The aim of our research is to understand the molecular processes of plant nitrogen nutrition, with a focus on amino acid transport. We seek to understand how transport of amino acids contributes to nitrogen use efficiency and to optimization of plant growth. To accomplish this, we use a methodologically integrative approach, ranging from cell and molecular biology to ecophysiology.

Ulrika Ganetag 1150Nitrogen availability is considered a bottleneck for plant biomass production in terrestrial ecosystems. In addition, the demand for nitrogen in different parts of the plant varies during different stages of plant growth and development. Therefore, the ability to appropriately allocate and subsequently re-use nitrogen, together with nitrogen uptake, are the major determinants of nitrogen use efficiency, and hence for optimized plant growth. Being the major form of trans- ported nitrogen, amino acids are the currency of nitrogen within plants. There is therefore a complex network of transport of amino acids during plant growth and development, implying a demand for an intricate and well-orchestrated transport system. How this network is regulated to optimize nitrogen use efficiency in response to developmental and environmental cues during plant growth is at present not very well known. Besides being a key determinant for plant growth, nitrogen is also regarded as a major pollutant, resulting for example in changes in biodiversity. In addition, human perturbation of the global nitrogen cycle is the second largest driver of global climate change. Plant uptake of nitrogen from the soil and internal nitrogen fluxes are key processes in the global nitrogen cycle. Therefore, the molecular dissection of amino acid transport in plants has broad significance for our understanding of how nitrogen fluxes contribute to the overall plant nitrogen budget. This knowledge is also important from a more applied perspective, opening up new avenues to optimize nitrogen fertilization in both agriculture and forestry.

ganeteg_1 ganeteg_2
Arabidopsis plants deficient in the amino acid transporter LHT1 Arabidopsis plants deficient in the amino acid transporter AAP5 (upper left corner) are insensitive to toxic concentrations of arginine.

We have identified two candidate Arabidopsis amino acid transporters, LHT1 and AAP5, for involvement in root uptake of amino acids from the soil solution. The process of amino acid uptake in plants has been demonstrated both in laboratory and field settings, and has thus been well established. However, the ecological significance of organic Nitrogen uptake for plant nitrogen nutrition is still a matter of intense debate. One of our projects aims to resolve the molecular mechanisms and ecological significance of root amino acid uptake. To accomplish this we use a collection of transgenic Arabidopsis and Populus with different amino acid uptake profiles in our studies.
We also want to understand how the processes of nitrogen allocation and remobilization contribute to nitrogen use efficiency in plants. This work focuses on how amino acid transporters are orchestrated to allocate and redistribute nitrogen in response to developmental and environmental cues. Being mediated by a gene family comprised of 50 genes or more, the investigation of amino acid transport is a complex task (at least 53 and 90 genes have been annotated as putative amino acid/auxin permeases in the Arabidopsis and Populus genomes, respectively). It is believed that amino acid transporters are functionally separated by their substrate specificity and their temporal and spatial expression patterns. However, many amino acid transporters have been shown to have multiple functions in plants. Similarly, LHT1 has been identified as being involved in redistribution of amino acids in leaf mesophyll cells, besides its function in root amino acid uptake. We are investigating the role of LHT1 and a number of other key amino acid transporters in the allocation and remobilization of amino acids. Wild type and transgenic Populus are being analyzed with respect to, for example, gene expression, nutrient uptake, growth and nitrogen allocation, in response to developmental and environmental cues under controlled conditions and in the field.
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Publication list

  1. AtLHT1 Transporter Can Facilitate the Uptake and Translocation of a Glycinergic-Chlorantraniliprole Conjugate in Arabidopsis thaliana
    J Agric Food Chem. 2018, 66(47):12527-12535
  2. Nitrogen utilization during germination of somatic embryos of Norway spruce: revealing the importance of supplied glutamine for nitrogen metabolism
    Trees 2018, 33(2):383-394
    Carlsson J, Egertsdotter U, Ganeteg U, Svennerstam H

    Key message
    This paper shows that germinating Norway spruce somatic embryos are dependent on the carbon and nitrogen supplied in the medium, and that supplied glutamine accounts for 50 % of assimilated nitrogen during germination.

