Ethylene emitted by viral pathogen-infected pepper (Capsicum annuum L.) plants is a volatile chemical cue that attracts aphid vectors

Harnessing plant growth-promoting bacteria to combat watermelon mosaic virus in squash

Plant diseases significantly threaten global food security, with viral infections, particularly Watermelon Mosaic Virus (WMV), causing substantial losses in economically important crops such as squash. This study aims to investigate the efficacy of beneficial bacteria isolated from various plants in promoting growth and mitigating the effects of WMV in squash. Understanding the interactions between plants and beneficial microbes could provide sustainable solutions for managing viral infections in agriculture. Sixty-two bacterial isolates were obtained from the rhizosphere of basil, mint, thyme, and squash plants. Among these, six strains exhibited notable plant growth-promoting activities, including the synthesis of indole acetic acid, solubilization of phosphate and zinc, ammonia production, and activity of 1-aminocyclopropane-1-carboxylate deaminase (ACCD). Morphological observations and 16S rRNA gene sequencing identified these isolates as Pseudomonas indica, Bacillus paramycoides, Bacillus thuringiensis, Bacillus mycoides, Paenibacillus glucanolyticus, and Niallia circulans. In pot experiments, squash plants inoculated with these bacterial strains demonstrated significant reductions in disease severity after being infected with WMV. Specifically, foliar applications of the bacteria resulted in the following reductions in disease severity: B. mycoides (87%), B. thuringiensis (73%), Paenibacillus glucanolyticus (73%), Niallia circulans (70%), B. paramycoides (65%), and Pseudomonas indica (65%). Additionally, plants treated with B. mycoides showed increased plant height and shoot dry weight, indicating enhanced growth performance relative to infected controls. Statistical analysis revealed that these growth promotions and disease severity reduction were significant (p < 0.05). GC-MS analysis of the six bacterial strains revealed a diverse array of 73 chemical metabolites, including common compounds such as 9-Octadecenoic acid (Z), benzene derivatives, and cyclopentanones. These findings suggest shared metabolic pathways among the strains and indicate potential roles in ecological interactions, plant defense mechanisms, and antiviral properties. These metabolites likely contribute to the observed reductions in viral severity and enhance plant resilience. The study indicates that inoculating squash plants with specific beneficial bacteria, especially B. mycoides, through foliar or soil application can significantly decrease the severity of WMV and promote plant growth. This approach offers an environmentally friendly alternative to chemical antiviral treatments and may reduce reliance on pesticides. This research highlights the potential of using plant growth-promoting bacteria (PGPB)as a sustainable approach to control viral infections in crops. Further field trials are necessary to PGPB validate the scalability of these findings and assess their effectiveness under diverse agricultural conditions. Incorporating these beneficial microbes into agricultural practices could enhance the resilience of cropping systems, ultimately fostering sustainable agriculture and enhancing food security.

Small non-coding satellite RNAs - the 'game changers' at the virus-host plant interaction?

Satellite RNAs (satRNAs) are RNA molecules associated with many plant viruses and fully dependent on them for replication, encapsidation, and movement within the plant or transmission from plant to plant. Their classification is based on their length, functional protein-coding capacity, and RNA structure (whether linear or circular). They have been of interest for a long time as some of them, in particular systems, cause significant changes in the pathogenesis and epidemiology of plant viruses. The outcomes of how satRNAs affect pathogenesis depend on the components of the pathosystem: host plant species or variety, virus species or even strain, and the sequence of satRNA. These can be additionally affected by biotic and abiotic factors, for example, environmental conditions such as the presence of their vectors or ambient temperature. satRNAs may interfere with primary metabolism, signalling, plant defence [including post-transcriptional gene silencing (PTGS)], as well as the efficiency of virus transmission from plant to plant. In recent years, due to wider access to high-throughput technologies and the extension of studies on satRNAs to include the involvement of external factors in plant-virus-satRNA systems, we are gaining a broader view of the consequences of the presence of these small molecules in viral infections. This review presents the state of the art of satRNA interactions with the helper virus and host plant as well as the influence of satRNAs on the insect vector's behaviour. Moreover, areas requiring further research are identified and knowledge gaps indicated.

