Alcazar, R. | Search bioRxiv

bioRxiv2022

Spermine inhibits PAMP- elicited ROS and Ca2+ burst and reshapes the transcriptional landscape of PTI in Arabidopsis

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.

plant biology↗

bioRxiv2021

The receptor kinase SRF3 coordinates iron-level and flagellin dependent defense and growth responses in plants

Iron is critical for host-pathogen interactions. While pathogens seek to scavenge iron to spread, the host aims at decreasing iron availability to reduce pathogen virulence. Thus, iron sensing and homeostasis are of particular importance to prevent host infection and part of nutritional immunity. While the link between iron homeostasis and immunity pathways is well established in plants, how iron levels are sensed and integrated with immune response pathways remain unknown. We identified a receptor kinase, SRF3 coordinating root growth, iron homeostasis and immunity pathways via regulation of callose synthase activity. These processes are modulated by iron levels and rely on SRF3 extracellular and kinase domain which tune its accumulation and partitioning at the cell surface. Mimicking bacterial elicitation with the flagellin peptide flg22 phenocopies SRF3 regulation upon low iron levels and subsequent SRF3-dependent responses. We propose that SRF3 is part of nutritional immunity responses involved in sensing external iron levels.

plant biology↗