If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: sporopollenin monomer biosynthesis
|Superclasses:||Biosynthesis → Cell Structures Biosynthesis → Plant Cell Structures|
Some taxa known to possess this pathway include : Arabidopsis thaliana col
Expected Taxonomic Range: Embryophyta
The pollen grain wall in most plant species has the same basic structure, although the size, shape and external morphology are species-specific. It consists of an outer and inner layer, called the exine and intine, respectively. The exine consists of an outer sculptured portion, the sexine, and a simpler inner layer, the nexine. The sculptured sexine is made up of radially directed rods, the bacula, which have enlarged heads that fuse to form a patterned wall, and the tectum, which is the outermost edge of the exine. The exine wall has important roles in protecting the pollen from various environmental stresses and bacterial attacks when it moves from the anther to the stigma, and in the species-specific adhesion of pollen grains to the female stigma cells [Ariizumi03].
The interstices of the exine are coated with a sticky hydrophobic lipidic and proteinaceous layer known as the tryphine or pollen coat. A mojor component of the tryphine is sporopollenin - a complex polymer that confers physical strength, chemical inertness and elasticity to the exine. The chemical composition of sporopollenin remains poorly characterized due to its extreme resistance to chemical and biological degradations. However limited data indicates the presence of aliphatic polyhydroxy compounds and phenolic hydroxyl groups [Ahlers03]. Several genes and their encoded enzymes involved in sporopollenin biosynthesis have been identified in the recent years [Grienenberger10, Dobritsa09, Kim10f, Morant07, deAzevedo09]. The genetic and biochemical data further suggest that sporopollenin components include hydroxylated fatty acids and their derived tetraketide α-pyrones. The sporopollenin components are presumably coupled with ester and ether linkages. Nonetheless, the exact chemical nature of the sporopollenin polymer and its components still remains to be elucidated. For example, although in vitro enzyme characterization supports the presence of tetraketide α-pyrones, their occurrence has not been reported in Arabidopsis.
About This Pathway
The pathway starts with fatty acids synrthesized in the plastid - laurate, palmitate, stearate and oleate. These fatty acids are exported from the plastid and imported into the endoplasmic reticulum (ER) in their CoA-activated forms. Once they enter the ER, they are believed to be hydrolyzed to free fatty acids that are hydroxylated by P450 fatty acid monooxygenases. Two routes have been described. Laurate (C12:0) is hydroxylated at position 7 by a dedicated monooxygenase, encoded by the CYP703A2 gene [Morant07]. The other three fatty acids are hydroxylated at the ω position by long-chain fatty acid ω-hydroxylase, encoded by CYP704B1 [Dobritsa09]. Once hydroxylated, the fatty acids are again esterified to coenzyme A in a reaction catalyzed by the fatty acyl-CoA synthetase encoded by ACOS5 [deAzevedo09] and exported from the ER to the cytosol. .
The processes in the cytosol are not well understood, but a few enzymes are known to be involved. The alcohol-forming fatty acyl-CoA reductase encoded by the FAR2 gene is absoltely required, and is assumed to convert the hydroxylated fatty acyl-CoAs to fatty alcohols [Aarts97]. 7-hydroxylauroyl-CoA is also the substrate for the tetraketide α-pyrone synthases encoded by PKSA and PKSB, which convert it to the tetraketide α-pyrone 2-(8-hydroxy-2-oxotridecyl)-6-oxopyran-4-olate [Kim10f].
The genes involved in this pathway, CYP704B1, CYP703A2, ACOS5, PKSA, PKSB, TKPR1 and TKPR2, are tightly co-expressed.
