Identification of Cadmium-responsive Kandelia obovata SOD family genes and response to Cd toxicity

Abstract Superoxide dismutase (SOD) plays a central function in the antioxidant systems of plants. Expression of SOD family members in plants is reciprocally regulated in response to various abiotic stresses as well as to moderate cadmium (Cd) stress. The mangrove plant, Kandelia obovata, has a high tolerance to Cd. Characterization of mechanisms that control expression of K. obovata SOD (KoSOD) genes in response to heavy metal stress would provide new insight into the physiological and genetic tolerance mechanisms of mangrove plants in contaminated estuaries. Here, seven KoSOD genes belonging to three phylogenetic clusters were identified from K. obovata, as were exon deletions, intron retention, and alternative polyadenylation events that generated diverse KoSOD gene transcripts. Phylogenetic analysis and expression pattern assays in different K. obovata tissues suggested that KoFSD2 and KoCSD3 could be critical for Cd stress responses. Furthermore, KoFSD2 and KoCSD3 overexpressed individually in Nicotiana benthamiana promoted root elongation and higher SOD activity after Cd treatment of transgenic plants relative to wild type plants. The KoFSD2 lines maintained lower O2·− and H2O2 levels under both control and high Cd conditions, whereas KoCSD3 transgenic lines had higher O2·− and H2O2 content in the presence of high Cd. Our findings provide novel insight into reactive oxygen metabolism and genetic mechanisms of K. obovata Cd tolerance in contaminated estuaries.