CAZypedia needs your help!
We have many unassigned pages in need of Authors and Responsible Curators. See a page that's out-of-date and just needs a touch-up? - You are also welcome to become a CAZypedian. Here's how.
Scientists at all career stages, including students, are welcome to contribute.
Learn more about CAZypedia's misson here and in this article.
Totally new to the CAZy classification? Read this first.

Glycoside Hydrolase Family 9/Plant endoglucanases

From CAZypedia
Jump to navigation Jump to search
Approve icon-50px.png

This page has been approved by the Responsible Curator as essentially complete. CAZypedia is a living document, so further improvement of this page is still possible. If you would like to suggest an addition or correction, please contact the page's Responsible Curator directly by e-mail.

Note: This page is an extension of the Glycoside Hydrolase Family 9 page, which is focussed on a key subgroup enzymes from plants. Please see the main GH9 page for full information on the functional and structural properties of these enzymes.


Early reports described the existence of plant "cellulases" or EGases [1]. Subsequently, cellulases have been shown to be associated with plant cell wall restructuring during cell expansion, the wall disassembly that accompanies processes such as fruit ripening and abscission (reviewed in [2, 3, 4]) and cellulose biosynthesis [5, 6, 7]. The amino acid sequences of the first plant "cellulases"/endo-ß-1,4-glucanases revealed that these enzymes belong to the CAZy family GH9 glycoside hydrolases [8].

Most plant GH9 glycoside hydrolases are endoglucanases ("cellulases", EC with low or no activity on crystalline cellulose, but with discernible activity on soluble cellulose derivatives, including carboxymethyl cellulose (CMC), phosphoric acid swollen non-crystalline cellulose, and numerous plant polysaccharides including xylan, 1,3-1,4-ß-glucan, xyloglucan, and glucomannan [9, 10, 11, 12, 13]. The inability of plant “cellulases” to hydrolyze crystaline cellulose is distinct from microbial cellulases, whose modular structure and synergistic action with other enzymes facilitates effective degradation of crystalline cellulose. In muro, the substrates of plant cellulases may include xyloglucan, xylans, and non-crystalline cellulose, especially amorphous regions of cellulose where the microfibrils may be interwoven with xyloglucan.

Plant GH9 subfamilies

In the model plant Arabidopsis thaliana, 25 different GH9 coding regions have been identified. Phylogenic analysis of the deduced amino acid sequences group the proteins into nine classes or three subfamilies [4, 13, 14, 15]. Three distinct types of GH9 proteins are present in plants. Class A proteins are membrane-anchored, Class B proteins are secreted, and Class C proteins are also secreted but contain a family 49 carbohydrate binding module (CBM49) [13]. Recent bioinformatic studies suggest that the first gene duplication event that gave rise to the three plant GH9 sub-families took place prior to the divergence of angiosperms and gymnosperms about 300 million years ago, and most secondary duplication events occurred before the monocot/dicot divergence about 200 million years ago [16]. Class A plant EGases have been reported to lack tryptophans corresponding to substrate binding at subsites -4, -3, and -2 in T. fusca Cel9A [9]. Class C EGases are the only plant EGases to date that contain a tryptophan residue corresponding to the one in subsite -2 in TfCel9A [9, 13]. This tryptophan has been shown to be important for hydrolysis in TfCel9A, and the enzyme retains less than 10% of its normal activity on polymeric cellulose substrates, and less than 1% of wild type activity on cellohexaose when the Trp is replaced by another amino acid [9, 17].

Class A

The Class A EGases are integral type II membrane proteins with a GH9 catalytic core that lack a canonical secretion signal sequence. These enzymes are predicted to have a high degree of N-glycosylation and a long amino-terminal extension with a membrane-spanning domain that anchors the protein to the plasma membrane and/or to intracellular organelles [4, 18]. Membrane anchored EGases were first described in studies of the KORRIGAN (KOR) genes in Arabidopsis thaliana, which showed that they encode EGases that are required for normal cellulose synthesis or assembly. Plants with mutant alleles of the KOR1 gene are dwarfed, with decreased cellulose content and crystallinity [4, 19, 20]. The role of the Class A EGases in plants is not known. However, the KOR proteins have been proposed to cleave sitosterol-b-glucoside primers from the growing cellulose polymer, or may have a role in editing incorrectly formed growing microfibrils [21]. The catalytic domain of PttCel9A, a Class A GH9 enzyme that is upregulated during secondary cell wall synthesis in Populus tremula x tremuloides, has been biochemically characterized and shown to hydrolyse a narrow range of substrates in vitro including CMC, phosphoric acid swollen cellulose and cellulose oligosaccharides (DP≥5) [9, 22].

