltransferase](/source/N-acetyltransferase) (OAT), which is a key enzyme in the synthesis of ornithine and arginine. OAT catalyzes the transfer of the acetyl group from N-acetylornithine (NAO) to [glutamate](/source/Glutamate), producing [N-acetylglutamate](/source/N-acetylglutamate) and ornithine. Mangotoxin acts as an [antimetabolite](/source/Antimetabolite) inhibitor of OAT, leading to an accumulation of NAO and [glutamate](/source/Glutamate_(neurotransmitter)), causing a depletion of intracellular ornithine and arginine. In some bacteria, such as *[Enterobacteriaceae](/source/Enterobacteriaceae),* NAO can be converted to orthithine by [acetylornithine deacetylase](/source/Acetylornithine_deacetylase) (AO), that may also be inhibited by mangotoxin. Similarly, such inhibition can also be seen in [*p*-chloromercuribenzoic acid](/source/4-Chloromercuribenzoic_acid) (PCMB), a chemical inhibitor of OAT and AO. From Arrebola et al.'s findings, it can demonstrate that mangotoxin disrupts a certain step of the arginine biosynthesis pathway, specifically the OAT enzyme. However, mangotoxin's metabolic step differs from other *[Pseudomonas](/source/Pseudomonas)* [*syringae*](/source/Pseudomonas_syringae) toxins, such as tabtoxins, which inhibits [glutamine synthetase](/source/Glutamine_synthetase) (GS), or phaseolotoxin, which inhibits [ornithine carbamoyltransferase](/source/Ornithine_transcarbamylase) (OCT).[citation needed]

The mangotoxin related genes and their homologues are common in *[Pseudomonas](/source/Pseudomonas)*, and they also appear also in other phyla, like *[Burkholderia](/source/Burkholderia)*. Their purpose is to produce toxin to kill other competing microbes, like [fungi](/source/Fungus) or [oomycetes](/source/Oomycete).[5]

## References

1. Carrión, Víctor J.; Arrebola, Eva; Cazorla, Francisco M.; Murillo, Jesús; de Vicente, Antonio (17 May 2012). "The mbo Operon Is Specific and Essential for Biosynthesis of Mangotoxin in Pseudomonas syringae". *PLOS ONE*. **7** (5). [Bibcode:2012PLoSO...736709C](https://ui.adsabs.harvard.edu/abs/2012PLoSO...736709C). [doi:10.1371/journal.pone.0036709](https://doi.org/10.1371/journal.pone.0036709). [PMC 3355146](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355146). [PMID 22615797](https://pubmed.ncbi.nlm.nih.gov/22615797)

1. Arrebola, Eva; Cazorla, Francisco M; Durán, Victoria E; Rivera, Eugenia; Olea, Francisco; Codina, Juan C; Pérez-Garcı́a, Alejandro; de Vicente, Antonio (September 2003). "Mangotoxin: a novel antimetabolite toxin produced by Pseudomonas syringae inhibiting ornithine/arginine biosynthesis". *Physiological and Molecular Plant Pathology*. **63** (3): 117–127. [Bibcode:2003PMPP...63..117A](https://ui.adsabs.harvard.edu/abs/2003PMPP...63..117A). [doi:10.1016/j.pmpp.2003.11.003](https://doi.org/10.1016/j.pmpp.2003.11.003)

1. Carrión, Víctor J; van der Voort, Menno; Arrebola, Eva; Gutiérrez-Barranquero, José A; de Vicente, Antonio; Raaijmakers, Jos M; Cazorla, Francisco M (December 2014). "Mangotoxin production of Pseudomonas syringae pv. syringae is regulated by MgoA". *BMC Microbiology*. **14** (1). [doi:10.1186/1471-2180-14-46](https://doi.org/10.1186/1471-2180-14-46). [PMC 3945005](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3945005). [PMID 24555804](https://pubmed.ncbi.nlm.nih.gov/24555804)

1. Guo, Qiang; Vitro, Caitlin N.; Crawford, Drake M.; Li, Bo (2024-08-15). "A diazeniumdiolate signal in Pseudomonas syringae upregulates virulence factors and promotes survival in plants". *Molecular Plant-Microbe Interactions*. **37** (11): 776–783. [Bibcode:2024MPMI...37..776G](https://ui.adsabs.harvard.edu/abs/2024MPMI...37..776G). [doi:10.1094/MPMI-06-24-0069-R](https://doi.org/10.1094/MPMI-06-24-0069-R). [PMID 39146356](https://pubmed.ncbi.nlm.nih.gov/39146356)

1. Kremmydas, Gerasimos F.; Tampakaki, Anastasia P.; Georgakopoulos, Dimitrios G. (15 April 2013). "Characterization of the Biocontrol Activity of Pseudomonas fluorescens Strain X Reveals Novel Genes Regulated by Glucose". *PLOS ONE*. **8** (4). [Bibcode:2013PLoSO...861808K](https://ui.adsabs.harvard.edu/abs/2013PLoSO...861808K). [doi:10.1371/journal.pone.0061808](https://doi.org/10.1371/journal.pone.0061808). [PMC 3626644](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3626644). [PMID 23596526](https://pubmed.ncbi.nlm.nih.gov/23596526)

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Adapted from the Wikipedia article [Mangotoxin](https://en.wikipedia.org/wiki/Mangotoxin) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mangotoxin?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.