Comparative Transcriptomic Analysis of <scp>AtBBX29</scp> Transgenic and Wild Type Sugarcane Exposed to Drought Stress

Previously, we produced drought-tolerant transgenic sugarcane plants that overexpressed the AtBBX29 gene, which encodes a transcription factor (TF) B-box protein. These plants displayed delayed senescence, were able to maintain photosynthesis, and accumulated high levels of antioxidants and osmolytes when exposed to water deficit stress compared with wild type (WT) plants. To unravel the molecular mechanisms underlying the enhanced drought tolerance in these plants, in the current study, we compared the transcriptomes of the AtBBX29 transgenic and WT plants exposed to water deficit stress using RNA sequencing. Using comparative transcriptome analysis, we identified up to 4039 differentially expressed genes (DEGs) in the stressed WT and transgenic plants compared to their non-stressed controls. A further 131 DEGs were identified when comparing the stressed WT with the stressed transgenic plants. Notably, under stress, DEGs were linked to complex stress perception and signaling, various TFs, photosynthesis and nitrogen metabolism, senescence, and oxidative stress detoxification. In the transgenic plants, TFs likely linked to the abscisic acid (ABA)-independent stress response pathway (HSF, DREB, GTE7, and AP2/ERF) and glutathione regulation were upregulated, while transcripts in the KEGG pathways linked to the photosystem I (PSI) were downregulated compared to the non-stressed plants. In the WT plants, some TFs linked to the ABA-dependent stress response pathway were downregulated (HTH-MYB domain and BBX24), while transcripts linked to senescence were uniquely upregulated in the stressed WT plants, and KEGG pathways mapping amino acid metabolism were upregulated. The differentially expressed profiles between WT and AtBBX29 overexpressing sugarcane established by this study provide important insights into the molecular mechanisms behind the AtBBX29-mediated drought-tolerant phenotype of the transgenic plants.