Potential involvement of drought-induced Ran GTPase <i>CLRan1</i> in root growth enhancement in a xerophyte wild watermelon

Enhanced root growth is known as the survival strategy of plants under drought. Previous proteome analysis in drought-resistant wild watermelon has shown that Ran GTPase, an essential regulator of cell division and proliferation, was induced in the roots under drought. In this study, two cDNAs were isolated from wild watermelon, <i>CLRan1</i> and <i>CLRan2</i>, which showed a high degree of structural similarity with those of other plant Ran GTPases. Quantitative RT-PCR and promoter-GUS assays suggested that <i>CLRan1</i> was expressed mainly in the root apex and lateral root primordia, whereas <i>CLRan2</i> was more broadly expressed in other part of the roots. Immunoblotting analysis confirmed that the abundance of CLRan proteins was elevated in the root apex region under drought stress. Transgenic Arabidopsis overexpressing CLRan1 showed enhanced primary root growth, and the growth was maintained under osmotic stress, indicating that <i>CLRan1</i> functions as a positive factor for maintaining root growth under stress conditions. Ran GTPase (CLRan1), which is expressed in the roots of drought-resistant wild watermelon, functions as a positive factor for maintaining root growth under osmotic stress.