Increasing sucrose uptake capacity of wheat grains stimulates storage protein synthesis.
Increasing grain sink strength by improving assimilate uptake capacity could be a promising approach toward getting higher yield. The barley (Hordeum vulgare) sucrose transporter HvSUT1 (SUT) was expressed under control of the endosperm-specific Hordein B1 promoter (HO). Compared with the wild type, transgenic HOSUT grains take up more sucrose (Suc) in vitro, showing that the transgene is functional. Grain Suc levels are not altered, indicating that Suc fluxes are influenced rather than steady-state levels. HOSUT grains have increased percentages of total nitrogen and prolamins, which is reflected in increased levels of phenylalanine, tyrosine, tryptophan, isoleucine, and leucine at late grain development. Transcript profiling indicates specific stimulation of prolamin gene expression at the onset of storage phase. Changes in gene expression and metabolite levels related to carbon metabolism and amino acid biosynthesis suggest deregulated carbon-nitrogen balance, which together indicate carbon sufficiency and relative depletion of nitrogen. Genes, deregulated together with prolamin genes, might represent candidates, which respond positively to assimilate supply and are related to sugar-starch metabolism, cytokinin and brassinosteroid functions, cell proliferation, and sugar/abscisic acid signaling. Genes showing inverse expression patterns represent potential negative regulators. It is concluded that HvSUT1 overexpression increases grain protein content but also deregulates the metabolic status of wheat (Triticum aestivum) grains, accompanied by up-regulated gene expression of positive and negative regulators related to sugar signaling and assimilate supply. In HOSUT grains, alternating stimulation of positive and negative regulators causes oscillatory patterns of gene expression and highlights the capacity and great flexibility to adjust wheat grain storage metabolism in response to metabolic alterations.
Weichert
Nicola
N
Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung, D-06466 Gatersleben, Germany.
Saalbach
Isolde
I
Weichert
Heiko
H
Kohl
Stefan
S
Erban
Alexander
A
Kopka
Joachim
J
Hause
Bettina
B
Varshney
Alok
A
Sreenivasulu
Nese
N
Strickert
Marc
M
Kumlehn
Jochen
J
Weschke
Winfriede
W
Weber
Hans
H
D000040:Abscisic Acid / Q000032:analysis; D000596:Amino Acids / Q000096:biosynthesis; D002244:Carbon / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D055314:Seed Storage Proteins / Q000096:biosynthesis*; D012639:Seeds / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*; D014908:Triticum / Q000235:genetics / Q000378:metabolism*
D000596:Amino Acids; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D055314:Seed Storage Proteins; C078729:sucrose transport protein, plant; D013395:Sucrose; D000040:Abscisic Acid; D002244:Carbon