title: Over-expression of AtEXLA2 alters etiolated arabidopsis hypocotyl growth.
abstract: OBJECTIVE
  Plant stature and shape are largely determined by cell elongation, a process that is strongly controlled at the level of the cell wall. This is associated with the presence of many cell wall proteins implicated in the elongation process. Several proteins and enzyme families have been suggested to be involved in the controlled weakening of the cell wall, and these include xyloglucan endotransglucosylases/hydrolases (XTHs), yieldins, lipid transfer proteins and expansins. Although expansins have been the subject of much research, the role and involvement of expansin-like genes/proteins remain mostly unclear. This study investigates the expression and function of AtEXLA2 (At4g38400), a member of the expansin-like A (EXLA) family in arabidposis, and considers its possible role in cell wall metabolism and growth.
  
  
  METHODS
  Transgenic plants of Arabidopsis thaliana were grown, and lines over-expressing AtEXLA2 were identified. Plants were grown in the dark, on media containing growth hormones or precursors, or were gravistimulated. Hypocotyls were studied using transmission electron microscopy and extensiometry. Histochemical GUS (β-glucuronidase) stainings were performed.
  
  
  RESULTS
  AtEXLA2 is one of the three EXLA members in arabidopsis. The protein lacks the typical domain responsible for expansin activity, but contains a presumed cellulose-interacting domain. Using promoter::GUS lines, the expression of AtEXLA2 was seen in germinating seedlings, hypocotyls, lateral root cap cells, columella cells and the central cylinder basally to the elongation zone of the root, and during different stages of lateral root development. Furthermore, promoter activity was detected in petioles, veins of leaves and filaments, and also in the peduncle of the flowers and in a zone just beneath the papillae. Over-expression of AtEXLA2 resulted in an increase of >10 % in the length of dark-grown hypocotyls and in slightly thicker walls in non-rapidly elongating etiolated hypocotyl cells. Biomechanical analysis by creep tests showed that AtEXLA2 over-expression may decrease the wall strength in arabidopsis hypocotyls.
  
  
  CONCLUSIONS
  It is concluded that AtEXLA2 may function as a positive regulator of cell elongation in the dark-grown hypocotyl of arabidopsis by possible interference with cellulose metabolism, deposition or its organization.
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia.
authors.forename: Agnieszka Karolina
authors.initials: AK
authors.lastname: Boron
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia.
authors.forename: Bram
authors.initials: B
authors.lastname: Van Loock
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Suslov
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia.
authors.forename: Marios Nektarios
authors.initials: MN
authors.lastname: Markakis
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Verbelen
authors.affiliation: Biology Department, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium and Saint-Petersburg State University, Faculty of Biology, Department of Plant Physiology and Biochemistry, Universitetskaya emb. 7/9, 199034 Saint-Petersburg, Russia kris.vissenberg@uantwerp.be.
authors.forename: Kris
authors.initials: K
authors.lastname: Vissenberg
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010802:Phylogeny; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; C000588566:EXLA2 protein, Arabidopsis
keywords: Arabidopsis thaliana; cell development; cell elongation; expansin-like; expansins; extensiometry; gravitropism; hypocotyl growth; plant cell wall