Thermosensory reconfiguration of the auxin transcriptional pathway to drive root cell growth

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. While auxin typically inhibits root cell growth, elevated temperatures reconfigure the auxin transcriptional pathway to promote elongation. This study reveals how plants reprogram core hormonal signalling to adjust their internal biology to rising temperatures.