Previously, it was shown that during cell expansion, KOR1 is cycled from the plasma membrane through intracellular compartments, comprising both the Golgi apparatus and early endosomes; however the role of KOR1 in cellulose biosynthesis was unclear [23]. Recently, membrane-based split-ubiquitin assays and bimolecular fluorescence complementation have demonstrated a direct interaction between GH9A1/KOR1 and cellulose synthase isoforms (CESA1, CESA3 and CESA6) that comprise the primary cellulose synthase complex in Arabidopsis [24]. GH9A1/KOR1 has also been shown to co-localize with the cellulose synthase complex at the plant plasma membrane [25]. Two different mutations in KOR1 (kor1-1 and jiaoyao1 ) cause reduced motility of the cellulose synthase complex in the plasma membrane, suggesting a role for GH9A1/KOR1 in cellulose synthesis and intracellular trafficking of the complexes [24, 25]. Interestingly, the jiaoyao1 mutation is caused by a point mutation (C to T), which results in an amino acid substitution (A577V) within the second GH9 active site signature motif, eliminating the endoglucanase activity of the enzyme. This new data strongly suggests that the endoglucanase activity of GH9A1 is very important, but not essential, for proper cellulose biosynthesis in plants [25].

Class B

Class B proteins are the most common form of plant EGases and are associated with virtually all stages of plant growth and development. These enzymes have a GH9 catalytic domain and a signal sequence for ER targeting and secretion. Different isoforms are expressed during fruit ripening, in abscission zones, in reproductive organ development, and in expanding cells [26, 27, 28, 29]. Numerous studies, especially in tomato, have also shown that many class B EGases are under hormonal control [30, 31, 32].

Class C

Plant Class C GH9 enzymes are the least studied. These proteins are predicted to have a signal sequence followed by a GH9 catalytic domain and a long carboxyl-terminal extension, which contains a CBM49 that has been shown to bind to crystalline cellulose in vitro [13, 15]. CBMs are necessary for activity on crystalline substrates and may promote hydrolysis by increasing the local enzyme concentration at the substrate surface as well as modifying cellulose microfibril structure (for review see [33]). The catalytic domain (CD) SlGH9C1 from tomato is promiscuous and can effectively hydrolyze artificial cellulosic polymers, cellulose oligosaccharides, and several plant cell wall polysaccharides [13]. Nevertheless, the activity of the full length, modular enzyme has still not been characterized. A Class C EGase from rice, OsCel9A, has been shown to be post-translationaly modified at the linker region to yield a 51 kDa GH9 CD and a CBM49, and it was suggested that the cleavage is necessary for function [34]. The OsCel9A CD also displays a broad substrate range and was able to hydrolyze CMC, phosphoric acid-swollen cellulose, mixed linkage 1,3-1,4-ß-glucan, xylan, glucomannan, cellooligosaccharides (DP≥4) and 1,4-ß-xylohexaose [10]. For Information regarding nomenclature of plant GH9 enzymes please see Urbanowicz et al 2007 [15].


