RGF signaling bridges root development and nonlethal thermal stress adaptation.

Roots adapt to growth-restricting but nonlethal high temperatures. Although lethal heat shock and moderately elevated temperatures have been extensively studied, the effects of nonlethal thermal stress on root development remain unclear. We defined 31°C as a nonlethal thermal stress condition in Arabidopsis thaliana and examined its effects using phenotypic and transcriptomic analyses. Compared with 22°C, growth at 31°C reduced primary root growth, meristem size, and superoxide (O2˙-) accumulation, accompanied by altered redox states, restricted distribution of the meristem regulator PLETHORA2 (PLT2), and accelerated differentiation. Transcriptome analyses showed repression of meristem-associated genes and induction of differentiation-related genes rather than activation of canonical heat-shock genes. Mutants defective in the RGF-RGFR-PLT2 pathway were hypersensitive to nonlethal thermal stress. By contrast, exogenous RGF treatment restored primary root meristem defects and promoted lateral root elongation under prolonged stress. These findings indicate that the RGF-RGFR-PLT2 pathway plays a central role in root adaptation to nonlethal thermal stress and suggest that manipulation of RGF signaling could improve root thermotolerance and crop resilience under elevated temperatures.