Effects of Harpin and Flg22 on Growth Enhancement and Pathogen Defense in Cannabis sativa Seedlings

Pathogen-associated molecular patterns, PAMPs, are a diverse group of molecules associated with pathogenic microbes and are known to activate immune response and in some cases enhance growth in plants. Two PAMPs, harpin and flg22, have shown these affects in various plant species. PAMPs are known to activate basal immunity, the ethylene signaling pathway, alter gene expression and change plant composition. Pretreatment with harpin enhanced hemp seedling resistance to Pythium aphanidermatum, while flg22 failed to induce the defense mechanism towards P. aphanidermatum. In the absence of the pathogen, both harpin and flg22 enhanced seedling growth when compared to the water control. Ethylene is a hormone involved in both plant defense signaling and growth. Both harpin and flg22 pretreatment induced certain ethylene responsive genes but not all the genes examined, indicating that harpin and flg22 act differently in ethylene and potentially defense signaling. In addition, both harpin and flg22 induced CsFRK1 and CsPR1, two marker genes for plant innate immunity. Both PAMPs can enhance growth but likely induce different defense signaling pathways.