Spatio-temporal transcriptome reveals the mechanisms of rapeseed in response to low potassium stress and the key role of BnaC6.HAK5 in low potassium resistance

Potassium (K) stress severely constrains plant growth by disrupting ion homeostasis and triggering physiological dysfunction. Investigating the molecular response mechanism of rapeseed under low K (LK) stress is crucial for developing Brassica napus (rapeseed) varieties. In this study, we constructed a time-course study of the transcriptomes in rapeseed under LK stress. Spatiotemporal transcriptomics revealed organ-specific adaptation strategies: roots prioritized sulfur metabolism for defense compound biosynthesis, while leaves modulated iron homeostasis. Weighted co-expression network analysis identified three critical modules, with the M6 module (enriched in phenylpropanoid metabolism and sustained induction) harboring key K transporters. Functional characterization confirmed that BnaC6.HAK5 is a plasma membrane-localized potassium transporter in rapeseed root. Overexpressing BnaC6.HAK5 enhanced K uptake efficiency by 78.7% under LK stress, elevating tissue K content and biomass while reducing osmotic and oxidative stress burdens. Four transcription factors were demonstrated to directly bind the BnaC6.HAK5 promoter, including BnaC7.bHLH147 and BnaA7.MYB3 served as activators, whereas BnaA2.ARF2 and BnaA3.ZRF1b functioned as repressors. Hap2 of BnaC6.HAK5 showed an increased LK tolerance, which can be used as a high-quality haplotype for the subsequent improvement of rapeseed varieties. This study establishes a mechanistic framework that links transcriptional reprogramming, K transporter regulation, and physiological resilience, providing targets for improving rapeseed K efficiency. • A time-course transcriptome profile of rapeseed roots and leaves under low K stress. • Overexpression of BnaC6.HAK5 in rapeseed enhanced the low K resistance. • Overexpression of BnaC6.HAK5 enhanced seed yield at the harvest stage. • Hap2 of BnaC6.HAK5 showed an increased low K tolerance.