The strictosidine synthase-like (SSL) gene family is a small plant immune-regulated gene family that plays a critical role in plant resistance to biotic/abiotic stresses. To date, very little has been reported on the SSL gene in plants. In this study, a total of thirteen SSLs genes were identified from poplar, and these were classified into four subgroups based on multiple sequence alignment and phylogenetic tree analysis, and members of the same subgroup were found to have similar gene structures and motifs. The results of the collinearity analysis showed that poplar SSLs had more collinear genes in the woody plants Salix purpurea and Eucalyptus grandis. The promoter analysis revealed that the promoter region of PtrSSLs contains a large number of biotic/abiotic stress response elements. Subsequently, we examined the expression patterns of PtrSSLs following drought, salt, and leaf blight stress, using RT-qPCR to validate the response of PtrSSLs to biotic/abiotic stresses. In addition, the prediction of transcription factor (TF) regulatory networks identified several TFs, such as ATMYB46, ATMYB15, AGL20, STOP1, ATWRKY65, and so on, that may be induced in the expression of PtrSSLs in response to adversity stress. In conclusion, this study provides a solid basis for a functional analysis of the SSL gene family in response to biotic/abiotic stresses in poplar.

Drought and salinity are two major environmental factors that severely limit plant growth and development. MYB functions as a transcription factor that is crucial in how plants respond to stress from adverse conditions. In this study, we identified a gene encoding Populus simonii × P. nigra MYB (v-myb avian myeloblastosis viral oncogene homolog) transcription factor, whose transcription level was significantly induced under salt stress and osmotic stress. Subcellular localisation results showed PsnMYB30 was located in the nucleus. Yeast one-hybrid assay indicated the gene exhibited transcriptional activation activity and it can precisely bind to the G-box elements. Under normal growth conditions, there were no significant differences in physiological and biochemical indicators between wild-type and transgenic tobacco. However, under salt and drought stress, transgenic tobacco overexpressing PsnMYB30 exhibited superior root length and fresh weight compared to the wild-type (WT), with higher levels of SOD, POD, proline, and chlorophyll content, and significantly lower MDA and H₂O₂ content than the WT. These findings indicate that PsnMYB30 significantly enhances the salt tolerance and drought resistance of transgenic tobacco. These results indicate that PsnMYB30 is a key target gene for studying salt-tolerant and drought-resistant plants in genetic breeding.