NAC transcription factors are key regulators of Brassinolide-Enhanced drought tolerance in Camellia oil tree

Abstract Seasonal drought has hindered the sustainable growth of the Camellia oil tree industry. While brassinolide (BL) can mitigate drought stress in plants to some extent, the regulatory mechanisms underlying BL’s effects in Camellia oil tree remain unclear. To investigate the mechanisms by which BL alleviates drought stress in Camellia oil tree, three-year-old ‘Huashuo’ cutting seedling was exposed to three experimental treatments: CK (normal watering), UW (no watering), and BL (no watering, sprayed with 1 mg∙L− 1 BL). Leaf anatomical observation, hormone quantification, and transcriptomic profiling were performed on leaf samples collected at days 2, 4, and 6 following treatments. The results demonstrated that (i) BL treatment significantly increased leaf and spongy tissue thickness; (ii) BL reduced ABA and IAA levels in leaves under drought stress; (iii) WGCNA identified three modules linked to ABA, IAA, and their corresponding hormone levels, with subsequent analysis infer NAC transcription factors (TFs) as the primary regulators in these modules. This study contributes to a deeper understanding of the role of BL in alleviating drought stress in tree crop and provides a fundamental reference for molecular breeding and genetic improvement of Camellia oil tree.