Abstract：Sugarcane (Saccharum species hybrid) is the most important crop for the production of sugar. Due to its high biomass production and lengthy growing season, sugarcane needs to absorb a large amount of potassium (K) throughout its life cycle. In the southern China where sugarcane is cultivated, most of the soil have low content of available K, which limits the production of sugarcane. To improve the productivity, one of the efficient means is to improve sugarcane cultivars that have efficient uptake capacity of K and hence are tolerant to low K. This study was conducted in which a major commercial cultivar, ROC22, was subject to low K stress. From the experiment, a potassium transporter gene, named SsHAK2 (GenBank accession number: KM98738), was cloned by reverse transcription-polymerase chainreaction (RT-PCR) from total RNA of sugarcane roots. The full length of the SsHAK2 gene was 2 798 bp, and contained a complete open reading frame of 2 352 bp encoding a protein with 784 amino acids. The molecular weight of SsHAK2 was 87.602 kD and the isoelectric point of 8.85, as the alkaline protein. It contained twelve transmembrane segmentand(S1~S12) and the possibility of subcellular localization in plasma membrane was 80%. The deduced polypeptide of SsHAK2 had three transmembrane domains, including potassium transporter domain and amino acid transporter domain. The homology analysis indicated that SsHAK2 shared sequence homology with other members of HAK family in plant, such as Zea mays, Oryza sativa, Hordeum vulgare, with the level of sequence identity ranging from 52% to 95%. The changes in expression of SsHAK2 under low K, drought and salt stresses were detected by qPCR analysis. Under low K stress condition, the gene had the highest inducible expression level at 96 hours, which was 1.70-fold than that of control. Under salt stress, the expression level began to increase rapidly after 48 hours stress of salt and also reached the highest at 96 hours or 4.37-fold than that of control. Under drought stress, the gene had the highest level at 12 hours or 4.07-fold than that of control, and then dropped to 1.69-fold at 24 hours. Afterwards from 24 to 48 hours, it was up-regulated and after 48 hours became down-regulated rapidly, by 96 hours which had the lowest inducible expression level or only 1/4 of that in control. It suggests that SsHAK2 might take part in responses to various stress in addition to low K. This study has established a foundation for future research on understanding the molecular mechanism of K uptake in sugarcane.
