Salt stress-induced polyamine biosynthesis contributes to blast resistance in rice

Abstract Rice blast, caused by the fungal pathogen Magnaporthe oryzae , is a destructive disease that affects rice ( Oryzae sativa L.) on a global scale. Polyamines (PAs) play diverse roles in plant growth and development and responses to biotic and abiotic stimuli. Putrescine (PUT), spermidine (SPD), and spermine (SPM) are the primary forms of polyamines (PAs). In this study, we observed that the accumulation of apoplastic PAs significantly increased in rice plants after treatment with salt or M. oryzae . The salt-treated plants exhibited enhanced resistance to rice blast disease. RNA sequencing data indicate that S-adenosylmethionine decarboxylase (SAMDC), a key enzyme involved in the synthesis of polyamines, plays a significant role in enhancing plant resistance. Overexpression of rice SAMDC ( OsSAMDC ) led to a significant decrease of pathogen infection in the transgenic rice plants. Additionally, OsSAMDC overexpression plants accumulated polyamines in the cytosol and apoplast, particularly SPD and SPM. Conversely, the disease resistance and accumulation of PAs were reduced in OsSAMDC- silenced plants. Exogenous application of PAs inhibited the mycelium growth, spore germination, germ tube elongation, and appressorium formation in M. oryzae . These results demonstrated that OsSAMDC -mediated polyamine biosynthesis, especially SPD and SPM, plays an essential role in rice plants to resist biotic and abiotic stresses.