HB52-PUT2 Module-Mediated Polyamine Shoot-to-Root Movement Regulates Salt Stress Tolerance in Tomato

Soil salinity severely restricts crop quality and yields. Plants have developed various strategies to alleviate salinity stress's negative effects, including polyamine redistribution by polyamine uptake transporters (PUTs). However, the mechanisms by which PUTs alter polyamine translocation processes during salt stress have not been fully elucidated. Here, we show that disruption of PUT2, which is involved in polyamine shoot-to-root transport, results in salt sensitivity phenotypes in tomato. Moreover, yeast one-hybrid screened for an HD-Zip transcription factor HB52 that interacts with PUT2, and loss of function of HB52 also led to increased sensitivity to salt stress, whereas HB52-overexpression lines exhibited improved salt tolerance. Furthermore, molecular analyses demonstrated that HB52 directly activated the expression of PUT2 and facilitated Na⁺ efflux by promoting polyamine shoot-to-root mobility. This study uncovers a synergistic transcriptional regulatory network associated with a homeobox protein regulator that promotes polyamine long-distance transport under salt stress.