Molecular cloning and characterization of cDNAs of the superoxide dismutase gene family in the resurrection plant Haberlea rhodopensis

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Resurrection plants can tolerate almost complete water loss in their vegetative parts. The superoxide dismutases (SODs) are essential enzymes of defense against the oxidative damage caused by water stress. Here, we cloned and characterized cDNAs of the SOD gene family in the resurrection plant Haberlea rhodopensis. Seven full-length cDNAs, and their partial genomic clones, were obtained by combination of degenerate PCR, RT-PCR and RACE. The derived amino acid sequences exhibited a very high degree of similarity to cytosolic Cu,Zn-SODs (HrCSD2, HrCSD3), chloroplastic Cu,Zn-SODs (HrCSD5), other Cu,Zn-SODs (HrCSD4), Mn-SODs (HrMSD) and Fe-SODs (HrFSD). One cDNA turned out to be a pseudogene (HrCSD1). All identified SOD genes were found expressed at transcriptional level--the HrCSD2, HrCSD5, HrMSD and HrFSD were constitutively expressed in all organs, while the HrCSD3 and HrCSD4 were organ-specific. The transcripts of the housekeeping SOD genes were detected at significant levels even in air-dry leaves. The multigene SOD family of H. rhodopensis is the first studied SOD family amongst resurrection plant species. Our finding of well expressed SOD transcripts in fully dehydrated leaves correlates with retention of SOD activity, and with the ability of H. rhodopensis to revive upon rehydration. Because of the endemic relict nature of that species, our findings may help to further elucidate the evolutionary relationships among different SOD isoforms from distinct plant species.