title: Silencing of the tomato sugar partitioning affecting protein (SPA) modifies sink strength through a shift in leaf sugar metabolism.
abstract: Limitations in our understanding about the mechanisms that underlie source-sink assimilate partitioning are increasingly becoming a major hurdle for crop yield enhancement via metabolic engineering. By means of a comprehensive approach, this work reports the functional characterization of a DnaJ chaperone related-protein (named as SPA; sugar partition-affecting) that is involved in assimilate partitioning in tomato plants. SPA protein was found to be targeted to the chloroplast thylakoid membranes. SPA-RNAi tomato plants produced more and heavier fruits compared with controls, thus resulting in a considerable increment in harvest index. The transgenic plants also displayed increased pigment levels and reduced sucrose, glucose and fructose contents in leaves. Detailed metabolic and enzymatic activities analyses showed that sugar phosphate intermediates were increased while the activity of phosphoglucomutase, sugar kinases and invertases was reduced in the photosynthetic organs of the silenced plants. These changes would be anticipated to promote carbon export from foliar tissues. The combined results suggested that the tomato SPA protein plays an important role in plastid metabolism and mediates the source-sink relationships by affecting the rate of carbon translocation to fruits.
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, 277, São Paulo, 05508-900, SP, Brazil; Instituto de Biotecnología, Instituto Nacional de Tecnología Agropecuaria (IB-INTA), PO Box 25, Castelar, B1712WAA, Argentina.
authors.forename: Luisa
authors.initials: L
authors.lastname: Bermúdez
authors.forename: Fabiana
authors.initials: F
authors.lastname: de Godoy
authors.forename: Pierre
authors.initials: P
authors.lastname: Baldet
authors.forename: Diego
authors.initials: D
authors.lastname: Demarco
authors.forename: Sonia
authors.initials: S
authors.lastname: Osorio
authors.forename: Leandro
authors.initials: L
authors.lastname: Quadrana
authors.forename: Juliana
authors.initials: J
authors.lastname: Almeida
authors.forename: Ramón
authors.initials: R
authors.lastname: Asis
authors.forename: Yves
authors.initials: Y
authors.lastname: Gibon
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.forename: Magdalena
authors.initials: M
authors.lastname: Rossi
authors.forename: Fernando
authors.initials: F
authors.lastname: Carrari
mesh_terms: D050260:Carbohydrate Metabolism; D020868:Gene Silencing; D006601:Hexoses / Q000378:metabolism; D018551:Solanum lycopersicum / Q000378:metabolism*; D010733:Phosphoglucomutase / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D010788:Photosynthesis; D010802:Phylogeny; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D014306:Trioses / Q000378:metabolism; D043324:beta-Fructofuranosidase / Q000378:metabolism
chemical_list: D006601:Hexoses; D010860:Pigments, Biological; D010940:Plant Proteins; D014306:Trioses; D010770:Phosphotransferases; D043324:beta-Fructofuranosidase; D010733:Phosphoglucomutase
keywords: chloroplast metabolism; fruit metabolism; small plastidial protein; source-sink partitioning; tomato