Comprehensive Metabolome and Transcriptome Analysis of Populus davidiana and Its Response to Drought Stress

Water is a primary element restricting the growth and survival of trees; thus, drought stress has a negative impact on plant development. In the current study, the transcriptional and metabolic changes in <i>Populus davidiana</i> were investigated under drought stress. We found that the chlorophyll content of poplars decreased, and reactive oxygen species (ROS) accumulation increased during drought stress. Following 2, 4, 6, 8, and 10 d of drought stress, 2127, 5334, 8894, 11,279, and 11,778 differentially expressed genes (DEGs) were identified, according to transcriptome analysis results. Enrichment analysis showed that a large number of DEGs were enriched in photosynthesis, chlorophyll decomposition and synthesis, and secondary metabolism-related pathways. The results of metabolomics analysis indicate that 131, 378, 334, 365, and 646 metabolites accumulated differentially following 2, 4, 6, 8, and 10 d, respectively, of drought stress. According to K-means clustering analysis, the contents of flavonoids significantly decreased alongside gene expression levels, while lipid content increased at 10 d of drought stress, alongside most of the related gene expression levels. Based on these data, two gene regulatory networks (GRNs) for lipid metabolism and flavonoid synthesis were constructed, each containing 45 transcription factors (TFs). Among them, six TFs (ERF39, GAI, ERF34, DOF5.2, DREB2A, and C3H6) were shared by two GRNs, suggesting that they may have diverse functions in response to drought stress. In summary, this study provides candidate genes for cultivating drought-resistant varieties and offers new insights into enhancing that resistance.