  1. HALL CB (1963). CELLULASE IN TOMATO FRUITS. Nature. 1963;200:1010-1. DOI:10.1038/2001010b0 | PubMed ID:14097721 [Hall1963]
  2. del Campillo E (1999). Multiple endo-1,4-beta-D-glucanase (cellulase) genes in Arabidopsis. Curr Top Dev Biol. 1999;46:39-61. DOI:10.1016/s0070-2153(08)60325-7 | PubMed ID:10417876 [Campillo1999]
  3. Rose JK and Bennett AB. (1999). Cooperative disassembly of the cellulose-xyloglucan network of plant cell walls: parallels between cell expansion and fruit ripening. Trends Plant Sci. 1999;4(5):176-183. DOI:10.1016/s1360-1385(99)01405-3 | PubMed ID:10322557 [Rose1999]
  4. Mølhøj M, Pagant S, and Höfte H. (2002). Towards understanding the role of membrane-bound endo-beta-1,4-glucanases in cellulose biosynthesis. Plant Cell Physiol. 2002;43(12):1399-406. DOI:10.1093/pcp/pcf163 | PubMed ID:12514237 [Molhoj2002]
  5. Nicol F, His I, Jauneau A, Vernhettes S, Canut H, and Höfte H. (1998). A plasma membrane-bound putative endo-1,4-beta-D-glucanase is required for normal wall assembly and cell elongation in Arabidopsis. EMBO J. 1998;17(19):5563-76. DOI:10.1093/emboj/17.19.5563 | PubMed ID:9755157 [Nicol1998]
  6. Lane DR, Wiedemeier A, Peng L, Höfte H, Vernhettes S, Desprez T, Hocart CH, Birch RJ, Baskin TI, Burn JE, Arioli T, Betzner AS, and Williamson RE. (2001). Temperature-sensitive alleles of RSW2 link the KORRIGAN endo-1,4-beta-glucanase to cellulose synthesis and cytokinesis in Arabidopsis. Plant Physiol. 2001;126(1):278-88. DOI:10.1104/pp.126.1.278 | PubMed ID:11351091 [Lane2001]
  7. Sato S, Kato T, Kakegawa K, Ishii T, Liu YG, Awano T, Takabe K, Nishiyama Y, Kuga S, Sato S, Nakamura Y, Tabata S, and Shibata D. (2001). Role of the putative membrane-bound endo-1,4-beta-glucanase KORRIGAN in cell elongation and cellulose synthesis in Arabidopsis thaliana. Plant Cell Physiol. 2001;42(3):251-63. DOI:10.1093/pcp/pce045 | PubMed ID:11266576 [Sato2001]
  8. Henrissat B (1991). A classification of glycosyl hydrolases based on amino acid sequence similarities. Biochem J. 1991;280 ( Pt 2)(Pt 2):309-16. DOI:10.1042/bj2800309 | PubMed ID:1747104 [Henrissat1991]
  9. Master ER, Rudsander UJ, Zhou W, Henriksson H, Divne C, Denman S, Wilson DB, and Teeri TT. (2004). Recombinant expression and enzymatic characterization of PttCel9A, a KOR homologue from Populus tremula x tremuloides. Biochemistry. 2004;43(31):10080-9. DOI:10.1021/bi049453x | PubMed ID:15287736 [Master2004]
  10. Yoshida K and Komae K. (2006). A rice family 9 glycoside hydrolase isozyme with broad substrate specificity for hemicelluloses in type II cell walls. Plant Cell Physiol. 2006;47(11):1541-54. DOI:10.1093/pcp/pcl020 | PubMed ID:17056618 [YoshidaKomae2006]
  11. Ohmiya Y, Samejima M, Shiroishi M, Amano Y, Kanda T, Sakai F, and Hayashi T. (2000). Evidence that endo-1,4-beta-glucanases act on cellulose in suspension-cultured poplar cells. Plant J. 2000;24(2):147-58. DOI:10.1046/j.1365-313x.2000.00860.x | PubMed ID:11069690 [Ohmiya2000]
  12. Woolley LC, James DJ, and Manning K. (2001). Purification and properties of an endo-beta-1,4-glucanase from strawberry and down-regulation of the corresponding gene, cel1. Planta. 2001;214(1):11-21. DOI:10.1007/s004250100577 | PubMed ID:11762160 [Woolley2001]
