LcMYB5, an R2R3-MYB family gene from Lonicera caerulea L., enhances drought and salt tolerance in transgenic tobacco and blue honeysuckle.

MYB transcription factors exert crucial functions in enhancing plant stress tolerance, which is impacted by soil drought and salinity. In our study, the R2R3-type MYB transcription factor gene LcMYB5 from blue honeysuckle (Lonicera caerulea L.) was successfully cloned and identified, and confirmed its nuclear localization. LcMYB5 overexpression was vastly enhanced drought and salt tolerance in both blue honeysuckle and tobacco seedlings. After drought stress, transgenic tobacco exhibited an average survival rate of 70.30%, while most wild-type (WT) plants perished, resulting in a survival rate of only 15.33%. Following salt stress, the average survival rate for transgenic tobacco reached 77.24%, compared to just 22.47% for WT plants. Measurements indicated, that transgenic tobacco had higher proline content than WT, as well as higher superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity. Transgenic tobacco decreased chlorophyll content less dramatically than WT tobacco, despite both tobaccos having decreased chlorophyll content. Furthermore, the level of malondialdehyde (MDA) and relative conductivity were lower in transgenic tobacco compared to WT. Furthermore, LcMYB5 overexpression significantly increased the expression levels of key genes related to drought stress (NCED1, NCED2, PYL4, PYL8, and CBL1) and salt stress (NHX1, SOD, CAT1, SOS1, and HSP17.8), thus improving transgenic tobacco's stress tolerance. Compared to WT blue honeysuckle, transiently transformed LcMYB5-expressing blue honeysuckle exhibited milder damage under stress conditions, a significant increase in chlorophyll and proline content was observed, the activities of SOD, POD and CAT were also significantly increased, the increase in MDA content and relative conductivity is relatively small. Additionally, In addition, transient expression of LcMYB5 can also positively regulate the expression of these five key genes of drought stress and five key genes of salt stress, so as to improve the resistance of transgenic blue honeysuckle to drought and salt stress. In summary, our study reveals the important regulatory role of LcMYB5 in plant resistance to drought and salt stress, providing theoretical support and potential application value for further improving crop stress resistance.