title: Antisense down-regulation of the strawberry β-galactosidase gene FaβGal4 increases cell wall galactose levels and reduces fruit softening.
abstract: Strawberry softening is characterized by an increase in the solubilization and depolymerization of pectins from cell walls. Galactose release from pectin side chains by β-galactosidase enzymes has been proposed as one reason for the increase in soluble pectins. A putative β-galactosidase gene, FaβGal4, has been identified using a custom-made oligonucleotide-based strawberry microarray platform. FaβGal4 was expressed mainly in the receptacle during fruit ripening, and was positively regulated by abscisic acid and negatively regulated by auxins. To ascertain the role of FaβGal4 in strawberry softening, transgenic plants containing an antisense sequence of this gene under the control of the CaMV35S promoter were generated. Phenotypic analyses were carried out in transgenic plants during three consecutive growing seasons, using non-transformed plants as control. Two out of nine independent transgenic lines yielded fruits that were 30% firmer than control at the ripe stage. FaβGal4 mRNA levels were reduced by 70% in ripe fruits from these selected transgenic lines, but they also showed significant silencing of FaβGal1, although the genes did not share significant similarity. These two transgenic lines also showed an increase in pectin covalently bound to the cell wall, extracted using Na2CO3. The amount of galactose in cell walls from transgenic fruits was 30% higher than in control; notably, the galactose increase was larger in the 1 M KOH fraction, which is enriched in hemicellulose. These results suggest that FaβGal4 participates in the solubilization of covalently bound pectins during ripening, reducing strawberry fruit firmness.
authors.affiliation: Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC), Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain.
authors.forename: Candelas
authors.initials: C
authors.lastname: Paniagua
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, 14071 Córdoba, Spain.
authors.forename: Rosario
authors.initials: R
authors.lastname: Blanco-Portales
authors.affiliation: IFAPA, Centro de Churriana, 29140 Málaga, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Barceló-Muñoz
authors.affiliation: Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC), Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: García-Gago
authors.affiliation: Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK.
authors.forename: Keith W
authors.initials: KW
authors.lastname: Waldron
authors.affiliation: Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Quesada
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, 14071 Córdoba, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Muñoz-Blanco
authors.affiliation: Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora" (IHSM-UMA-CSIC), Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain mercado@uma.es.
authors.forename: José A
authors.initials: JA
authors.lastname: Mercado
mesh_terms: D002241:Carbohydrates / Q000032:analysis; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D031985:Fragaria / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D005638:Fruit / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D005690:Galactose / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D010641:Phenotype; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D030821:Plants, Genetically Modified; D016372:RNA, Antisense / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017550:Spectroscopy, Fourier Transform Infrared; D014574:Uronic Acids / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D002241:Carbohydrates; D010937:Plant Growth Regulators; D016372:RNA, Antisense; D014574:Uronic Acids; D001616:beta-Galactosidase; D005690:Galactose
keywords: Fragaria × ananassa; cell wall; fruit ripening; fruit softening; pectins.; β-galactosidase