Two alternative splicing variants of maize HKT1;1 confer salt tolerance in transgenic tobacco plants

The high-affinity potassium transporter (HKT) genes have crucial roles in the regulation of sodium and potassium transportation in many species, however little is known about maize HKT genes. In this study, we obtained two alternative splicing transcripts of ZmHKT1;1 gene. One was named as ZmHKT1;1a which has the intact coding sequence, and the other was named as ZmHKT1;1b which has a deficiency of the third exon and a retention of the second intron. The phylogenic tree analysis showed that both translation products of ZmHKT1;1a and ZmHKT1;1b belong to group I HKT proteins which prefer for Na⁺ transport than other cations. ZmHKT1;1a and ZmHKT1;1b showed different response to stress treatment in maize. Overexpressing ZmHKT1;1a or ZmHKT1;1b in transgenic tobacco plants conferred high salt tolerance by increasing root length and fresh weight of plants. When treated with high concentration of salt, transgenic tobacco plants manifested a trend of reduced Na⁺ content and increased K⁺ content in both shoot and root, suggesting that ZmHKT1;1 may involve in Na⁺ unloading and indirectly affect other transporter activity. It was also found that overexpression of ZmHKT1;1a and ZmHKT1;1b caused different expression of stress-related genes. The results in this study indicate that two alternative splicing variants of ZmHKT1;1 might be useful for the development of salt-tolerant transgenic crops.