[Molecular cloning and characterization of a novel DoSWEET1 gene from Dendrobium officinale]

SWEET (sugars will be eventually exported transporters) constitute a large and conserved gene family of sugar transporters in eukaryotes, which are important in the cellular metabolisms, growth and development, and plant-microbe interaction in plants. In the present study, a full length cDNA of SWEET encoding gene, designed as DoSWEET1 (GenBank accession No. KT957550), was identified in Dendrobium officinale using RT-PCR and RACE approaches. DoSWEET1 was 1 150 bp in length and encoded a 262-aa protein with a molecular weight of 29.18 kD and an isoelectric point of 9.49. The deduced DoSWEET1 protein contained seven transmembrane regions and two conserved MtN3-slv domains (11-94, 130-212）. Multiple sequence alignment revealed that DoSWEET1 had high identities 45%-54.6%） with SWEET proteins from various plants. A neighbor joining phylogenetic analysis suggests that DoSWEET1 belonged to the class Ⅱ subgroup of the SWEET evolutionary tree, and was closely related to rice OsSWEET13, OsSWEET14, and OsSWEET15. qPCR analysis demonstrated that DoSWEET1 gene was differentially expressed in the three included organs of D. officinale, and the expression was most abundant in the roots at 9.88 fold over that of the stems, followed by that of the leaves with 2.85 fold higher. In the 3rd symbiotic germinating seeds infected by Tulasnella sp., the transcipts were dramatically induced by 1 359.06 fold over that in the ungerniamted control seeds, suggesting a vital role of the gene in the D. officinale symbiotic germination process. Molecular cloning and characterization of the novel DoSWEET1 gene provides a foundation for the functional study of the gene in sugar translocation during the D. officinale symbiotic germination process.