Aarts97: Aarts MG, Hodge R, Kalantidis K, Florack D, Wilson ZA, Mulligan BJ, Stiekema WJ, Scott R, Pereira A (1997). "The Arabidopsis MALE STERILITY 2 protein shares similarity with reductases in elongation/condensation complexes." Plant J 12(3);615-23. PMID: 9351246
Ahlers03: Ahlers F, Lambert J, Wiermann R (2003). "Acetylation and silylation of piperidine solubilized sporopollenin from pollen of Typha angustifolia L." Z Naturforsch C 58(11-12);807-11. PMID: 14713155
Ariizumi03: Ariizumi T, Hatakeyama K, Hinata K, Sato S, Kato T, Tabata S, Toriyama K (2003). "A novel male-sterile mutant of Arabidopsis thaliana, faceless pollen-1, produces pollen with a smooth surface and an acetolysis-sensitive exine." Plant Mol Biol 53(1-2);107-16. PMID: 14756310
deAzevedo09: de Azevedo Souza C, Kim SS, Koch S, Kienow L, Schneider K, McKim SM, Haughn GW, Kombrink E, Douglas CJ (2009). "A novel fatty Acyl-CoA Synthetase is required for pollen development and sporopollenin biosynthesis in Arabidopsis." Plant Cell 21(2);507-25. PMID: 19218397
Dobritsa09: Dobritsa AA, Shrestha J, Morant M, Pinot F, Matsuno M, Swanson R, Moller BL, Preuss D (2009). "CYP704B1 is a long-chain fatty acid omega-hydroxylase essential for sporopollenin synthesis in pollen of Arabidopsis." Plant Physiol 151(2);574-89. PMID: 19700560
Grienenberger10: Grienenberger E, Kim SS, Lallemand B, Geoffroy P, Heintz D, Souza Cde A, Heitz T, Douglas CJ, Legrand M (2010). "Analysis of TETRAKETIDE α-PYRONE REDUCTASE function in Arabidopsis thaliana reveals a previously unknown, but conserved, biochemical pathway in sporopollenin monomer biosynthesis." Plant Cell 22(12);4067-83. PMID: 21193572
Kim10f: Kim SS, Grienenberger E, Lallemand B, Colpitts CC, Kim SY, Souza Cde A, Geoffroy P, Heintz D, Krahn D, Kaiser M, Kombrink E, Heitz T, Suh DY, Legrand M, Douglas CJ (2010). "LAP6/POLYKETIDE SYNTHASE A and LAP5/POLYKETIDE SYNTHASE B encode hydroxyalkyl α-pyrone synthases required for pollen development and sporopollenin biosynthesis in Arabidopsis thaliana." Plant Cell 22(12);4045-66. PMID: 21193570
Morant07: Morant M, Jorgensen K, Schaller H, Pinot F, Moller BL, Werck-Reichhart D, Bak S (2007). "CYP703 is an ancient cytochrome P450 in land plants catalyzing in-chain hydroxylation of lauric acid to provide building blocks for sporopollenin synthesis in pollen." Plant Cell 19(5);1473-87. PMID: 17496121
Bais10: Bais P, Moon SM, He K, Leitao R, Dreher K, Walk T, Sucaet Y, Barkan L, Wohlgemuth G, Roth MR, Wurtele ES, Dixon P, Fiehn O, Lange BM, Shulaev V, Sumner LW, Welti R, Nikolau BJ, Rhee SY, Dickerson JA (2010). "PlantMetabolomics.org: a web portal for plant metabolomics experiments." Plant Physiol 152(4);1807-16. PMID: 20147492
Benveniste98: Benveniste I, Tijet N, Adas F, Philipps G, Salaun JP, Durst F (1998). "CYP86A1 from Arabidopsis thaliana encodes a cytochrome P450-dependent fatty acid omega-hydroxylase." Biochem Biophys Res Commun 243(3);688-93. PMID: 9500987
Chi09: Chi A, Rhee S (2009). "The functional annotation of Arabidopsis protein sequences was performed by BLAST queries against a reference set of experimentally verified enzymes. For each Arabidopsis sequence, the enzymatic activity of the top BLAST hit (or hits if they had equivalent E-values) was assigned to the protein if its E-value fell below a specific E-value threshold established for the corresponding enzymatic activity. Note: The annotation thresholds were established by doing a self BLAST of the reference enzyme dataset. For each enzymatic activity represented by multiple proteins, the mean E-value of all the correct hits generated by the self BLAST was selected as the cut-off. All of these means were averaged and used as the cut-off for assigning annotations for any enzymatic activities that were represented by a single protein in the reference dataset."
