The ORF of CsGRN (GenBank KY855531) was 714 bp and the specific primers were as follows: forward 5′-CGC GGA TCC TGT AAA TAT AAC CAG ACT TG-3′ (BamH I) (Thermo Scientific, Waltham, USA), Reverse: 5′-TTA CTC GAG CGG AGC ACA GGT GTA GTG AT-3′ (Xhol I) (Thermo Scientific). The underlined bases indicated restrictions sites. cDNA was synthesised from total RNA, which was isolated from frozen C. sinensis adult tissues. The amplification conditions were 94 °C for 1 min, 55 °C for 1 min and 72 °C for 1 min for 30 cycles, plus 72 °C for 10 min. The purified PCR products were ligated into the pGEM-T-Easy vector (Promega, Madison, USA), followed by transformation into E. coli DH5α (Promega). The resulting plasmid DNA was digested with the appropriate restriction enzymes, ligated into the pET-28a (+) expression vector (Novagen, Darmstadt, Germany), and then transformed into E. coli BL21 (DE3) (Promega). Selected clones were grown and induced with 1 mM isopropyl-β-d-thiogalactoside (IPTG, Sigma, Guangzhou, China) at 20 °C for 12–18 h. The bacterial cells were collected by centrifugation and were sonicated on ice. The supernatant was collected, and recombinant protein was purified using the His-Bind Purification Kit (Novagen). The lysates of purified protein were subjected to 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The concentration of purified recombinant protein was determined by using the BCA protein assay kit (Novagen).