ABA Enhances Drought Resistance During Rapeseed (Brassica napus L.) Seed Germination Through the Gene Regulatory Network Mediated by ABA Insensitive 5

ABA Insensitive 5 (ABI5) is a basic leucine zipper (bZIP) transcription factor (TF) that plays a critical role in seed dormancy and germination, particularly under stress conditions. This study identified <i>ABI5</i> as an important candidate gene regulating seed germination under drought stress during early germination in rapeseed (<i>Brassica napus</i> L.) seeds through Genome-Wide Association Study (GWAS). Using Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 (CRISPR/CAS9) technology, <i>ABI5</i> mutant plants were generated, showing higher germination rates and more developed root systems at 72 h. Transcriptomic analysis of wild-type (WT) and mutant seeds under water, 2μM of abscisic acid (ABA), and 10% PEG treatments after 0, 24, 48, and 72 h revealed complex changes in gene regulatory networks due to <i>ABI5</i> mutation. Differential expression analysis showed that the number of downregulated differentially expressed genes (DEGs) in the mutant was significantly higher than upregulated DEGs at multiple time points and treatments, indicating a negative regulatory role for <i>ABI5</i> in gene expression. Weighted Gene Co-Expression Network Analysis (WGCNA) revealed that genes related to ABA content, such as those in the glutathione metabolism pathway, were similarly downregulated in the <i>ABI5</i> mutants. Key genes, including <i>BnA03g0120550.1</i> (<i>GST</i>), <i>BnA09g0366300.1</i> (<i>GST</i>), <i>BnA10g0413960.1</i> (<i>gshA</i>), and <i>BnC02g0518750.1</i> (<i>GST</i>), were identified as potential candidates in <i>ABI5</i>-regulated drought responses. Additionally, TFs involved in regulating the glutathione metabolism pathway were identified, providing insights into the collaboration of <i>ABI5</i> with other TF. This comprehensive transcriptomic analysis of <i>ABI5</i> mutant plants highlights how <i>ABI5</i> affects gene expression in multiple pathways, impacting seed germination and drought resistance, offering a foundation for improving drought tolerance in rapeseed.