Unlocking the Synergy: ABA Seed Priming Enhances Drought Tolerance in Seedlings of Sweet Sorghum Through ABA-IAA...

Abscisic acid (ABA) seed priming impacts plant growth and stress resistance, yet its precise physiological and molecular mechanisms remain elusive. This study explored the role of ABA-priming in enhancing drought acclimation in sweet sorghum (Sorghum bicolor Moench) using physiological assessments and comparative transcriptomics. Under drought stress, ABA-primed seedlings exhibited increased plant height, larger leaves, and higher leaf water content compared to non-primed plants. While drought negatively affected photosynthesis through the regulation of photosystem I and II, ABA-priming improved photosynthesis and WUE by involving in differential expression of photosystem II genes. ABA-priming promoted the accumulation of cuticular wax and cutin, effectively reducing leaf water loss. Drought triggered endogenous ABA production via ABA inactivation genes (UGT, BGLU), while ABA-priming activated auxin (IAA) biosynthesis via YUCCA, enhancing auxin-mediated responses and gibberellic acid (GA) signalling. The synergistic action of ABA and IAA culminated in enhanced drought tolerance. Additionally, ABA-priming and drought stress regulated NAC transcription factors, with SbNAC21-1 emerging as a pivotal transcriptional activator intricately linked to auxin signalling. Overexpression of SbNAC21-1 in Arabidopsis effectively enhanced drought tolerance. These findings offer valuable insights into the intricate mechanisms underpinning the beneficial effects of ABA-priming, ultimately enhancing plant adaptability to environmental stressors.