Overexpression of the <i>Arabidopsis</i> and winter squash superoxide dismutase genes enhances chilling tolerance via ABA-sensitive transcriptional regulation in transgenic <i>Arabidopsis</i>
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The winter squash (<i>Cucurbita moschata</i>, Cm) superoxide dismutase (SOD<i>) CmSOD</i> gene and <i>Arabidopsis thaliana</i> (<i>At</i>)<i>SOD</i> gene were transferred under a ubiquitin promoter into <i>Arabidopsis</i> via <i>Agrobacterium tumefaciens</i>. The expression and amount of SOD and the SOD activities in the <i>AtSOD</i> and <i>CmSOD</i> transgenic lines were significantly higher than those of non-transgenic (NT) plants exposed to 23 or 4°C treatment for 6 ~ 192-h periods. Furthermore, expressions of the cold-inducible gene (<i>AtCBF2</i>) and desiccation-responsible transcription factors (<i>AtRD</i>29A/B) were also activated in all transgenic lines compared to NT plants after chilling treatments. Compared to NT plants under chilling stress, superoxide (•O2<sup>−</sup>) accumulation was significantly lower, and chlorophyll (Chl) contents were significantly higher in all transgenic lines with higher SOD activity. Moreover, Arabidopsis seedlings overexpressing <i>AtSOD</i> and <i>CmSOD</i> also displayed greater resistance to chilling and less oxidative injury than NT plants under chilled conditions, indicating that the overexpression of <i>AtSOD</i> and <i>CmSOD</i> in Arabidopsis enhanced chilling tolerance by eliminating •O2<sup>−</sup>. The expression of <i>AtRD29A</i> was strongly up-regulated only in <i>AtSOD</i> transgenic plants treated with abscisic acid (ABA), while it was repressed in other transgenic plants, indicating ABA-sensitive <i>AtCBF2</i> and <i>AtRD29A/B</i> transcriptional regulation signaling pathways in transgenic <i>Arabidopsis</i> under chilling conditions.
