Spermine inhibits pathogen-associated molecular pattern (PAMP) ROS and Ca²⁺ burst and reshapes the transcriptional landscape of PAMP-triggered immunity in Arabidopsis thaliana

Abstract

Polyamines are small polycationic amines which levels increase during defense. Previous studies support the contribution of the polyamine spermine (Spm) to the establishment of the hypersensitive response (HR) during incompatible plant-pathogen interactions. However, the potential contribution of Spm to other layers of defense, and pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) in particular, was not completely established. Here we compared the contribution of Spm and putrescine (Put) to early and late PTI responses. We find that Put and Spm show opposite effects on PAMP-elicited reactive oxygen species (ROS) production, with Put increasing whereas Spm lowering flg22-stimulated ROS burst. Through genetic and pharmacological approaches, we find that the inhibitory effect of Spm on flg22-elicited ROS is independent of polyamine oxidation and EDS1 (ENHANCED DISEASE SUSCEPTIBILITY 1), PAD4 (PHYTOALEXIN DEFICIENT 4), salicylic acid and NPR1 (NONEXPRESSER OF PR GENES 1) defense components but resembles chemical inhibition of RBOHD (RESPIRATORY BURST OXIDASE HOMOLOG D) function. Remarkably, Spm can also suppress ROS elicited by FLS2-independent but RBOHD-dependent pathways, thus pointing to compromised RBOHD function. Consistent with this, we find that Spm dampens flg22-stimulated cytosolic Ca2+ influx necessary for RBOHD function and reshapes the transcriptional landscape of PTI and defense responses against Pseudomonas syringae pv. tomato DC3000. Overall, we provide molecular evidence for the differential contribution of Put and Spm to PTI with an impact on plant defense.