Arabidopsis type I proton-pumping pyrophosphatase expresses strongly in phloem, where it is required for pyrophosphate metabolism and photosynthate partitioning

Plant Physiol. 2015 Apr;167(4):1541-53. doi: 10.1104/pp.114.254342. Epub 2015 Feb 13.


Phloem loading is a critical process in plant physiology. The potential of regulating the translocation of photoassimilates from source to sink tissues represents an opportunity to increase crop yield. Pyrophosphate homeostasis is crucial for normal phloem function in apoplasmic loaders. The involvement of Arabidopsis (Arabidopsis thaliana) type I proton-pumping pyrophosphatase (AVP1) in phloem loading was analyzed at genetic, histochemical, and physiological levels. A transcriptional AVP1 promoter::GUS fusion revealed phloem activity in source leaves. Ubiquitous AVP1 overexpression (35S::AVP1 cassette) enhanced shoot biomass, photoassimilate production and transport, rhizosphere acidification, and expression of sugar-induced root ion transporter genes (POTASSIUM TRANSPORTER2 [KUP2], NITRATE TRANSPORTER2.1 [NRT2.1], NRT2.4, and PHOSPHATE TRANSPORTER1.4 [PHT1.4]). Phloem-specific AVP1 overexpression (Commelina Yellow Mottle Virus promoter [pCOYMV]::AVP1) elicited similar phenotypes. By contrast, phloem-specific AVP1 knockdown (pCoYMV::RNAiAVP1) resulted in stunted seedlings in sucrose-deprived medium. We also present a promoter mutant avp1-2 (SALK046492) with a 70% reduction of expression that did not show severe growth impairment. Interestingly, AVP1 protein in this mutant is prominent in the phloem. Moreover, expression of an Escherichia coli-soluble pyrophosphatase in the phloem (pCoYMV::pyrophosphatase) of avp1-2 plants resulted in severe dwarf phenotype and abnormal leaf morphology. We conclude that the Proton-Pumping Pyrophosphatase AVP1 localized at the plasma membrane of the sieve element-companion cell complexes functions as a synthase, and that this activity is critical for the maintenance of pyrophosphate homeostasis required for phloem function.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Diphosphates / metabolism*
  • Gene Expression
  • Gene Expression Regulation, Plant*
  • Genes, Reporter
  • Homeostasis
  • Inorganic Pyrophosphatase / genetics
  • Inorganic Pyrophosphatase / metabolism*
  • Mutation
  • Organ Specificity
  • Phenotype
  • Phloem / enzymology
  • Phloem / genetics
  • Plant Leaves / enzymology
  • Plant Leaves / genetics
  • Plant Leaves / growth & development
  • Plant Roots / enzymology
  • Plant Roots / genetics
  • Plant Roots / growth & development
  • Plant Shoots / enzymology
  • Plant Shoots / genetics
  • Plant Shoots / growth & development
  • Plants, Genetically Modified
  • Promoter Regions, Genetic / genetics
  • Seedlings / enzymology
  • Seedlings / genetics
  • Seedlings / growth & development
  • Sucrose / metabolism


  • Arabidopsis Proteins
  • Diphosphates
  • diphosphoric acid
  • Sucrose
  • AVP1 protein, Arabidopsis
  • Inorganic Pyrophosphatase