Calcium-dependent protein kinases (CDPKs) play an important regulatory role in the plant- arbuscular mycorrhiza/rhizobium nodule symbiosis.  However, the biological action of CDPKs in orchid mycorrhiza (OM) symbiosis remains unclear.  In the present study, a CDPK encoding gene, designated as DoCPK1 (GenBank accession No. JX193703), was identified from D. officinale roots infected by an OM fungus-Mycena sp. using the reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods, for the first time.  The full length cDNA of DoCPK1 was 2 137 bp in length and encoded a 534 aa protein with a molecular weight of 59.61 kD and an isoelectric point (pI) of 6.03.  The deduced DoCPK1 protein contained the conserved serine/threonine-protein kinase catalytic domain and four Ca²⁺ binding EF hand motifs.  Multiple sequence alignment demonstrated that DoCPK1 was highly homologous (85%) to the Panax ginseng PgCPK1 (ACY78680), followed by CDPKs genes from wheat, rice, and Arabidopsis (ABD98803, ADM14342, Q9ZSA2, respectively).  Phylogenetic analysis showed that DoCPK1 was closely related to CDPKs genes from monocots, such as wheat, maize and rice.  Real time quantitative PCR (qPCR) analysis revealed that DoCPK1 was constitutively expressed in the included tissues and the transcript levels were in the order of roots > stems > seeds > leaves.  Furthermore, DoCPK1 transcripts were significantly accumulated in roots 30 d after fungal infection, with 5.16 fold compared to that of the mock roots, indicating involvement of DoCPK1 during the early interaction between D. officinale and Mycena sp., and a possible role in the symbiosis process.  This study firstly provided important clues of a CDPK gene associated with OM symbiosis, and will be useful for further functional determination of the gene involving in D. officinale and Mycena sp. symbiosis.