The complete coding cDNA sequence (4410 nt) of CsMRP4 was obtained through DNA-walking and 5′-RACE on the C. sinensis total cDNA. Its open reading frame was 1469 aa in length (Additional file 2: Figure S1 and Additional file 3: Figure S2). The Mr. of CsMRP4 was about 165.5 kDa and its pI was estimated to be 6.5. BLASTP was performed against the UniProtKB/Swiss-Prot database , which is a high-quality, manually annotated, and non-redundant protein database. Annotation information from NCBI non-redundant and UniProtKB/TrEMBL databases need to be further reviewed, since those contents were generated using in silico annotation or large-scale functional prediction. CsMRP4 is the closest to human MRP4 (HsMRP4) (UniProt ID: O15439) with an E-value of 5.3e-147 and identity of 44.2%, followed by HsMRP6 (UniProt ID: O95255) of 8.8e-89 and 38.4%, Mus musculus MRP3 (MmMRP3) (UniProt ID: B2RX12) of 5.1e-104 and 38.2%, and MmMRP5 (UniProt ID: Q9R1X5) of 2.9e-115 and 38.0%. CsMRP4 was significantly matched to multiple MRPs since the highest-scoring pairwise alignment was found predominantly in the NBD2 region, which is particularly conserved among ABC family transporters . As a subfamily of the ABC family of transporters, the MRP subfamily contains 12 members including MRP1-9, cystic fibrosis transmembrane conductance regulator (CFTR), sulfonylurea receptor 1 (SUR1), and SUR2 [9, 10]. The highest identity (39.0%) was observed between CsMRP4 and HsMRP4 in comparison with canonical human MRP/SUR/CFTR subfamily (Additional file 4: Table S2). Thus, this clone was designated as CsMRP4.