    The female megagametophyte, which provides the zygotic embryo with nitrogen (N), carbon (C) and energy during germination, is not present in Norway spruce (Picea abies) mature somatic embryos. Therefore, somatic embryos presumably rely on nutrients supplied in the germination medium in addition to their storage compounds accumulated during maturation. However, to what extent stored versus supplied compounds contribute to a somatic embryo germination is unclear. In this 24-day study, we addressed the above question by monitoring the biomass changes and the N and C budget during somatic embryo germination, under low-intensity red light. We found that the C and N storage reserves, accumulated during the maturation phase, were not sufficient to support the growth of the germinating somatic embryos, rather they were dependent on the medium components. In addition, in a previous study it has been found that glutamine (Gln) supplied in the medium was crucial for maintaining the primary amino acid (AA) metabolism and growth of the proliferating embryogenic cultures of Norway spruce (Carlsson et al., PLoS One 12(8):e0181785, 2017). Therefore, we hypothesised that Gln would be required as a significant source of N also during somatic embryo germination. By tracing the uptake of isotopically labelled N-sources from the medium and further into primary N assimilation, we found that Gln was the preferred source of N for the germinating somatic embryos, accounting for 50% of assimilated N. As the amounts of both arginine (Arg) and Gln were increased in the germinating somatic embryos, it also suggested that germination in low-intensity red light promoted N storage, similar to what has been observed in the zygotic embryo maturation in conifers (King, Gifford, Plant Physiol 113:1125–1135, 1997).

    e-link to publication
  3. Design of a New Glutamine-Fipronil Conjugate with alpha-Amino Acid Function and Its Uptake by A-thaliana Lysine Histidine Transporter 1 (AtLHT1)
  4. Nitrogen uptake and assimilation in proliferating embryogenic cultures of Norway spruce-Investigating the specific role of glutamine
    PLoS One. 2017, 12(8):e0181785 eCollection 2017
  5. Amino acid transporter mutants of Arabidopsis provides evidence that a non-mycorrhizal plant acquires organic nitrogen from agricultural soil
    Plant Cell Environ. 2017, 40(3):413-423
  6. Genomics in a changing arctic: critical questions await the molecular ecologist
    MOLECULAR ECOLOGY, 2015, 24(10):2301-2309
  7. Genetics of superior growth traits in trees are being mapped but will the faster-growing risk-takers make it in the wild?
    Tree Physiol. 2014, 34(11):1141-1148
  8. Exploring the nitrogen ingestion of aphids - a new method using electrical penetration graph and (15)n labelling
    PLoS One. 2013 Dec 23;8(12):e83085
  9. Cambui CA, Svennerstam H, Gruffman L, Nordin A, Ganeteg U, Näsholm T
    Patterns of plant biomass partitioning depend on nitrogen source
    PLoS one: 2011 6:e19211
  10. Svennerstam H, Jämtgård S, Ahmad I, Huss-Danell K, Näsholm T, Ganeteg U
    Transporters in Arabidopsis roots mediating uptake of amino acids at naturally occurring concentrations
    New Phytologist: 2011, 191:459-467
  11. Näsholm T, Kielland K, Ganeteg U
    Uptake of organic nitrogen by plants
    New Phytologist: 2009 182:31-48
  12. Svennerstam H, Ganeteg U, Näsholm T
    Root uptake of cationic amino acids by Arabidopsis depends on functional expression of amino acid permease 5
    New Phytologist: 2008 18:620-630
  13. Forsum O, Svennerstam H, Ganeteg U, Näsholm T
    Capacities and constraints of amino acid utilization in Arabidopsis
    New Phytologist: 2008 179:1058-1069
  14. Svennerstam H, Ganeteg U, Bellini C, Näsholm T
    Comprehensive screening of Arabidopsis mutants suggests the lysine histidine transporter 1 to be involved in plant uptake of amino acids
    Plant Physiology: 2007 145:1853-1860
  15. Ruban AV, Solovieva S, Lee PJ, Ilioaia C, Wentworth M, Ganeteg U, Klimmek F, Chow WS, Anderson JM, Jansson S, Horton P
    Plasticity in the composition of the light harvesting antenna of higher plants preserves structural integrity and biological function
    Journal Of Biological Chemistry: 2006 281:14981-14990
  16. Ihalainen JA, Klimmek F, Ganeteg U, van Stokkum IHM, van Grondelle R, Jansson S, Dekker JP
    Excitation energy trapping in photosystem I complexes depleted in Lhca1 and Lhca4
    FEBS Lett: 2005 579:4787-4791
  17. Klimmek F, Ganeteg U, Ihalainen JA, van Roon H, Jensen PE, Scheller HV, Dekker JP, Jansson S
    Structure of the higher plant light harvesting complex I: in vivo characterization and structural interdependence of the Lhca proteins
    Biochemistry: 2005 44:3065-3073
  18. Ganeteg U, Külheim C, Andersson J, Jansson S
    Is each light-harvesting complex protein important for plant fitness?
    Plant Physiol: 2004 134:502-509
  19. Ganeteg U, Klimmek F, Jansson S
    Lhca5--an LHC-type protein associated with photosystem I
    Plant Mol Biol: 2004 54:641-651
  20. Ganeteg U, Strand A, Gustafsson P, Jansson S
    The properties of the chlorophyll a/b-binding proteins Lhca2 and Lhca3 studied in vivo using antisense inhibition
    Plant Physiology: 2001 127:150-158