title: Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene.
abstract: BACKGROUND
  AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink to source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones.
  
  
  RESULTS
  To assess the importance of this regulation to whole-plant growth and carbon partitioning, AtSUC2 cDNA was expressed from two exotic, phloem-specific promoters in a mutant background debilitated for AtSUC2 function. The first was a promoter element from Commelina Yellow Mottle Virus (CoYMV), and the second was the rolC promoter from Agrobacterium rhizogenes. CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation.
  
  
  CONCLUSIONS
  Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport. Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the endogenous sucrose/proton symporter genes has implications for biotechnology.
authors.affiliation: University of North Texas, Department of Biological Sciences, PO Box 305220, Denton, TX 76203-5220, USA. acsrivastava@noble.org
authors.forename: Avinash C
authors.initials: AC
authors.lastname: Srivastava
authors.forename: Savita
authors.initials: S
authors.lastname: Ganesan
authors.forename: Ihab O
authors.initials: IO
authors.lastname: Ismail
authors.forename: Brian G
authors.initials: BG
authors.lastname: Ayre
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D052585:Phloem / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D013395:Sucrose / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018076:DNA, Complementary; D018744:DNA, Plant; D026901:Membrane Transport Proteins; D010940:Plant Proteins; C036483:T-DNA; C078729:sucrose transport protein, plant; D013395:Sucrose; D002244:Carbon