Dissecting Contrasts in Cell Death, Hormone, and Defense Signaling in Response to Botrytis cinerea and Reactive Oxygen Species

Plant immune inducer ZNC promotes rutin accumulation and enhances resistance to Botrytis cinerea in tomato

Gray mold is a destructive disease caused by Botrytis cinerea, a pervasive plant pathogen, which poses a threat to both tomato growth and postharvest storage. The utilization of induced resistance presents a potential strategy for combating plant pathogenic attacks. ZNC (zhinengcong), an extract derived from the endophytic fungus Paecilomyces variotii, has been discovered to play a vital role in preventing diverse forms of bacterial infections. Nevertheless, the precise mechanism behind its ability to enhance tomato resistance to fungi remains unclear. In this study, we found that the exogenous spraying of ZNC could significantly improve the resistance of tomato plants to B. cinerea. The results of both the metabolomic analysis and high-performance liquid chromatography (HPLC) demonstrated that tomato plants responded to ZNC treatment by accumulating high levels of rutin. Additional transcriptome analysis uncovered that rutin enhances tomato resistance possible by initiating the generation of reactive oxygen species (ROS) and phosphorylation of mitogen-activated protein kinases (MPKs) related genes expression during the initial phase of invasion by B. cinerea. In addition, we also found that rutin might activate plant immunity by eliciting ethylene (ET) and jasmonic acid (JA)-mediated pathways. Therefore, plant immune inducer ZNC and rutin has bright application prospects and high utilization value to control gray mold.

Ozone-Induced Biochemical and Molecular Changes in Vitis vinifera Leaves and Responses to Botrytis cinerea Infections

To investigate how plants cope with multi-stress conditions, we analyzed the biochemical and molecular changes of Vitis vinifera leaves subjected to single or sequential double stresses (infection by Botrytis cinerea (Bc) and ozone (O₃, 100 ppb for 3 h) treatment). In Bc⁺/O₃^- leaves, the hydrogen peroxide (H₂O₂) induction (observed at 12 and 24 h from the end of treatment (FET)) triggered a production of ethylene (Et; +35% compared with Bc^-/O₃^- leaves), which was preceded by an increase of salicylic acid (SA; +45%). This result confirms a crosstalk between SA- and Et-related signaling pathways in lesion spread. The ozone induced an early synthesis of Et followed by jasmonic acid (JA) and SA production (about 2-fold higher), where Et and SA signaling triggered reactive oxygen species production by establishing a feedback loop, and JA attenuated this cycle by reducing Et biosynthesis. In Bc⁺ + O₃⁺ leaves, Et peaked at 6 and 12 h FET, before SA confirmed a crosstalk between Et- and SA-related signaling pathways in lesion propagation. In O₃⁺ + Bc⁺ leaves, the H₂O₂ induction triggered an accumulation of JA and Et, demonstrating a synergistic action in the regulation of defence reactions. The divergence in these profiles suggests a rather complex network of events in the transcriptional regulation of genes involved in the systemic acquired resistance.

The immunity priming effect of the Arabidopsis phyllosphere resident yeast Protomyces arabidopsidicola strain C29

The phyllosphere is a complex habitat for diverse microbial communities. Under natural conditions, multiple interactions occur between host plants and phyllosphere resident microbes, such as bacteria, oomycetes, and fungi. Our understanding of plant associated yeasts and yeast-like fungi lags behind other classes of plant-associated microbes, largely due to a lack of yeasts associated with the model plant Arabidopsis, which could be used in experimental model systems. The yeast-like fungal species Protomyces arabidopsidicola was previously isolated from the phyllosphere of healthy wild-growing Arabidopsis, identified, and characterized. Here we explore the interaction of P. arabidopsidicola with Arabidopsis and found P. arabidopsidicola strain C29 was not pathogenic on Arabidopsis, but was able to survive in its phyllosphere environment both in controlled environment chambers in the lab and under natural field conditions. Most importantly, P. arabidopsidicola exhibited an immune priming effect on Arabidopsis, which showed enhanced disease resistance when subsequently infected with the fungal pathogen Botrytis cinerea. Activation of the mitogen-activated protein kinases (MAPK), camalexin, salicylic acid, and jasmonic acid signaling pathways, but not the auxin-signaling pathway, was associated with this priming effect, as evidenced by MAPK3/MAPK6 activation and defense marker expression. These findings demonstrate Arabidopsis immune defense priming by the naturally occurring phyllosphere resident yeast species, P. arabidopsidicola, and contribute to establishing a new interaction system for probing the genetics of Arabidopsis immunity induced by resident yeast-like fungi.

