Thaumatin-like proteins are differentially expressed and localized in phloem tissues of hybrid poplar.
BACKGROUND
Two thaumatin-like proteins (TLPs) were previously identified in phloem exudate of hybrid poplar (Populus trichocarpa x P. deltoides) using proteomics methods, and their sieve element localization confirmed by immunofluorescence. In the current study, we analyzed different tissues to further understand TLP expression and localization in poplar, and used immunogold labelling to determine intracellular localization.


RESULTS
Immunofluorescence using a TLP antiserum confirmed the presence of TLP in punctate, organelle-like structures within sieve elements. On western blots, the antiserum labeled two constitutively expressed proteins with distinct expression patterns. Immunogold labelling suggested that TLPs are associated with starch granules and starch-containing plastids in sieve elements and phloem parenchyma cells. In addition, the antiserum recognized TLPs in the inner cell wall and sieve plate region of sieve elements.


CONCLUSIONS
TLP localization in poplar cells and tissues is complex. TLP1 is expressed predominantly in tissues with a prominent vascular system such as midveins, petioles and stems, whereas the second TLP is primarily expressed in starch-storing plastids found in young leaves and the shoot apex.
Dafoe
Nicole J
NJ
Department of Biology, University of Victoria, Victoria, BC, Canada.
Gowen
Brent E
BE
Constabel
C Peter
CP
D000595:Amino Acid Sequence; D000818:Animals; D002678:Chimera; D008969:Molecular Sequence Data; D052585:Phloem / Q000737:chemistry / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D032107:Populus / Q000737:chemistry / Q000378:metabolism*; D040901:Proteomics / Q000379:methods
D010940:Plant Proteins; C003427:thaumatin protein, plant
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