Abstract
Elevated temperatures enhance plant root growth. We find that cell elongation significantly contributes to this response. While mutations in the auxin transcriptional pathway impair warmth-induced cell elongation, exogenous auxin inhibits this growth. Intriguingly, warmth increases auxin levels and the nuclear accumulation of TIR1/AFB2/AFB3, alongside Aux/IAA stabilisation. This apparent paradox is explained by the concurrent increase in nuclear AFB1, which stabilises Aux/IAAs and promotes cell elongation. Notably, despite enhancing Aux/IAA stability, warmth also promotes ARF transcriptional activity. ARF7/19 are essential for warmth-induced cell growth and its inhibition by exogenous auxin. Warmth directly modulates ARF7/19 by reducing oligomerisation and cytoplasmic condensation, thereby enhancing their nuclear accumulation. This mechanism effectively repurposes the auxin pathway to regulate root cell growth in response to temperature.