title: AAP1 regulates import of amino acids into developing Arabidopsis embryos.
abstract: The embryo of Arabidopsis seeds is symplasmically isolated from the surrounding seed coat and endosperm, and uptake of nutrients from the seed apoplast is required for embryo growth and storage reserve accumulation. With the aim of understanding the importance of nitrogen (N) uptake into developing embryos, we analysed two mutants of AAP1 (At1g58360), an amino acid transporter that was localized to Arabidopsis embryos. In mature and desiccated aap1 seeds the total N and carbon content was reduced while the total free amino acid levels were strongly increased. Separately analysed embryos and seed coats/endosperm of mature seeds showed that the elevated amounts in amino acids were caused by an accumulation in the seed coat/endosperm, demonstrating that a decrease in uptake of amino acids by the aap1 embryo affects the N pool in the seed coat/endosperm. Also, the number of protein bodies was increased in the aap1 endosperm, suggesting that the accumulation of free amino acids triggered protein synthesis. Analysis of seed storage compounds revealed that the total fatty acid content was unchanged in aap1 seeds, but storage protein levels were decreased. Expression analysis of genes of seed N transport, metabolism and storage was in agreement with the biochemical data. In addition, seed weight, as well as total silique and seed number, was reduced in the mutants. Together, these results demonstrate that seed protein synthesis and seed weight is dependent on N availability and that AAP1-mediated uptake of amino acids by the embryo is important for storage protein synthesis and seed yield.
authors.affiliation: School of Biological Sciences, Center for Reproductive Biology, Washington State University, Pullman, WA, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Sanders
authors.forename: Ray
authors.initials: R
authors.lastname: Collier
authors.forename: Alexander
authors.initials: A
authors.lastname: Trethewy
authors.forename: Grant
authors.initials: G
authors.lastname: Gould
authors.forename: Renate
authors.initials: R
authors.lastname: Sieker
authors.forename: Mechthild
authors.initials: M
authors.lastname: Tegeder
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis / Q000378:metabolism*; D017360:Arabidopsis / Q000196:embryology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002244:Carbon / Q000032:analysis; D009584:Nitrogen / Q000032:analysis; D012333:RNA, Messenger / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D012639:Seeds / Q000235:genetics / Q000254:growth & development
chemical_list: C420564:AAP1 protein, Arabidopsis; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D002244:Carbon; D009584:Nitrogen