NtMYB12 Positively Regulates Flavonol Biosynthesis and Enhances Tolerance to Low Pi Stress in Nicotiana tabacum

Abstract

Phosphorus (P) is an essential macronutrient for plant growth and development. The concentration of flavonol, a natural plant antioxidant, is closely related to phosphorus nutritional status. However, the regulatory networks of flavonol biosynthesis under low Pi stress are still unclear. In this study, we identified a PFG-type MYB gene, <i>NtMYB12</i>, whose expression was significantly up-regulated under low Pi conditions. Overexpression of <i>NtMYB12</i> dramatically increased flavonol concentration and the expression of certain flavonol biosynthetic genes (<i>NtCHS</i>, <i>NtCHI</i>, and <i>NtFLS</i>) in transgenic tobacco. Moreover, overexpression of <i>NtMYB12</i> also increased the total P concentration and enhanced tobacco tolerance of low Pi stress by increasing the expression of <i>Pht1</i>-family genes (<i>NtPT1</i> and <i>NtPT2</i>). We further demonstrated that <i>NtCHS-</i>overexpressing plants and <i>NtPT2-</i>overexpressing plants also had increased flavonol and P accumulation and higher tolerance to low Pi stress, showing a similar phenotype to <i>NtMYB12</i>-overexpressing transgenic tobacco under low Pi stress. These results suggested that tobacco <i>NtMYB12</i> acts as a phosphorus starvation response enhancement factor and regulates <i>NtCHS</i> and <i>NtPT2</i> expression, which results in increased flavonol and P accumulation and enhances tolerance to low Pi stress.