Unveiling exogenous potential of phytohormones as sustainable arsenals against plant pathogens: molecular signaling and crosstalk insights

Plants frequently confront pathogens that disrupt physiological and molecular functions, ultimately reducing agricultural yields. To counter these challenges, plants activate sophisticated defense mechanisms to recognize stress signals while optimizing growth. Phytohormones signaling pathways and their crosstalk are central to regulating plant growth, development and defense. Numerous proteins associated with phytohormone signaling pathways have been identified, including receptors for several vital hormones. Previous studies indicate that defense phytohormones, like salicylic acid (SA), jasmonic acid (JA) and ethylene (ET), are crucial to pathogen defense. SA specifically mediates systemic acquired resistance against biotrophic pathogens, while induced systemic resistance relies on JA and ET signaling in response to necrotrophic pathogens. Other hormones, typically associated with growth and development, such as ethylene, abscisic acid, brassinosteroids, melatonin, gibberellins, auxin, and cytokinin, also interact in a complex network of synergistic and antagonistic relationships with defense phytohormones. Moreover, they can achieve effects that surpass conventional pathogen control methods, suggesting their potential as exogenous biocontrol agents. During the past decade, our knowledge of hormone signaling and stress response has become immense. Thus, this review is an attempt to summarize some of the advances in plant signaling and crosstalk mechanisms as well as their potential to be a future arsenal in biotic stress mitigation strategies. Ultimately, this work emphasizes using exogenous phytohormones as a viable alternative for controlling pathogens to enhance crop productivity in pathogen-affected regions.

Effect of ethylene production by four pathogenic fungi on the postharvest diseases of green pepper (Capsicum annuum L.)

Ethylene produced by plants generally induces ripening and promotes decay, whereas the effect of ethylene produced by pathogens on plant diseases remains unclear. In this study, four ethylene-producing fungi including Alternaria alternata (A. alternata, Aa), Fusarium verticilliodes (F. verticillioides, Fv), Fusarium fujikuroi 1 (F. fujikuroi 1, Ff-1) and Fusarium fujikuroi 2 (F. fujikuroi 2, Ff-2) were severally inoculated in potato dextrose broth (PDB) media and postharvest green peppers, the ethylene production rates, disease indexes and chlorophyll fluorescence parameters were determined. The results showed that Ff-2 and Fv in the PDB media had the highest and almost the same ethylene production rates. After inoculation with green peppers, Ff-2 treated group still exhibited the highest ethylene production rate, whereas Aa treated group had a weak promotion effect on ethylene production. Moreover, the ethylene production rate of green peppers with mechanical injury was twice that without mechanical injury, and the ethylene production rates of green peppers treated with Aa, Ff-1, Ff-2 and Fv were 1.2, 2.6, 3.8 and 2.8 folds than those of green peppers without treatment, respectively. These results indicated that pathogen infection stimulated the synthesis of ethylene in green peppers. Correlation analysis indicated that the degreening of Fusarium-infected green pepper was significantly positively correlated with the ethylene production rate of green pepper, whereas the disease spot of Aa-infected green pepper had a significant positive correlations with the ethylene production rate of green peppers. Chlorophyll fluorescence results showed that the green peppers already suffered from severe disease after being infected with fungi for 4 days, and Fusarium infection caused early and serious stress, while the harm caused by A. alternata was relatively mild at the early stage. Our results clearly showed that α-keto-γ-methylthiobutyric acid (KMBA)-mediated ethylene synthesis was the major ethylene synthesis pathway in the four postharvest pathogenic fungi. All the results obtained suggested that ethylene might be the main infection factor of Fusarium spp. in green peppers. For pathogenic fungi, stimulating green peppers to produce high level of ethylene played a key role in the degreening of green peppers.

Rice volatile compound (E)-β-caryophyllene induced by rice dwarf virus (RDV) attracts the natural enemy Cyrtorhinus lividipennis to prey on RDV insect vectors

BACKGROUND

Rice dwarf virus (RDV)-induced rice plant volatiles (E)-β-caryophyllene and 2-heptanol modulate the olfactory behavior of RDV insect vectors that promote viral acquisition and transmission. However, it remains elusive whether these two volatiles could influence the behaviors of the natural enemies of RDV insect vectors. Herein, we determined the effects of these two volatiles on the olfactory and predatory behaviors of Cyrtorhinus lividipennis (Hemiptera: Miridae), an important predator of RDV insect vectors in rice paddies.

