Over-expression of the Salix matsudana expansin gene SmEXPA23 enhances plant salt tolerance

As a cell-wall relaxation protein, expansin plays an important role in plant stress-resistance processes. The Salix matsudana expansin gene EXPA23 in the salt-tolerant willow variety 9901 was highly expressed, being 1.83 times the level in the salt-sensitive willow variety Yanjiang, at fourth day after a 200 mM NaCl treatment, as determined by RT-PCR. The gene was cloned from 9901 and transformed into tobacco. In the salt-tolerance evaluation, the wild-type lines wilted severely after 4 days of a 200-mM salt stress, whereas the transgenic lines displayed better. And, the relative electrolyte leakage and malondialdehyde content of the transgenic lines were reduced by 9.87% and 19.26%, respectively, in comparison with those of the wild-type. Thus, SmEXPA23 over-expression greatly increased the salt tolerance of the plants. The results expand our knowledge of expansin's role in plant resistance and provide some new insights into the salt-tolerance mechanisms of willow. Key message Over-expressing an expansin gene SmEXPA23 from the salt tolerant willow variety 9901 in tobacco plants showed enhanced salt tolerance that would extend our understanding of the salt tolerance mechanism and be an important gene resource for plant molecular breeding.