Overexpression of LcMYB90 Transcription Factor Enhances Drought and Salt Tolerance in Blue Honeysuckle (Lonicera caerulea L.) and Tobacco (Nicotiana tabacum L.)

The MYB family plays a vital role in regulating plant stress resistance. However, the MYB protein in blue honeysuckle remains largely unexplored. In this study, the <i>LcMYB90</i> gene from blue honeysuckle 'Lanjingling' was stably transformed into tobacco and transiently transformed into blue honeysuckle to characterize its function. Subcellular localization analysis revealed that the LcMYB90 protein is localized in the nucleus. Transgenic plants overexpressing <i>LcMYB90</i> exhibited enhanced growth performance and higher survival rates under drought and salt stress conditions. These plants also showed increased levels of proline and chlorophyll, along with elevated activities of catalase, peroxidase, and superoxide dismutase. Conversely, malondialdehyde content and relative conductivity were lower, indicating that <i>LcMYB90</i> enhances tolerance to drought and salt stress. Under salt treatment, genes induced by osmotic stress, such as <i>NHX1</i> (Na⁺/H⁺ antiporters 1) and <i>SOS1</i> (salt overly sensitive 1), as well as antioxidant defense system genes like <i>SOD</i> (superoxide dismutase) and <i>CAT1</i> (catalase 1), were more highly induced in overexpression lines compared to the wild type, supporting the hypothesis that <i>LcMYB90</i> promotes salt tolerance by enhancing osmotic stress resistance and antioxidant capacity. Simultaneously, the transcription levels of genes involved in the abscisic acid pathway, including <i>NCED1/2</i> (9-cis-epoxycarotenoid dioxygenase <i>1/2</i>, <i>PYL4/8</i> (pyrabactin resistance-Like 4/8), and <i>CBL1</i> (Calcineurin B-like protein 1), were increased under drought stress conditions in the overexpression lines. These results suggest that <i>LcMYB90</i> maintains cellular homeostasis by promoting the expression of stress-related genes and regulating osmotic and oxidative substances, thereby improving tolerance to drought and salt stress.