TY - JOUR
T1 - Arabidopsis thaliana ASN2 encoding asparagine synthetase is involved in the control of nitrogen assimilation and export during vegetative growth
AU - Gaufichon, Laure
AU - Masclaux-Daubresse, Céline
AU - Tcherkez, Guillaume
AU - Reisdorf-Cren, Michèle
AU - Sakakibara, Yukiko
AU - Hase, Toshiharu
AU - Clément, Gilles
AU - Avice, Jean Christophe
AU - Grandjean, Olivier
AU - Marmagne, Anne
AU - Boutet-Mercey, Stéphanie
AU - Azzopardi, Marianne
AU - Soulay, Fabienne
AU - Suzuki, Akira
PY - 2013/2
Y1 - 2013/2
N2 - We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2-1 knockout and asn2-2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO2 assimilation was not significantly different between lines under both 21 and 2% O2. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered 15N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant.
AB - We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2-1 knockout and asn2-2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO2 assimilation was not significantly different between lines under both 21 and 2% O2. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered 15N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant.
KW - Amino acid synthesis and metabolism
KW - Cellular localization
KW - Nitrogen assimilation and translocation
KW - Reverse genetics
UR - http://www.scopus.com/inward/record.url?scp=84871925879&partnerID=8YFLogxK
U2 - 10.1111/j.1365-3040.2012.02576.x
DO - 10.1111/j.1365-3040.2012.02576.x
M3 - Article
SN - 0140-7791
VL - 36
SP - 328
EP - 342
JO - Plant, Cell and Environment
JF - Plant, Cell and Environment
IS - 2
ER -