Doan09: Doan TT, Carlsson AS, Hamberg M, Bulow L, Stymne S, Olsson P (2009). "Functional expression of five Arabidopsis fatty acyl-CoA reductase genes in Escherichia coli." J Plant Physiol 166(8);787-96. PMID: 19062129
Goldfine71: Goldfine H, Panos C (1971). "Phospholipids of Clostridium butyricum. IV. Analysis of the positional isomers of monounsaturated and cyclopropane fatty acids and alk-1'-enyl ethers by capillary column chromatography." J Lipid Res 12(2);214-20. PMID: 5554109
Gross06: Gross J, Cho WK, Lezhneva L, Falk J, Krupinska K, Shinozaki K, Seki M, Herrmann RG, Meurer J (2006). "A plant locus essential for phylloquinone (vitamin K1) biosynthesis originated from a fusion of four eubacterial genes." J Biol Chem 281(25);17189-96. PMID: 16617180
Hofer08: Hofer R, Briesen I, Beck M, Pinot F, Schreiber L, Franke R (2008). "The Arabidopsis cytochrome P450 CYP86A1 encodes a fatty acid omega-hydroxylase involved in suberin monomer biosynthesis." J Exp Bot 59(9);2347-60. PMID: 18544608
Hunt06: Hunt MC, Rautanen A, Westin MA, Svensson LT, Alexson SE (2006). "Analysis of the mouse and human acyl-CoA thioesterase (ACOT) gene clusters shows that convergent, functional evolution results in a reduced number of human peroxisomal ACOTs." FASEB J 20(11);1855-64. PMID: 16940157
Imaishi07: Imaishi H, Petkova-Andonova M (2007). "Molecular cloning of CYP76B9, a cytochrome P450 from Petunia hybrida, catalyzing the omega-hydroxylation of capric acid and lauric acid." Biosci Biotechnol Biochem 71(1);104-13. PMID: 17213671
Isbell06: Isbell, T.A, Lowery, B.A, DeKeyser, S.S, Winchell, A.L, Cermak, S.C (2006). "Physical properties of triglyceride estolides from lesquerella and castor oils." Industrial Crops and Products, 23, 256-263.
Jaworski74: Jaworski JG, Stumpf PK (1974). "Fat metabolism in higher plants. Properties of a soluble stearyl-acyl carrier protein desaturase from maturing Carthamus tinctorius." Arch Biochem Biophys 162(1);158-65. PMID: 4831331
Jiang08: Jiang M, Chen X, Guo ZF, Cao Y, Chen M, Guo Z (2008). "Identification and Characterization of (1R,6R)-2-Succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate Synthase in the Menaquinone Biosynthesis of Escherichia coli." Biochemistry 47(11);3426-34. PMID: 18284213
Jiang09: Jiang M, Chen X, Wu XH, Chen M, Wu YD, Guo Z (2009). "Catalytic mechanism of SHCHC synthase in the menaquinone biosynthesis of Escherichia coli: identification and mutational analysis of the active site residues." Biochemistry 48(29);6921-31. PMID: 19545176
Kandel07: Kandel S, Sauveplane V, Compagnon V, Franke R, Millet Y, Schreiber L, Werck-Reichhart D, Pinot F (2007). "Characterization of a methyl jasmonate and wounding-responsive cytochrome P450 of Arabidopsis thaliana catalyzing dicarboxylic fatty acid formation in vitro." FEBS J 274(19);5116-27. PMID: 17868380
Kuznetsova05: Kuznetsova E, Proudfoot M, Sanders SA, Reinking J, Savchenko A, Arrowsmith CH, Edwards AM, Yakunin AF (2005). "Enzyme genomics: Application of general enzymatic screens to discover new enzymes." FEMS Microbiol Rev 29(2);263-79. PMID: 15808744
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