Overexpression of MdEPF2 improves water use efficiency and reduces oxidative stress in tomato

Increasing drought frequency and diminishing groundwater resources are critical environmental constraints that seriously reduce global plant production. However, these limitations might be partially addressed by improving crop drought tolerance and water-use efficiency (WUE). We isolated an epidermal patterning factor (EPF), MdEPF2, from apple (Malus domestica). Transcript levels of that gene were higher after plants were treated with abscisic acid and drought. To investigate its function in drought tolerance, we ectopically expressed MdEPF2 in Solanum lycopersicum cultivar 'Micro-Tom'. When compared with the wild type (WT), stomatal density was significantly lower in the leaves from the transgenics, which enabled those plants to avoid dehydration. Under drought stress, transgenic plants had higher values for relative leaf water content, chlorophyll, photosynthetic rates, and WUE than did WT. The former also had lower accumulations of reactive oxygen species and malonyldialdehyde but greater activities of antioxidant enzymes, thereby leading to less oxidative damage. Our results suggested that MdEPF2 is a functional ortholog of EPF2 in Arabidopsis and can be potentially used in apple breeding to improve WUE and drought tolerance in this economically important fruit crop.