Root meristem growth factor (RGF) peptide signaling as a molecular bridge between root development and non-lethal thermal stress adaptation

O_LIRoots adapt to temperature ranges that restrict growth but are not lethal. Although lethal heat shock and moderately high temperatures have been studied in detail, the effects of non-lethal high temperatures on root development remain largely unknown. We defined 31{degrees}C as a non-lethal thermal stress in Arabidopsis thaliana and examined its impact on root growth using phenotypic analyses and developmental-zone-specific transcriptomics. C_LIO_LICompared to growth at 22{degrees}C, at 31{degrees}C, primary root growth, meristem size, and superoxide (O2-) accumulation were reduced, and the distribution of the meristem master regulator PLETHORA2 (PLT2) became restricted. Transcriptome analysis revealed a strong downregulation of RGFs, RGFRs, and PLT2, rather than activation of heat shock-inducible genes. C_LIO_LIThese gene mutants were more sensitive to non-lethal thermal stress. In contrast, RGF treatment recovered heat-stress-induced defects. Beyond alleviating the stress in the primary root meristem, RGF treatments promoted lateral root elongation under prolonged non-lethal thermal stress, resulting in a more complex root system. C_LIO_LIThese results indicate that the RGF-RGF receptor-PLT2 pathway plays a central role in root adaptation to non-lethal heat stress rather than the canonical heat shock response pathway and suggest that manipulating RGF signaling could enhance root thermotolerance and crop resilience under elevated temperatures. C_LI