Genome-Wide Expression Profile of SOD Gene Family in Isatis indigotica and the Key Role of IiSOD2 and IiSOD7 in Alkaline Stress

Superoxide dismutase (SOD) is a key enzyme in the plant antioxidant system. It plays an essential role in plant adversity stress by scavenging excess reactive oxygen species to protect cells from oxidative damage. <i>Isatis indigotica</i>, being a mildly saline-tolerant plant, can be grown in soils containing a certain amount of saline-alkaline content. In order to reveal the <i>SOD</i> gene family members and their potential roles under saline and alkaline stress, the present study used a bioinformatics approach to identify 9 potential <i>IiSOD</i> genes in the <i>I. indigotica</i> genome. It analyzed the expression patterns of SOD family genes (<i>IiSODs</i>) in response to alkaline stress. According to the results of quantitative real-time PCR (qRT-PCR), the expression levels of the <i>IiSOD7</i> gene significantly increased within 120 h of alkaline stress treatment, while the expression level of the <i>IiSOD8</i> gene was the highest among all detected genes at 120 h of alkaline stress. The rest of the genes showed different degrees of expression. Alkaline stress showed significant and dynamic changes in the content of indigo and indirubin in leaves of <i>I. indigotica</i>. Finally, the yeast one-hybrid assay confirmed that <i>IiWRKY54</i> was able to activate the expression of <i>IiSOD2</i> and <i>IiSOD7</i>. Combined with qRT-PCR analysis, it was further hypothesized that <i>IiWRKY54</i> might enhance the alkaline tolerance of <i>I. indigotica</i> by regulating the expression of <i>IiSOD2</i> and <i>IiSOD7</i>. Taken together, this study lays the foundation for elucidating the function of the <i>IiSOD</i> gene in salinity stress tolerance of <i>I. indigotica</i> as well as promoting the genetic breeding of alkaline-tolerant varieties of <i>I. indigotica</i>.