title: Sucrose synthase activity in the sus1/sus2/sus3/sus4 Arabidopsis mutant is sufficient to support normal cellulose and starch production.
abstract: Sucrose synthase (SUS) catalyzes the reversible conversion of sucrose and a nucleoside diphosphate into the corresponding nucleoside diphosphate-glucose and fructose. In Arabidopsis, a multigene family encodes six SUS (SUS1-6) isoforms. The involvement of SUS in the synthesis of UDP-glucose and ADP-glucose linked to Arabidopsis cellulose and starch biosynthesis, respectively, has been questioned by Barratt et al. [(2009) Proc Natl Acad Sci USA 106:13124-13129], who showed that (i) SUS activity in wild type (WT) leaves is too low to account for normal rate of starch accumulation in Arabidopsis, and (ii) different organs of the sus1/sus2/sus3/sus4 SUS mutant impaired in SUS activity accumulate WT levels of ADP-glucose, UDP-glucose, cellulose and starch. However, these authors assayed SUS activity under unfavorable pH conditions for the reaction. By using favorable pH conditions for assaying SUS activity, in this work we show that SUS activity in the cleavage direction is sufficient to support normal rate of starch accumulation in WT leaves. We also demonstrate that sus1/sus2/sus3/sus4 leaves display WT SUS5 and SUS6 expression levels, whereas leaves of the sus5/sus6 mutant display WT SUS1-4 expression levels. Furthermore, we show that SUS activity in leaves and stems of the sus1/sus2/sus3/sus4 and sus5/sus6 plants is ∼85% of that of WT leaves, which can support normal cellulose and starch biosynthesis. The overall data disprove Barratt et al. (2009) claims, and are consistent with the possible involvement of SUS in cellulose and starch biosynthesis in Arabidopsis.
authors.affiliation: Instituto de Agrobiotecnología,  Universidad Pública de Navarra/Consejo Superior de Investigaciones Científicas/Gobierno de Navarra, 31192 Mutiloabeti, Nafarroa,  Spain.
authors.forename: Edurne
authors.initials: E
authors.lastname: Baroja-Fernández
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Muñoz
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Bahaji
authors.forename: Goizeder
authors.initials: G
authors.lastname: Almagro
authors.forename: Manuel
authors.initials: M
authors.lastname: Montero
authors.forename: Ed
authors.initials: E
authors.lastname: Etxeberria
authors.forename: Maite
authors.initials: M
authors.lastname: Hidalgo
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Sesma
authors.forename: Javier
authors.initials: J
authors.lastname: Pozueta-Romero
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D002482:Cellulose / Q000096:biosynthesis*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007700:Kinetics; D008027:Light; D015636:Magnesium Chloride / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D010936:Plant Extracts / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis*; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
chemical_list: D010936:Plant Extracts; D012333:RNA, Messenger; D011994:Recombinant Proteins; D015636:Magnesium Chloride; D000245:Adenosine Diphosphate Glucose; D002482:Cellulose; D013213:Starch; D005964:Glucosyltransferases; C022699:sucrose synthase; D014532:Uridine Diphosphate Glucose