In the present study,an M-type TRX gene,designated as DoTRXm1 (GenBank accession No.KC178573),was identified from a medicinally important orchid species Dendrobium officinale,using RT-PCR and RACE methods.Sequence analyses showed that the full length cDNA of DoTRXm1 was 850 bp and the 570 bp ORF encoded a 189 aa protein with a molecular weight of 20.32 kD and an isoelectric point of 9.44;The deduced DoTRXm1 protein contained a conserved therodoxin domain (87~187) and a catalytic site (106~124).Multiple sequence alignment demonstrated that DoTRXm1 was highly similar (53%~70%) to the M-type TRXs genes in plants.Phylogenetic analysis showed that DoTRXm1 was closely related to monocots including rice,maize,and sorghum,and belonged to the Ⅱ clade of plant M-type TRXs genes.Real time quantitative PCR (qRT-PCR) analysis revealed that DoTRXm1 was constitutively expressed in leaves,stems,and roots of D.officinale.The transcription level of DoTRXm1 in roots was the highest (5.63 fold higher than that of leaves),followed by that of stems (2.35 fold),and leaves.Molecular characterization of DoTRXm1 will be useful for further functional elucidation of the gene involving in the development,stress responses in D.officinale.