Mitochondrial Stress Induces Plant Resistance Through Chromatin Changes

Plants respond more efficiently when confronted with previous similar stress. In the case of pathogens, this memory of a previous infection confers resistance to future ones, which possesses a high potential for agricultural purposes. Some of the defense elements involved in this resistance phenotype, as well as epigenetic mechanisms participating in the maintenance of the memory, are currently known. However, the intracellular cascade from pathogen perception until the establishment of the epigenetic memory is still unexplored. Here, through the induction of mitochondrial stress by exogenous applications of Antimycin A in Arabidopsis thaliana plants, we discovered and characterized a role of mitochondrial stress in plant-induced resistance. Mitochondrial stress-induced resistance (MS-IR) is effective locally, systemically, within generation and transgenerationally. Mechanistically, MS-IR seems to be mediated by priming of defense gene transcription caused by epigenetic changes. On one hand, we observed an increment in the deposition of H3K4me3 (a positive epigenetic mark) at the promoter region of the primed genes, and, on the other hand, the DNA (de)methylation machinery seems to be required for the transmission of MS-IR to the following generations. Finally, we observed that MS-IR is broad spectrum, restricting the colonization by pathogens from different kingdoms and lifestyles. Altogether, this evidence positions mitochondria as a prominent organelle in environment sensing, acting as an integrating platform to process external and internal signals, triggering the appropriate response, and inducing the epigenetic memory of the stress to better react against future stressful conditions.

T-2 Toxin Induces Oxidative Stress at Low Doses via Atf3ΔZip2a/2b-Mediated Ubiquitination and Degradation of Nrf2

T-2 toxin is mainly produced by Fusarium species, which is an extremely toxic mycotoxin to humans and animals. It is well known that T-2 toxin induces oxidative stress, but the molecular mechanism is still unknown. In this study, we found that T-2 toxin significantly promoted reactive oxygen species (ROS) accumulation in MCF-7 cells at low doses which maintains cell viability at least 80%. Further analysis showed that T-2 toxin downregulated the expression of the master regulator of antioxidant defense gene, nuclear factor erythroid 2-related factor (Nrf2), and its targeted antioxidant genes. Overexpression of Nrf2 or its target gene heme oxygenase 1 (HO1) significantly blocked the ROS accumulation in MCF-7 cells under T-2 toxin treatment. Moreover, we found that T-2 toxin downregulated the antioxidant genes via inducing the expression of ATF3ΔZip2a/2b. Importantly, overexpression of ATF3ΔZip2a/2b promoted the ubiquitination and degradation of Nrf2. Altogether, our results demonstrated that T-2 toxin-induced ROS accumulation via ATF3ΔZip2a/2b mediated ubiquitination and degradation of Nrf2, which provided a new insight into the mechanism of T-2 toxin-induced oxidative stress.

Heat Stress Pre-Exposure May Differentially Modulate Plant Defense to Powdery Mildew in a Resistant and Susceptible Barley Genotype

Heat stress negatively affects barley production and under elevated temperatures defense responses to powdery mildew (Blumeria graminis f. sp. hordei, Bgh) are altered. Previous research has analyzed the effects of short-term (30 s to 2 h) heat stress, however, few data are available on the influence of long-term exposure to heat on powdery mildew infections. We simultaneously assessed the effects of short and long term heat pre-exposure on resistance/susceptibility of barley to Bgh, evaluating powdery mildew infection by analyzing symptoms and Bgh biomass with RT-qPCR in barley plants pre-exposed to high temperatures (28 and 35 °C from 30 s to 5 days). Plant defense gene expression after heat stress pre-exposure and inoculation was also monitored. Our results show that prolonged heat stress (24, 48 and 120 h) further enhanced Bgh susceptibility in a susceptible barley line (MvHV118-17), while a resistant line (MvHV07-17) retained its pathogen resistance. Furthermore, prolonged heat stress significantly repressed the expression of several defense-related genes (BAX inhibitor-1, Pathogenesis related-1b and Respiratory burst oxidase homologue F2) in both resistant and susceptible barley lines. Remarkably, heat-suppressed defense gene expression returned to normal levels only in MvHV07-17, a possible reason why this barley line retains Bgh resistance even at high temperatures.

