Overexpression of a ‘Paulownia fortunei’ MYB Factor Gene, PfMYB44, Increases Salt and Drought Tolerance in Arabidopsis thaliana

<i>Paulownia fortunei (Seem.) Hemsl</i> is a <i>Paulownia</i> Sieb.et tree of the family Scrophulariaceae. It has become an important short-to-medium-term fast-growing multi-purpose tree species in China due to its rapid growth, strong adaptability, and excellent material properties. MYB transcription factors in plants have numerous and diverse functions, playing important roles in various aspects such as plant stress response. To investigate the function of MYB transcription factors in <i>Paulownia fortunei</i>, this study used PCR technology to clone the <i>PfMYB44</i> gene from <i>Paulownia fortunei</i>. The homology of PfMYB44 and SiMYB44 (<i>Sesamum indicum</i>) was the highest. Expression analysis results showed that <i>PfMYB44</i> was expressed in the root, stem, young leaf, and mature leaf of <i>Paulownia fortunei</i>, with the highest content in the root. Cold, drought, hot, salt, and ABA treatments could increase the expression level of <i>PfMYB44</i>. Overexpression-<i>PfMYB44</i> plants were constructed, and physiological and molecular analysis showed that <i>PfMYB44</i> could positively regulate salt and drought stresses. Under drought stress, the expression levels of <i>AtP5CS</i>, <i>AtCAT1</i>, <i>AtNCED3</i> and <i>AtSnRK2.4</i> in transgenic lines were significantly induced. Salt stress induced the expression of <i>AtNHX1</i>, <i>AtSOS1</i>, <i>AtSOS2</i> and <i>AtSOS3</i> genes, and the relative expression levels of these genes in transgenic <i>Arabidopsis</i> were higher. In conclusion, the functional study of <i>PfMYB44</i> laid a certain foundation for the study of <i>Paulownia</i> stress resistance, and was helpful to the study of its stress resistance mechanism and the cultivation of new stress resistance varieties.