title: A novel strategy to produce sweeter tomato fruits with high sugar contents by fruit-specific expression of a single bZIP transcription factor gene.
abstract: Enhancement of sugar content and sweetness is desirable in some vegetables and in almost all fruits; however, biotechnological methods to increase sugar content are limited. Here, a completely novel methodological approach is presented that produces sweeter tomato fruits but does not have any negative effects on plant growth. Sucrose-induced repression of translation (SIRT), which is mediated by upstream open reading frames (uORFs), was initially reported in Arabidopsis AtbZIP11, a class S basic region leucine zipper (bZIP) transcription factor gene. Here, two AtbZIP11 orthologous genes, SlbZIP1 and SlbZIP2, were identified in tomato (Solanum lycopersicum). SlbZIP1 and SlbZIP2 contained four and three uORFs, respectively, in the cDNA 5'-leader regions. The second uORFs from the 5' cDNA end were conserved and involved in SIRT. Tomato plants were transformed with binary vectors in which only the main open reading frames (ORFs) of SlbZIP1 and SlbZIP2, without the SIRT-responsive uORFs, were placed under the control of the fruit-specific E8 promoter. Growth and morphology of the resulting transgenic tomato plants were comparable to those of wild-type plants. Transgenic fruits were approximately 1.5-fold higher in sugar content (sucrose/glucose/fructose) than nontransgenic tomato fruits. In addition, the levels of several amino acids, such as asparagine and glutamine, were higher in transgenic fruits than in wild-type fruits. This was expected because SlbZIP transactivates the asparagine synthase and proline dehydrogenase genes. This 'sweetening' technology is broadly applicable to other plants that utilize sucrose as a major translocation sugar.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan.
authors.forename: G H M
authors.initials: GH
authors.lastname: Sagor
authors.affiliation: Laboratory Center, Biodiversity and Climate Research Center, Frankfurt am Main, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Berberich
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Nishiyama
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kanayama
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan.|Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Muramoto
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Tomonobu
authors.initials: T
authors.lastname: Kusano
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D005638:Fruit / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D016366:Open Reading Frames; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D013395:Sucrose / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D050976:Basic-Leucine Zipper Transcription Factors; D010940:Plant Proteins; D005632:Fructose; D013395:Sucrose; D005947:Glucose
keywords: Solanum lycopersicum; basic region leucine zipper gene; deregulation of translational control; sucrose; sweetening technology; upstream open reading frame