This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: Se volatilization II, Se-compound volatilization II, selenium compound volatilization II, Se-amino acid detoxification and volatilization II, dimethyl selenide biosynthesis II, seleno-amino acid detoxification and volatilization via DMSeP
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Selenium Metabolism → Seleno-Amino Acid Detoxification|
|Detoxification → Seleno-Amino Acid Detoxification|
Expected Taxonomic Range: Viridiplantae
Selenium is an essential micronutrient for animals and humans but has not yet been proven to be an essential micronutrient for land plants [Brown01a, Sors05]. There is evidence, however, of Chlamydomonas proteins that contains a L-selenocysteine residue suggesting that algal species might also require Se0 [Kim06b, Novoselov02]. The health requirement of Se0 for humans and animals can be met by crops and forage plants that contain selenocompounds. Helianthus annuus among the oilseed crops was shown to be a good source for this micronutrient [Terry00]. In addition, there is evidence that certain seleno-compounds, including seleno-L-methionine, have anti-carcinogenic properties [Whanger04].
Despite its importance as a micronutrient, higher concentrations of Se0 are toxic to humans, other animals, and plants largely because transporters and enzymes involved in sulfur and sulfo-compound metabolism can often erroneously substitute Se0 for sulfur and can misincorporate seleno-amino acids into proteins [Zwolak11, Ellis03, Brown81a].
In general, plants take up both selenate and selenite from soil. A series of reduction steps converts selenate to selenide / hydrogen selenide and this is assimilated into the seleno-amino acids L-selenocysteine and seleno-L-methionine [Sors09].
In Se accumulator plants, these seleno-amino acids may be modified to create organic seleno-compounds for storage. Seasonal weeds like Silene gallica and Avena sterilis ludoviciana along with perennial weeds like Cirsium arvense employ this strategy and accumulate high amounts of Se0 [Dhillon09]. Se accumulation can help to protect plants against attacks by prairie dogs, insects, and fungi (see refs in [Freeman09]).
Other plants, like Arabidopsis thaliana col generate seleno-compounds as well, but rather than storing them, they transform them into less toxic volatile compounds such as dimethyl selenide (DMSe) that can then be released from the plants [deSouza00]. This process is also called phytovolatilization [Zhou09].
While these strategies directly benefit the plants that employ them, they can also be put to use for the phytoremediation of seleniferous soils that contain dangerously high amounts of Se0. Numerous insights into endogenous seleno-compound metabolism in plants have been gained through efforts to engineer plants that show improved selenium phytoremediation abilities [Ellis04, Dhillon09, Zhou10a, Banuelos07, deSouza00].
About This Pathway
To reduce the risk of misincorporating seleno-L-methionine into proteins, this compound can be methylated to form the non-coding seleno-amino acid Se-methyl-Se-L-methionine. Some Se hyperaccumulating plants may sequester this compound.
Both Se-non-accumulators and accumulators may also further metabolize Se-methyl-Se-L-methionine to produce the volatile dimethyl selenide. This could occur in at least two manners. Many plants, such as Arabidopsis, may simply break down Se-methyl-Se-L-methionine in a one-step process that could be based on chemical decomposition or enzyme catalysis [Tagmount02].
However, as depicted in this pathway, halophytic species likely produce dimethyl selenide through a four-step process that mimics their dimethylsulfoniopropionate (DMSP) biosynthesis pathway. In Brassica juncea the intermediate compound dimethylselenoniopropanoate serves as an excellent precursor for dimethyl selenide production [deSouza00]. Moreover, there is evidence that Sporobolus alterniflorus produces dimethylselenoniopropanoate when grown in the presence of elevated levels of selenate, providing further support for this biosynthetic route in planta [Ansede99]. The Spartina enzymes shown to function in DMSP biosynthesis [Kocsis00] may perform analogous functions in DMSeP production.
