Putrescine Enhances Seed Germination Tolerance to Heat Stress in Arabidopsis thaliana

Putrescine (Put) as the compound of plant polyamines is catalyzed by arginine decarboxylase (ADC), which is encoded by two members, ADC1 and ADC2 in Arabidopsis, and ADC2 is mainly responsible for Put biosynthesis. Accumulated evidence demonstrates the important function of Put in plant growth and development, but its role in regulating seed germination under high temperature (HT) has not been reported yet. SOMNUS (SOM) is the negative regulator for seed germination thermoinhibition by altering downstream gibberellin (GA) and abscisic acid (ABA) metabolism. In this study, we found exogenous application of Put obviously alleviated the inhibition effect of HT on seed germination. Whereas pharmacological inhibition of endogenous Put level reduced seed germination under HT. Consistently, HT induced the rapid accumulation of Put level, and the adc2 mutant deficiency in Put biosynthesis also showed more sensitivity to HT stress. Furthermore, we found that the Put signal suppressed the expression of SOM and changed the transcriptional patterns of genes associated with GA/ABA metabolism. Genetic analysis also revealed SOM was epistatic to ADC2 to alter GA/ABA metabolism. Collectively, our finding reveals the novel function of Put in controlling seed germination under HT through SOM, and provides the possibility to develop Put as the innovational regulator for uniform seed germination under HT stress.