title: Altered xylem-phloem transfer of amino acids affects metabolism and leads to increased seed yield and oil content in Arabidopsis.
abstract: Seed development and nitrogen (N) storage depend on delivery of amino acids to seed sinks. For efficient translocation to seeds, amino acids are loaded into the phloem in source leaves and along the long distance transport pathway through xylem-phloem transfer. We demonstrate that Arabidopsis thaliana AMINO ACID PERMEASE2 (AAP2) localizes to the phloem throughout the plant. AAP2 T-DNA insertion lines showed changes in source-sink translocation of amino acids and a decrease in the amount of seed total N and storage proteins, supporting AAP2 function in phloem loading and amino acid distribution to the embryo. Interestingly, in aap2 seeds, total carbon (C) levels were unchanged, while fatty acid levels were elevated. Moreover, branch and silique numbers per plant and seed yield were strongly increased. This suggests changes in N and C delivery to sinks and subsequent modulations of sink development and seed metabolism. This is supported by tracer experiments, expression studies of genes of N/C transport and metabolism in source and sink, and by phenotypic and metabolite analyses of aap2 plants. Thus, AAP2 is key for xylem to phloem transfer and sink N and C supply; moreover, modifications of N allocation can positively affect C assimilation and source-sink transport and benefit sink development and oil yield.
authors.affiliation: School of Biological Sciences, Center for Reproductive Biology, Washington State University, Pullman, Washington 99164-4236, USA.
authors.forename: Lizhi
authors.initials: L
authors.lastname: Zhang
authors.forename: Qiumin
authors.initials: Q
authors.lastname: Tan
authors.forename: Raymond
authors.initials: R
authors.lastname: Lee
authors.forename: Alexander
authors.initials: A
authors.lastname: Trethewy
authors.forename: Yong-Hwa
authors.initials: YH
authors.lastname: Lee
authors.forename: Mechthild
authors.initials: M
authors.lastname: Tegeder
mesh_terms: D026922:Amino Acid Transport Systems, Acidic / Q000235:genetics / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D017360:Arabidopsis / Q000737:chemistry* / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D002244:Carbon / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D019697:Onions / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D052585:Phloem / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D010938:Plant Oils / Q000737:chemistry / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000737:chemistry / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000737:chemistry / Q000378:metabolism; D052584:Xylem / Q000378:metabolism*
chemical_list: C420582:AAP2 protein, Arabidopsis; D026922:Amino Acid Transport Systems, Acidic; D000596:Amino Acids; D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D010938:Plant Oils; D011993:Recombinant Fusion Proteins; C036483:T-DNA; D002244:Carbon; D009584:Nitrogen