  13. Urbanowicz BR, Catalá C, Irwin D, Wilson DB, Ripoll DR, and Rose JK. (2007). A tomato endo-beta-1,4-glucanase, SlCel9C1, represents a distinct subclass with a new family of carbohydrate binding modules (CBM49). J Biol Chem. 2007;282(16):12066-74. DOI:10.1074/jbc.M607925200 | PubMed ID:17322304 [Urbanowicz2007]
  14. Libertini E, Li Y, and McQueen-Mason SJ. (2004). Phylogenetic analysis of the plant endo-beta-1,4-glucanase gene family. J Mol Evol. 2004;58(5):506-15. DOI:10.1007/s00239-003-2571-x | PubMed ID:15170254 [Libertini2004]
  15. Urbanowicz BR, Bennett AB, Del Campillo E, Catalá C, Hayashi T, Henrissat B, Höfte H, McQueen-Mason SJ, Patterson SE, Shoseyov O, Teeri TT, and Rose JK. (2007). Structural organization and a standardized nomenclature for plant endo-1,4-beta-glucanases (cellulases) of glycosyl hydrolase family 9. Plant Physiol. 2007;144(4):1693-6. DOI:10.1104/pp.107.102574 | PubMed ID:17687051 [UrbanowiczBennett2007]
  16. Du Q, Wang L, Yang X, Gong C, and Zhang D. (2015). Populus endo-β-1,4-glucanases gene family: genomic organization, phylogenetic analysis, expression profiles and association mapping. Planta. 2015;241(6):1417-34. DOI:10.1007/s00425-015-2271-y | PubMed ID:25716095 [Du2015]
  17. Li Y, Irwin DC, and Wilson DB. (2007). Processivity, substrate binding, and mechanism of cellulose hydrolysis by Thermobifida fusca Cel9A. Appl Environ Microbiol. 2007;73(10):3165-72. DOI:10.1128/AEM.02960-06 | PubMed ID:17369336 [Li2007]
  18. Brummell DA, Catala C, Lashbrook CC, and Bennett AB. (1997). A membrane-anchored E-type endo-1,4-beta-glucanase is localized on Golgi and plasma membranes of higher plants. Proc Natl Acad Sci U S A. 1997;94(9):4794-9. DOI:10.1073/pnas.94.9.4794 | PubMed ID:9114071 [Brummell1997a]
  19. Szyjanowicz PM, McKinnon I, Taylor NG, Gardiner J, Jarvis MC, and Turner SR. (2004). The irregular xylem 2 mutant is an allele of korrigan that affects the secondary cell wall of Arabidopsis thaliana. Plant J. 2004;37(5):730-40. DOI:10.1111/j.1365-313x.2003.02000.x | PubMed ID:14871312 [Szyjanowicz2004]
  20. Takahashi J, Rudsander UJ, Hedenström M, Banasiak A, Harholt J, Amelot N, Immerzeel P, Ryden P, Endo S, Ibatullin FM, Brumer H, del Campillo E, Master ER, Scheller HV, Sundberg B, Teeri TT, and Mellerowicz EJ. (2009). KORRIGAN1 and its aspen homolog PttCel9A1 decrease cellulose crystallinity in Arabidopsis stems. Plant Cell Physiol. 2009;50(6):1099-115. DOI:10.1093/pcp/pcp062 | PubMed ID:19398462 [Takahashi2009]
  21. Peng L, Kawagoe Y, Hogan P, and Delmer D. (2002). Sitosterol-beta-glucoside as primer for cellulose synthesis in plants. Science. 2002;295(5552):147-50. DOI:10.1126/science.1064281 | PubMed ID:11778054 [Peng2002]
  22. Rudsander UJ, Sandstrom C, Piens K, Master ER, Wilson DB, Brumer Iii H, Kenne L, and Teeri TT. (2008). Comparative NMR analysis of cellooligosaccharide hydrolysis by GH9 bacterial and plant endo-1,4-beta-glucanases. Biochemistry. 2008;47(18):5235-41. DOI:10.1021/bi702193e | PubMed ID:18402467 [Rudsander2008]
  23. Robert S, Bichet A, Grandjean O, Kierzkowski D, Satiat-Jeunemaître B, Pelletier S, Hauser MT, Höfte H, and Vernhettes S. (2005). An Arabidopsis endo-1,4-beta-D-glucanase involved in cellulose synthesis undergoes regulated intracellular cycling. Plant Cell. 2005;17(12):3378-89. DOI:10.1105/tpc.105.036228 | PubMed ID:16284310 [Robert2005]