RESULTS

The results showed that C. lividipennis preferred RDV-infected rice plant odors over RDV-free rice plant odors. C. lividipennis was attracted by (E)-β-caryophyllene, but showed no behavioral responses to 2-heptanol. The attraction of (E)-β-caryophyllene towards C. lividipennis was further confirmed using oscas1 rice plants, which do not release (E)-β-caryophyllene in response to RDV infection, through a series of complementary assays. The oviposition preference of the RDV vector insect Nephotettix cincticeps (Hemiptera: Cicadellidae) showed no significant difference between RDV-infected and RDV-free wild-type plants, nor between oscas1-RDV and oscas1 plants. However, the predation rate of C. lividipennis for N. cincticeps eggs on RDV-infected plants was higher than that on RDV-free plants, whereas there was no significant difference between oscas1-RDV and oscas1 plants.

CONCLUSION

(E)-β-caryophyllene induced by RDV attracted more C. lividipennis to prey on N. cincticeps eggs and played a crucial role in plant-virus-vector-enemy interactions. These novel findings will promote the design of new strategies for disease control by controlling the populations of insect vectors, for example recruiting more natural enemies by virus-induced plant volatiles. © 2023 Society of Chemical Industry.

Visual tracking of viral infection dynamics reveals the synergistic interactions between cucumber mosaic virus and broad bean wilt virus 2

Cucumber mosaic virus (CMV) is one of the most prevalent plant viruses in the world, and causes severe damage to various crops. CMV has been studied as a model RNA virus to better understand viral replication, gene functions, evolution, virion structure, and pathogenicity. However, CMV infection and movement dynamics remain unexplored due to the lack of a stable recombinant virus tagged with a reporter gene. In this study, we generated a CMV infectious cDNA construct tagged with a variant of the flavin-binding LOV photoreceptor (iLOV). The iLOV gene was stably maintained in the CMV genome after more than four weeks of three serial passages between plants. Using the iLOV-tagged recombinant CMV, we visualized CMV infection and movement dynamics in living plants in a time course manner. We also examined whether CMV infection dynamics is influenced by co-infection with broad bean wilt virus 2 (BBWV2). Our results revealed that no spatial interference occurred between CMV and BBWV2. Specifically, BBWV2 facilitated the cell-to-cell movement of CMV in the upper young leaves. In addition, the BBWV2 accumulation level increased after co-infection with CMV.

Virus-Induced Plant Volatiles Promote Virus Acquisition and Transmission by Insect Vectors

Rice dwarf virus (RDV) is transmitted by insect vectors Nephotettix virescens and Nephotettix cincticeps (Hemiptera: Cicadellidae) that threatens rice yield and results in substantial economic losses. RDV induces two volatiles ((E)-β-caryophyllene (EBC) and 2-heptanol) to emit from RDV-infected rice plants. However, the effects of the two volatiles on the olfactory behavior of both non-viruliferous and viruliferous N. virescens are unknown, and whether the two volatiles could facilitate the spread and dispersal of RDV remains elusive. Combining the methods of insect behavior, chemical ecology, and molecular biology, we found that EBC and 2-heptanol influenced the olfactory behavior of non-viruliferous and viruliferous N. virescens, independently. EBC attracted non-viruliferous N. virescens towards RDV-infected rice plants, promoting virus acquisition by non-viruliferous vectors. The effect was confirmed by using oscas1 mutant rice plants (repressed EBC synthesis), but EBC had no effects on viruliferous N. virescens. 2-heptanol did not attract or repel non-viruliferous N. virescens. However, spraying experiments showed that 2-heptanol repelled viruliferous N. virescens to prefer RDV-free rice plants, which would be conducive to the transmission of the virus. These novel results reveal that rice plant volatiles modify the behavior of N. virescens vectors to promote RDV acquisition and transmission. They will provide new insights into virus-vector-plant interactions, and promote the development of new prevention and control strategies for disease management.