DNA Damage and Chromatin Conformation Changes Confer Nonhost Resistance: A Hypothesis Based on Effects of Anti-cancer Agents on Plant Defense Responses

Abstract

Over the last decades, medical research has utilized DNA altering procedures in cancer treatments with the objective of killing cells or suppressing cell proliferation. Simultaneous research related to enhancing disease resistance in plants reported that alterations in DNA can enhance defense responses. These two opposite perspectives have in common their effects on the center for gene transcription, the nuclear chromatin. A review of selected research from both anticancer- and plant defense-related research provides examples of some specific DNA altering actions: DNA helical distortion, DNA intercalation, DNA base substitution, DNA single cleavage by DNases, DNA alkylation/methylation, and DNA binding/exclusion. The actions of the pertinent agents are compared, and their proposed modes of action are described in this study. Many of the DNA specific agents affecting resistance responses in plants, e.g., the model system using pea endocarp tissue, are indeed anticancer agents. The tumor cell death or growth suppression in cancer cells following high level treatments may be accompanied with chromatin distortions. Likewise, in plants, DNA-specific agents activate enhanced expression of many genes including defense genes, probably due to the chromatin alterations resulting from the agents. Here, we propose a hypothesis that DNA damage and chromatin structural changes are central mechanisms in initiating defense gene transcription during the nonhost resistance response in plants.

Nonhost Disease Resistance in Pea: Chitosan’s Suggested Role in DNA Minor Groove Actions Relative to Phytoalexin-Eliciting Anti-Cancer Compounds

“…Poly-L-lysine molecules and many other cationic molecules are efficient elicitors of defense responses in pea endocarp tissue, some of which are compounds that can reside in the DNA minor groove [ 6 ]. This proposed action directly on plant chromatin helps confirm that a mechanism by-passing recognition at the plant membrane may initiate a major route towards defense gene regulation.…”

“…Smaller compounds called phytoalexins (e.g., pisatin) ( Figure 2) [33] are newly synthesized in plants following pathogen challenge. The pisatin pathway is activated by an array of DNA-specific agents [6,8] and by many non-pathogenic organisms. Virulent organisms contacting plant tissue trigger some of the same responses as the avirulent pathogens [3].…”

“…Features of the induced chromatin alterations include the binding of the positive elicitor charge with the negative charges of DNA, recognition of DNA sequences, and the hypothesized expansion of the minor groove occurring in the bound DNA. These changes are likely part of the more dramatic actions of other pisatin inducers that cleave DNA strands or intercalate between DNA base pairs [ 4 , 6 ] that can activate the “nonhost resistance” defense response of plants [ 5 , 7 ]. The current case study is an assimilation of long-term research relating how fungal signals develop nonhost resistance in pea tissue, monitored here as pisatin production.…”

“…Alterations of DNA [ 7 ], including intercalation of base pair substitutions, DNA repair, DNA cleavage [ 6 ], and DNA crosslinking [ 34 ], can influence transcription [ 35 ]. The mechanism of cellular action is known for a number of the chemical compounds that were investigated and identified in searches for DNA compounds that kill cancer cells.…”

In SilicoPhylogenetic and Structural Analyses of Plant Endogenous Danger Signaling Molecules upon Stress

“…It has been reported that sDNA can trigger ROS- and MAPK-dependent signaling cascades [20], alter the CpG DNA methylation status (hypomethylation), and elicit defense-related responses [21]. Moreover, DNA damage and alteration of the primary chromatin structure were shown to induce the expression of defense-related genes [22, 23]. Elucidation of the plant-specific receptors that recognize extracellular sDNA as DAMPs could advance our knowledge on sDNA-dependent danger signaling in plant cells.…”