T-2 Toxin Induces Oxidative Stress at Low Doses Via ATF3∆Zip2a/2b-Mediated Ubiquitination and Degradation of Nrf2

Background: T-2 toxin is mainly produced by Fusarium species, which is an extremely toxic mycotoxin to humans and animals. It is well known that T-2 toxin induces oxidative stress, but the molecular mechanism is still unknown. Results: In this study, we found that T-2 toxin significantly promoted ROS accumulation in MCF-7 cells at low doses which maintains cell viability at least 80%. Further analysis showed that T-2 toxin downregulated the expression of the master regulator of antioxidant defense gene, Nrf2, and its targeted antioxidant genes. Overexpression of Nrf2 or its target gene HO1 significantly blocked the ROS accumulation in MCF-7 cells under T-2 toxin treatment. Moreover, we found that T-2 toxin downregulated the antioxidant genes via inducing the expression of ATF3∆Zip2a/2b. Importantly, overexpression of ATF3∆Zip2a/2b promoted the ubiquitination and degradation of Nrf2. Conclusions: This work demonstrated that T-2 toxin induced ROS accumulation via ATF3∆Zip2a/2b mediated ubiquitination and degradation of Nrf2, which provided a new insight into the mechanism of T-2 toxin-induced oxidative stress.

A small cysteine-rich phytotoxic protein of Phytophthora capsici functions as both plant defense elicitor and virulence factor

Small cysteine-rich (SCR) proteins including fungal avirulence proteins play important roles in the pathogen-plant interactions. SCR protein-encoding genes have been discovered in the genomes of Phytophthora pathogens, but their functions during the pathogenesis remain obscure. Here, we report the characterization of one Phytophthora capsici SCR protein, namely SCR82 with similarity to Phytophthora cactorum phytotoxic protein PcF. The scr82 gene has 10 allelic sequences in the P. capsici population. Homologues of SCR82 were not identified in fungi or other organisms but in Phytophthora relative species. Initially scr82 was weakly expressed during the mycelium, sporangium and zoospore stages, but quickly upregulated when the infection initiated. Both ectopic expression of SCR82 and recombinant yeast-expressed protein (rSCR82) caused cell death on tomato leaves. Upon treatment, rSCR82 induced plant defense responses including the induction of defense gene expression, reactive oxygen species burst and callose deposition. Knockout of scr82 in P. capsici by CRISPR/Cas9 severely impaired its virulence on host plants and reduced significantly its resistance againstoxidative stress. Inversely, its overexpression increased the pathogen’s virulence and tolerance to oxidative stress. Our results collectively demonstrate that SCR82 functions as both an important virulence factor and plant defense elicitor, which is conserved across Phytophthora species.

The secreted peptide IRP functions as a DAMP in rice immunity

ABSTRACTSmall signaling peptides play important roles in various plant processes, but information regarding their involvement in plant immunity is limited. We previously identified a novel small secreted protein in rice, named immune response peptide (IRP) by the integrated multi-omics analyses. Here, we studied IRP functions in rice immunity. Rice plants overexpressing IRP enhanced resistance to the blast fungus. Application of the IRP peptide to rice suspension cells triggered the expression of IRP itself and defense gene PAL1. RNA-seq results revealed that 84% of genes upregulated by IRP peptide were also induced by chitin, including 13 OsWRKY transcription factors, indicating that IRP and chitin share the similar signaling pathway. Co-treatment with chitin and IRP elevated the expression level of PAL1 and OsWRKYs in an additive manner. When results of IRP and PAL1 expression and MAPK activation by IRP were compared with those by chitin, IRP had a stronger effect on MAPK activation rather than IRP and PAL1 expression. Collectively, our findings indicate that IRP functions as a damage-associated molecular pattern (DAMP) in rice immunity, regulating MAPKs and OsWRKYs to amplify chitin signaling, and provide new insights into how PAMPs and DAMPs cooperatively regulate rice immunity.

Maize Plants Chimeric for an Autoactive Resistance Gene Display a Cell Autonomous Hypersensitive Response but Non-Cell Autonomous Defense Signaling.

The maize gene Rp1-D21 is a mutant form of the gene Rp1-D that confers resistance to common rust. Rp1-D21 triggers a spontaneous defense response that occurs in the absence of the pathogen and includes a programed cell death called the hypersensitive response (HR). Eleven plants heterozygous for Rp1-D21, in four different genetic backgrounds, were identified that had chimeric leaves with lesioned sectors showing HR abutting green non-lesioned sectors lacking HR. The Rp1-D21 sequence derived from each of the lesioned portions of leaves was unaltered from the expected sequence whereas the Rp1-D21 sequences from nine of the non-lesioned sectors displayed various mutations and we were unable to amplify Rp1-D21 from the other two non-lesioned sectors. In every case, the borders between the sectors were sharp with no transition zone, suggesting that HR and chlorosis associated with Rp1-D21 activity was cell-autonomous. Expression of defense response marker genes was assessed in the lesioned and non-lesioned sectors as well as in near-isogenic plants lacking and carrying Rp1-D21. Defense gene expression was somewhat elevated in non-lesioned sectors abutting sectors carrying Rp1-D21 compared to near-isogenic plants lacking Rp1-D21. This suggests that while the HR itself was cell autonomous, other aspects of the defense response initiated by Rp1-D21 were not.