Extracellular Fragmented Self-DNA Is Involved in Plant Responses to Biotic Stress

Abstract

A growing body of evidence indicates that extracellular fragmented self-DNA (eDNA), by acting as a signaling molecule, triggers inhibitory effects on conspecific plants and functions as a damage-associated molecular pattern (DAMP). To evaluate early and late events in DAMP-dependent responses to eDNA, we extracted, fragmented, and applied the tomato (Solanum lycopersicum) eDNA to tomato leaves. Non-sonicated, intact self-DNA (intact DNA) was used as control. Early event analyses included the evaluation of plasma transmembrane potentials (Vm), cytosolic calcium variations (Ca2+cyt), the activity and subcellular localization of both voltage-gated and ligand-gated rectified K+ channels, and the reactive oxygen species (ROS) subcellular localization and quantification. Late events included RNA-Seq transcriptomic analysis and qPCR validation of gene expression of tomato leaves exposed to tomato eDNA. Application of eDNA induced a concentration-dependent Vm depolarization which was correlated to an increase in (Ca2+)cyt; this event was associated to the opening of K+ channels, with particular action on ligand-gated rectified K+ channels. Both eDNA-dependent (Ca2+)cyt and K+ increases were correlated to ROS production. In contrast, application of intact DNA produced no effects. The plant response to eDNA was the modulation of the expression of genes involved in plant–biotic interactions including pathogenesis-related proteins (PRPs), calcium-dependent protein kinases (CPK1), heat shock transcription factors (Hsf), heat shock proteins (Hsp), receptor-like kinases (RLKs), and ethylene-responsive factors (ERFs). Several genes involved in calcium signaling, ROS scavenging and ion homeostasis were also modulated by application of eDNA. Shared elements among the transcriptional response to eDNA and to biotic stress indicate that eDNA might be a common DAMP that triggers plant responses to pathogens and herbivores, particularly to those that intensive plant cell disruption or cell death. Our results suggest the intriguing hypothesis that some of the plant reactions to pathogens and herbivores might be due to DNA degradation, especially when associated to the plant cell disruption. Fragmented DNA would then become an important and powerful elicitor able to trigger early and late responses to biotic stress.

Extracellular DNA: Insight of a Signal Molecule in Crop Protection

“…Contrastingly, an up-regulation of MPK3 and OXI1 genes resulted from treatments with broccoli, citrus, bean, and maize eDNA. Similarly, CML37 levels of expression were upregulated in A. thaliana plants treated with broccoli and bean eDNA only [60]. In this case, the non-self eDNA had neither pathogenic nor microbial origin to support the hypothesis of the eDNA effect as MAMP/PAMP but these results do support the phylogenetically closeness-related effect described earlier [46,52].…”

“…As reported before [47,60], the plant immune system responds to the detection of both self and non-self eDNA. Due to the effect on plant metabolism seems to be different between eDNA sources, these results suggest a role of eDNA different from the suspected DAMP or MAMP (PAMP) role as a biological plant biostimulant (considering a hormetic effect), activating several metabolic pathways related to both defence and growth processes depending on the dose and the opportunity of applications during plant phenology.…”

“…New studies have focused on understanding the effect of self eDNA in plants in a more global way. Barbero et al [60] identified as an effect of self eDNA treatment in tomato plants a negative regulation of genes related to gene ontology terms such as metabolic and biosynthetic processes of Myo-inositol (>100-fold enrichment), nitric oxide metabolic and biosynthetic processes (>70-fold enrichment), biosynthetic processes of ROS, cell wall, jasmonic acid, and sucrose transport (>47 fold enrichment). Additionally, several genes were identified as upregulated and related to the following gene ontology terms: oxygen transport, defence against Gram-negative bacteria, and lactate biosynthetic processes (>66-fold enrichment), adenine biosynthetic, and metabolic processes, auxin influx, and cellular ion homeostasis processes (>33-fold enrichment).…”

Effects of Extracellular Self- and Nonself-DNA on the Freshwater Microalga Chlamydomonas reinhardtii and on the Marine Microalga Nannochloropsis gaditana

“…Moreover, fragmented self-exDNA induces intracellular calcium signalling and plasma membrane depolarization [ 87 ], H 2 O 2 production, and MAPK activation [ 55 ] in plants. Recently, it has been shown that after treatment with self-exDNA, tomato leaves activate a typical response to biotic stress characterized by an early response consisting of the plasma membrane depolarization, the increase of intracellular concentration of Ca 2+ and K + ions, and ROS production, accompanied by the modulation of genes involved in plant late responses to biotic stress [ 88 ].…”

Crosstalk between Ca2+ and Other Regulators Assists Plants in Responding to Abiotic Stress

“…In contrast, high-temperature stress also activates mitogen-activated protein kinases (MAPKs) and regulates the expression of HSP genes. This may be closely related not only to changes in membrane fluidity but also to calcium signaling induced by high-temperature stress, which is especially required for HSP gene expression and high-temperature stress tolerance acquisition [ 79 , 80 ]. The common features between signals of low- and high-temperature stress are not limited to membrane fluidity changes, calcium signaling and MAPK activation, as they also include ROS, NO, and phospholipid signaling [ 81 , 82 ].…”