Over-expression of the water and salt stress-regulated Asr1 gene confers an increased salt tolerance

ASR1 is a plant-specific, highly charged, low molecular weight polypeplide. Purified ASR1 was shown to posses sequence specific Zn²⁺-dependent DNA binding activity (Kalifa et al. Biochemical Journal 381, 373-378, 2004). Steady-state levels of tomato Asr1 mRNA and protein are transiently increased following exposure of plants to polyethylene glycol, NaCl or abscisic acid. The biological role of ASR1 could not be deduced from sequence analyses or sequence homologies. Tobacco plants over-expressing tomato ASR1 have a decreased rate of water loss and improved salt tolerance. Upon exposure to salt, ASR1-over-expressing plants accumulate less Na⁺ and proline than wild-type plants, and also results in increased steady-state levels of other gene products under non-stressed plant growth conditions. Therefore, ASR1 is probably involved in the regulation of water- or salt-stress-modulated gene expression.