Cloning and Expression Analysis of a Hemerocallis Fulva HfSWEET2a and Its Expression under Low Temperature Stress

Hemerocallis fulva is a well-known perennial flower in Chinese traditional flowers, which is widely used in family gardening, landscaping and other fields. Sugar is the main product of photosynthesis and the main energy source in plants. SWEET protein is a type of glycoefflux transporter found in recent years, which is involved in plant multiple physiological processes,including reproductive development, senescence and abiotic stress responses. In this study, Hemerocallis fulva SWEET2a gene was cloned from Hemerocallis fulva leaves by Quantitative Real-time PCR (qPCR), named HfSWEET2a (GenBank accession No. MT379659). Sequence analysis, homologous protein sequence alignment and phylogenetic tree analysis were carried out, and its expression at different temperatures was studied. The results of sequence analysis showed that HfSWEET2a gene contain a 690 bp ORF (open reading frame), encoding 229 amino acid residues. The results of physicochemical analysis showed that the molecular weight of HfSWEET2a is 25.531 kDa and the isoelectric point is 9.16. Subcellular localization showed that it is located in the Cell Membrane. HfSWEET2a has 7 typical transmembrane structures. The phylogenetic analysis of HfSWEET2a indicated that it has the closest relationship with asparagus, and pineapple was the second, with the similarity of 75.58% and 74.6%, respectively. The expression of HfSWEET2a gene was the highest at 0℃, the relative expression at 0℃ was 3.3 times of that at 15℃, 1.7 times of that at 10℃ and 3.7 times of that at 5℃. According to the research results, it was speculated that the HfSWEET2a gene of Hemerocallis fulva participated in the response to low temperature stress.