title: Fasciclin-like arabinogalactan proteins: specialization for stem biomechanics and cell wall architecture in Arabidopsis and Eucalyptus.
abstract: The ancient cell adhesion fasciclin (FAS) domain is found in bacteria, fungi, algae, insects and animals, and occurs in a large family of fasciclin-like arabinogalactan proteins (FLAs) in higher plants. Functional roles for FAS-containing proteins have been determined for insects, algae and vertebrates; however, the biological functions of the various higher-plant FLAs are not clear. Expression of some FLAs has been correlated with the onset of secondary-wall cellulose synthesis in Arabidopsis stems, and also with wood formation in the stems and branches of trees, suggesting a biological role in plant stems. We examined whether FLAs contribute to plant stem biomechanics. Using phylogenetic, transcript abundance and promoter-GUS fusion analyses, we identified a conserved subset of single FAS domain FLAs (group A FLAs) in Eucalyptus and Arabidopsis that have specific and high transcript abundance in stems, particularly in stem cells undergoing secondary-wall deposition, and that the phylogenetic conservation appears to extend to other dicots and monocots. Gene-function analyses revealed that Arabidopsis T-DNA knockout double mutant stems had altered stem biomechanics with reduced tensile strength and a reduced tensile modulus of elasticity, as well as altered cell-wall architecture and composition, with increased cellulose microfibril angle and reduced arabinose, galactose and cellulose content. Using materials engineering concepts, we relate the effects of these FLAs on cell-wall composition with stem biomechanics. Our results suggest that a subset of single FAS domain FLAs contributes to plant stem strength by affecting cellulose deposition, and to the stem modulus of elasticity by affecting the integrity of the cell-wall matrix.
authors.affiliation: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia. colleen.macmillan@csiro.au
authors.forename: Colleen P
authors.initials: CP
authors.lastname: MacMillan
authors.forename: Shawn D
authors.initials: SD
authors.lastname: Mansfield
authors.forename: Zbigniew H
authors.initials: ZH
authors.lastname: Stachurski
authors.forename: Rob
authors.initials: R
authors.lastname: Evans
authors.forename: Simon G
authors.initials: SG
authors.lastname: Southerton
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D055119:Elastic Modulus; D005052:Eucalyptus / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D008031:Lignin / Q000378:metabolism; D009088:Mucoproteins / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018547:Plant Stems / Q000254:growth & development*; D013718:Tensile Strength
chemical_list: D004269:DNA, Bacterial; D009088:Mucoproteins; D010940:Plant Proteins; C036483:T-DNA; C006619:arabinogalactan proteins; D008031:Lignin