The coordination of melatonin and anti-bacterial activity by EIL5 underlies ethylene-induced disease resistance in cassava

Ethylene and melatonin are widely involved in plant development and environmental stress responses. However, the role of their direct relationship in the immune response and the underlying molecular mechanisms in plants remain elusive. Here, we found that Xanthomonas axonopodis pv. manihotis (Xam) infection increased endogenous ethylene levels, which positively modulated plant disease resistance through activating melatonin accumulation in cassava. In addition, the ethylene-responsive transcription factor ETHYLENE INSENSITIVE LIKE5 (MeEIL5), a positive regulator of disease resistance, was essential for ethylene-induced melatonin accumulation and disease resistance in cassava. Notably, the identification of heat stress transcription factor 20 (MeHsf20) as an interacting protein of MeEIL5 indicated the association between ethylene and melatonin in plant disease resistance. MeEIL5 physically interacted with MeHsf20 to promote the transcriptional activation of the gene encoding N-acetylserotonin O-methyltransferase 2 (MeASMT2), thereby improving melatonin accumulation. Moreover, MeEIL5 promoted the physical interaction of MeHsf20 and pathogen-related gene 3 (MePR3), resulting in improved anti-bacterial activity of MePR3. This study illustrates the dual roles of MeEIL5 in fine-tuning MeHsf20-mediated coordination of melatonin biosynthesis and anti-bacterial activity, highlighting the ethylene-responsive MeEIL5 as the integrator of ethylene and melatonin signals in the immune response in cassava.

IQD1 Involvement in Hormonal Signaling and General Defense Responses Against Botrytis cinerea

IQ Domain 1 (IQD1) is a novel Arabidopsis thaliana calmodulin-binding protein, which was found to be a positive regulator of glucosinolate (GS) accumulation and plant defense responses against insects. We demonstrate here that the IQD1 overexpressing line (IQD1 ^OXP ) was also more resistant also to the necrotrophic fungus Botrytis cinerea, whereas an IQD1 knockout line (iqd1-1) was much more sensitive. Furthermore, we showed that IQD1 is up-regulated by jasmonic acid (JA) and downregulated by salicylic acid (SA). A comparison of whole transcriptome expression between iqd1-1 and wild type plants revealed a substantial downregulation of genes involved in plant defense and hormone regulation. Further examination revealed a marked reduction of SA and increases in the levels of ethylene, JA and abscisic acid response genes in the iqd1-1 line. Moreover, quantification of SA, JA, and abscisic acids in IQD1 ^OXP and iqd1-1 lines relative to the wild type, showed a significant reduction in endogenous JA levels in the knockout line, simultaneously with increased SA levels. Relations between IQD1 ^OXP and mutants defective in plant-hormone response indicated that IQD1 cannot rescue the absence of NPR1 or impaired SA accumulation in the NahG line. IQD1 cannot rescue ein2 or eto1 mutations connected to the ethylene pathway involved in both defense responses against B. cinerea and in regulating GS accumulation. Furthermore, IQD1cannot rescue the aos, coi1 or jar1mutations, all involved in the defense response against B. cinerea and it depends on JAR1 to control indole glucosinolate accumulation. We also found that in the B. cinerea, which infected the iqd1-1 mutant, the most abundant upregulated group of proteins is involved in the degradation of complex carbohydrates, as correlated with the sensitivity of this mutant. In summary, our results suggest that IQD1 is an important A. thaliana defensive protein against B. cinerea that is integrated into several important pathways, such as those involved in plant defense and hormone responses.

Ozone responses in Arabidopsis: beyond stomatal conductance

Tropospheric ozone (O3) is a major air pollutant that decreases yield of important crops worldwide. Despite long-lasting research of its negative effects on plants, there are many gaps in our knowledge on how plants respond to O3. In this study, we used natural variation in the model plant Arabidopsis (Arabidopsis thaliana) to characterize molecular and physiological mechanisms underlying O3 sensitivity. A key parameter in models for O3 damage is stomatal uptake. Here we show that the extent of O3 damage in the sensitive Arabidopsis accession Shahdara (Sha) does not correspond with O3 uptake, pointing toward stomata-independent mechanisms for the development of O3 damage. We compared tolerant (Col-0) versus sensitive accessions (Sha, Cvi-0) in assays related to photosynthesis, cell death, antioxidants, and transcriptional regulation. Acute O3 exposure increased cell death, development of lesions in the leaves, and decreased photosynthesis in sensitive accessions. In both Sha and Cvi-0, O3-induced lesions were associated with decreased maximal chlorophyll fluorescence and low quantum yield of electron transfer from Photosystem II to plastoquinone. However, O3-induced repression of photosynthesis in these two O3-sensitive accessions developed in different ways. We demonstrate that O3 sensitivity in Arabidopsis is influenced by genetic diversity given that Sha and Cvi-0 developed accession-specific transcriptional responses to O3. Our findings advance the understanding of plant responses to O3 and set a framework for future studies to characterize molecular and physiological mechanisms allowing plants to respond to high O3 levels in the atmosphere as a result of high air pollution and climate change.