A novel type of thioredoxin dedicated to symbiosis in legumes.
Thioredoxins (Trxs) constitute a family of small proteins in plants. This family has been extensively characterized in Arabidopsis (Arabidopsis thaliana), which contains six different Trx types: f, m, x, and y in chloroplasts, o in mitochondria, and h mainly in cytosol. A detailed study of this family in the model legume Medicago truncatula, realized here, has established the existence of two isoforms that do not belong to any of the types previously described. As no possible orthologs were further found in either rice (Oryza sativa) or poplar (Populus spp.), these novel isoforms may be specific for legumes. Nevertheless, on the basis of protein sequence and gene structure, they are both related to Trxs m and probably have evolved from Trxs m after the divergence of the higher plant families. They have redox potential values similar to those of the classical Trxs, and one of them can act as a substrate for the M. truncatula NADP-Trx reductase A. However, they differ from classical Trxs in that they possess an atypical putative catalytic site and lack disulfide reductase activity with insulin. Another important feature is the presence in both proteins of an N-terminal extension containing a putative signal peptide that targets them to the endoplasmic reticulum, as demonstrated by their transient expression in fusion with the green fluorescent protein in M. truncatula or Nicotiana benthamiana leaves. According to their pattern of expression, these novel isoforms function specifically in symbiotic interactions in legumes. They were therefore given the name of Trxs s, s for symbiosis.
Alkhalfioui
Fatima
F
Physiologie Moléculaire des Semences, UMR 1191 Université d'Angers-Institut National d'Horticulture-INRA, IFR 149 QUASAV, ARES, 49045 Angers cedex 01, France.
Renard
Michelle
M
Frendo
Pierre
P
Keichinger
Corinne
C
Meyer
Yves
Y
Gelhaye
Eric
E
Hirasawa
Masakazu
M
Knaff
David B
DB
Ritzenthaler
Christophe
C
Montrichard
Françoise
F
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D046913:Medicago truncatula / Q000502:physiology*; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D011817:Rabbits; D013559:Symbiosis; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism; D013879:Thioredoxins / Q000502:physiology*
D000906:Antibodies; D020033:Protein Isoforms; D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase