Auxin accumulation mediated by the CsPIF1-like-CsYUC8 module drives high temperature-induced hypocotyl elongation in cucumber

• High temperature promotes hypocotyl elongation in cucumber seedlings. • Elevated auxin levels under high temperature are a key driver of hypocotyl elongation. • High temperature induces the transcription of the auxin biosynthesis gene CsYUC8 . • CsPIF1-like positively regulates CsYUC8 expression under high temperature. High temperature trigger various thermomorphogenic adaptations in plants, such as hypocotyl elongation, which disrupts developmental homeostasis and threaten agricultural productivity. However, the molecular mechanism underlying hypocotyl elongation in cucumber under high-temperature conditions remain poorly characterized. Here, we revealed that the increased auxin biosynthesis is a pivotal driver of high-temperature-induced hypocotyl elongation in cucumber. Transcript profiling indicated that CsYUC8 , a gene encoding a key auxin biosynthetic enzyme, was upregulated in cucumber hypocotyl elongation under high-temperature conditions. Functional analysis and NPA (auxin inhibitor) treatments demonstrated that CsYUC8- mediated auxin accumulation is essential for thermomorphogenic hypocotyl elongation. Furthermore, we identified a heat-responsive bHLH transcription factor, CsPIF1-like , which directly binds to the CsYUC8 promoter to activate its expression. Those results revealed a CsPIF1-like- CsYUC8 regulatory module that fine-tunes auxin-dependent hypocotyl elongation in cucumber, providing a mechanistic framework for improving heat resilience in cucurbit crops.