Transcriptome and Metabolome Conjoint Analysis Revealed that PaGLK Affects Photosynthesis and Composition of Root Exudates in Poplar

Photosynthetic carbon fixation is the main source of root exudates. GOLDEN2-LIKE (GLK) genes play an important role in photosynthetic carbon fixation. The root exudates mainly come from photosynthetic carbon. However, the relationship between GLK genes, root exudates, and photosynthetic carbon fixation and how photosynthesis affects root exudate in poplar are not clear. In this study, we performed comparative transcriptome and metabolome analyses of overexpression and expression-inhibited transgenic poplar. GO enrichment analysis showed that the downregulation of differentially expressed genes (DEGs) in expression-inhibited lines was related to photosynthesis in biological processes. Specifically, photosynthesis-antenna proteins, porphyrin and chlorophyll metabolism, and photosynthesis were significantly enriched in KEGG pathways. Gene expression showed consistent trends in qPCR and transcriptome, indicating a reliable transcriptome. Differential metabolite of root exudates were enriched in amino acid metabolism, glucose metabolism, and fatty acid metabolism pathways. Partial DEGs and differential metabolite are related to photosynthesis. The expression levels of genes related to photosynthesis are decreased in the RE lines. Previous research indicates that 5 to 21% of fixed carbon is transferred to the plant rhizosphere. Our study also identified differences in the composition of root exudates between the RE and WT lines. However, the specific mechanisms underlying the transfer of fixed carbon from photosynthesis to root exudates require further investigation.