  24. Vain T, Crowell EF, Timpano H, Biot E, Desprez T, Mansoori N, Trindade LM, Pagant S, Robert S, Höfte H, Gonneau M, and Vernhettes S. (2014). The Cellulase KORRIGAN Is Part of the Cellulose Synthase Complex. Plant Physiol. 2014;165(4):1521-1532. DOI:10.1104/pp.114.241216 | PubMed ID:24948829 [Vain2014]
  25. Lei L, Zhang T, Strasser R, Lee CM, Gonneau M, Mach L, Vernhettes S, Kim SH, J Cosgrove D, Li S, and Gu Y. (2014). The jiaoyao1 Mutant Is an Allele of korrigan1 That Abolishes Endoglucanase Activity and Affects the Organization of Both Cellulose Microfibrils and Microtubules in Arabidopsis. Plant Cell. 2014;26(6):2601-2616. DOI:10.1105/tpc.114.126193 | PubMed ID:24963054 [Lei2014]
  26. Brummell DA, Hall BD, and Bennett AB. (1999). Antisense suppression of tomato endo-1,4-beta-glucanase Cel2 mRNA accumulation increases the force required to break fruit abscission zones but does not affect fruit softening. Plant Mol Biol. 1999;40(4):615-22. DOI:10.1023/a:1006269031452 | PubMed ID:10480385 [Brummel1999]
  27. Brummell DA, Bird CR, Schuch W, and Bennett AB. (1997). An endo-1,4-beta-glucanase expressed at high levels in rapidly expanding tissues. Plant Mol Biol. 1997;33(1):87-95. DOI:10.1023/a:1005733213856 | PubMed ID:9037162 [Brummell1997]
  28. Kalaitzis P, Hong SB, Solomos T, and Tucker ML. (1999). Molecular characterization of a tomato endo-beta-1,4-glucanase gene expressed in mature pistils, abscission zones and fruit. Plant Cell Physiol. 1999;40(8):905-8. DOI:10.1093/oxfordjournals.pcp.a029621 | PubMed ID:10555309 [Kalaitzis1999]
  29. Shani Z, Dekel M, Tsabary G, and Shoseyov O. (1997). Cloning and characterization of elongation specific endo-1,4-beta-glucanase (cel1) from Arabidopsis thaliana. Plant Mol Biol. 1997;34(6):837-42. DOI:10.1023/a:1005849627301 | PubMed ID:9290636 [Shani1997]
  30. Catalá C, Rose JK, and Bennett AB. (1997). Auxin regulation and spatial localization of an endo-1,4-beta-D-glucanase and a xyloglucan endotransglycosylase in expanding tomato hypocotyls. Plant J. 1997;12(2):417-26. DOI:10.1046/j.1365-313x.1997.12020417.x | PubMed ID:9301092 [Catala1997]
  31. Harpster MH, Brummell DA, and Dunsmuir P. (1998). Expression analysis of a ripening-specific, auxin-repressed endo-1, 4-beta-glucanase gene in strawberry. Plant Physiol. 1998;118(4):1307-16. DOI:10.1104/pp.118.4.1307 | PubMed ID:9847104 [Brummell1998]
  32. Bonghi C, Rascio N, Ramina A, and Casadoro G. (1992). Cellulase and polygalacturonase involvement in the abscission of leaf and fruit explants of peach. Plant Mol Biol. 1992;20(5):839-48. DOI:10.1007/BF00027155 | PubMed ID:1281437 [Bonghi1998]
  33. Boraston AB, Bolam DN, Gilbert HJ, and Davies GJ. (2004). Carbohydrate-binding modules: fine-tuning polysaccharide recognition. Biochem J. 2004;382(Pt 3):769-81. DOI:10.1042/BJ20040892 | PubMed ID:15214846 [Boraston2004]
  34. Yoshida K, Imaizumi N, Kaneko S, Kawagoe Y, Tagiri A, Tanaka H, Nishitani K, and Komae K. (2006). Carbohydrate-binding module of a rice endo-beta-1,4-glycanase, OsCel9A, expressed in auxin-induced lateral root primordia, is post-translationally truncated. Plant Cell Physiol. 2006;47(11):1555-71. DOI:10.1093/pcp/pcl021 | PubMed ID:17056619 [YoshidaImaizumi2006]

All Medline abstracts: PubMed