Superpathways: superpathway of seleno-compound metabolism
Unification Links: PlantCyc:PWY-6935
Ansede99: Ansede, J.H., Pellechia, P.J., Yoch, D.C. (1999). "Selenium Biotransformation by the Salt Marsh Cordgrass Spartina alterniflora: Evidence for DimethylselenoniopropionateFormation." Environmental Science and Techonology. 33: 2064-2069.
Banuelos07: Banuelos GS, Lin ZQ (2007). "Acceleration of selenium volatilization in seleniferous agricultural drainage sediments amended with methionine and casein." Environ Pollut 150(3);306-12. PMID: 17445958
deSouza00: de Souza MP, Lytle CM, Mulholland MM, Otte ML, Terry N (2000). "Selenium assimilation and volatilization from dimethylselenoniopropionate by Indian mustard." Plant Physiol 122(4);1281-8. PMID: 10759525
Dhillon09: Dhillon KS, Dhillon SK (2009). "Selenium concentrations of common weeds and agricultural crops grown in the seleniferous soils of northwestern India." Sci Total Environ 407(24);6150-6. PMID: 19800657
Ellis04: Ellis DR, Sors TG, Brunk DG, Albrecht C, Orser C, Lahner B, Wood KV, Harris HH, Pickering IJ, Salt DE (2004). "Production of Se-methylselenocysteine in transgenic plants expressing selenocysteine methyltransferase." BMC Plant Biol 4;1. PMID: 15005814
Freeman09: Freeman JL, Quinn CF, Lindblom SD, Klamper EM, Pilon-Smits EA (2009). "Selenium protects the hyperaccumulator Stanleya pinnata against black-tailed prairie dog herbivory in native seleniferous habitats." Am J Bot 96(6);1075-85. PMID: 21628258
Kocsis00: Kocsis MG, Hanson AD (2000). "Biochemical evidence for two novel enzymes in the biosynthesis of 3-dimethylsulfoniopropionate in Spartina alterniflora." Plant Physiol 123(3);1153-61. PMID: 10889264
Novoselov02: Novoselov SV, Rao M, Onoshko NV, Zhi H, Kryukov GV, Xiang Y, Weeks DP, Hatfield DL, Gladyshev VN (2002). "Selenoproteins and selenocysteine insertion system in the model plant cell system, Chlamydomonas reinhardtii." EMBO J 21(14);3681-93. PMID: 12110581
Sors09: Sors TG, Martin CP, Salt DE (2009). "Characterization of selenocysteine methyltransferases from Astragalus species with contrasting selenium accumulation capacity." Plant J 59(1);110-22. PMID: 19309459
Tagmount02: Tagmount A, Berken A, Terry N (2002). "An essential role of s-adenosyl-L-methionine:L-methionine s-methyltransferase in selenium volatilization by plants. Methylation of selenomethionine to selenium-methyl-L-selenium- methionine, the precursor of volatile selenium." Plant Physiol 130(2);847-56. PMID: 12376649
Zhou09: Zhou X, Yuan Y, Yang Y, Rutzke M, Thannhauser TW, Kochian LV, Li L (2009). "Involvement of a broccoli COQ5 methyltransferase in the production of volatile selenium compounds." Plant Physiol 151(2);528-40. PMID: 19656903
Ansede97: Ansede, J.H., Yoch, D.C. (1997). "Comparison of selenium and sulfur volatilization by dimethylsulfoniopropionate lyase (DMSP) in two marine bacteria and estuarine sedimentsAnsede, J.H.; Yoch, D.C.; . 23, 315-324 (1997)." FEMS Microbiology Ecology. 23(4): 315-324.
Lyi05: Lyi SM, Heller LI, Rutzke M, Welch RM, Kochian LV, Li L (2005). "Molecular and biochemical characterization of the selenocysteine Se-methyltransferase gene and Se-methylselenocysteine synthesis in broccoli." Plant Physiol 138(1);409-20. PMID: 15863700
©2016 SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025-3493