Search Results (6)

Tomato is among the most widely traded and consumed vegetables throughout the world; however, it is highly vulnerable to infection by the fungus Alternaria alternata. Fungal elicitors such as chitin oligomers have been shown to trigger the plant’s immune response, protecting the plant against pathogen attacks. Signaling molecules such as ethylene (Et), jasmonic acid (JA), and salicylic acid (SA) are key players in this immune response; however, it is unknown whether fungal chitin oligomers induce the production of these molecules. This study aimed to assess the effect of chitin oligomers isolated from the biomass of the A. alternata on the production of Et, JA, and SA in tomato fruits, as well as the expression of genes encoding transcription factors related with the signaling of Et (SlERF1), JA (SlMYC2), and SA (SlWRKY31). Low-molecular weight chitin oligomers were obtained from A. alternata. The results showed that SlMYC2 involved in JA signaling and production was the first gene induced by chitin oligomers 0.5 h post treatment. Furthermore, after 6 h, a second increase in gene expression was observed. However, SlERF1 involved in Et signaling increased 1 h post treatment and was highly correlated with high expression levels of the SlMYC2 gene, suggesting a strong relationship between Et and JA signaling. The most significant increase in gene expression was observed in SlWRKY31 involved in SA signaling 6 h post treatment with chitin oligomers, which showed a high correlation with Et production. It is concluded that the chitin oligomers of A. alternata elicit an early response in the production of Et, JA, and SA in tomato fruit, which play an important role as signaling molecules in the activation of plant defense mechanisms. Full article

The tomato is an economically important crop worldwide, although fungal infections by Alternaria alternata are the main cause of large postharvest fruit losses. One alternative to chemical control is the induction of the defense mechanism of plants with natural molecules such as chitin. Chitin is a polysaccharide of the fungal cell wall that is recognized by plasma membrane receptors that activates the transcription of plant defense genes. Because there is little information on the genes involved in chitin perception and defense responses to fungal chitin oligomers in tomato fruits, the main objective of this study was to identify pattern recognition receptor-associated genes in tomato fruits that perceive chitin oligomers from the necrotrophic fungus A. alternata using RNA-Seq. Chitin oligomers were obtained from A. alternata via enzymatic treatment. Tomato fruits in the pink ripening stage were exposed to these chitin oligomers for 30 min. The induction of tomato genes encoding a plasma membrane receptor that recognizes fungal chitin (LRR, RLK, SlLYK4, and SlCERK1) was observed 30 min after treatment. Similarly, the perception of Alternaria chitin oligomers triggered the induction of genes involved in signaling pathways regulated by ethylene and jasmonic acid. Further, activation of plant defense phenomena was confirmed by the upregulation of several genes encoding pathogenesis-related proteins. The scientific information generated in the present work will help to better elucidate tomato fruit’s response to pathogens and to design protocols to reduce postharvest losses due to fungal infection. Full article

Fungal pathogens are significant plant-destroying microorganisms that present an increasing threat to the world’s crop production. Chitin is a crucial component of fungal cell walls and a conserved MAMP (microbe-associated molecular pattern) that can be recognized by specific plant receptors, activating chitin-triggered immunity. The molecular mechanisms underlying the perception of chitin by specific receptors are well known in plants such as rice and Arabidopsis thaliana and are believed to function similarly in many other plants. To become a plant pathogen, fungi have to suppress the activation of chitin-triggered immunity. Therefore, fungal pathogens have evolved various strategies, such as prevention of chitin digestion or interference with plant chitin receptors or chitin signaling, which involve the secretion of fungal proteins in most cases. Since chitin immunity is a very effective defensive response, these fungal mechanisms are believed to work in close coordination. In this review, we first provide an overview of the current understanding of chitin-triggered immune signaling and the fungal proteins developed for its suppression. Second, as an example, we discuss the mechanisms operating in fungal biotrophs such as powdery mildew fungi, particularly in the model species Podosphaera xanthii, the main causal agent of powdery mildew in cucurbits. The key role of fungal effector proteins involved in the modification, degradation, or sequestration of immunogenic chitin oligomers is discussed in the context of fungal pathogenesis and the promotion of powdery mildew disease. Finally, the use of this fundamental knowledge for the development of intervention strategies against powdery mildew fungi is also discussed. Full article

Chitin is the main component of fungal cell walls, which can be recognized by pattern recognition receptors (PRRs) as pathogen-associated molecular patterns (PAMP). Chitinase in filamentous fungi has been reported to degrade immunogenic chitin oligomers, thereby preventing chitin-induced immune activation. In this study, we identified the chitinase families in 10 fungal genomes. A total of 131 chitinase genes were identified. Among the chitinase families, 16 chitinase genes from Puccinia striiformis f. sp. tritici (Pst) were identified, and the expression of PstChia1 was the highest during Pst infection. Further studies indicated that PstChia1 is highly induced during the early stages of the interaction of wheat and Pst and has chitinase enzyme activity. The silencing of PstChia1 revealed that PstChia1 limited the growth and reduced the virulence of Pst. The expression level of TaPR1 and TaPR2 was induced in PstChia1 knockdown plants, suggesting that PstChia1 is involved in regulating wheat resistance to Pst. Our data suggest that PstChia1 contributes to pathogenicity by interfering with plant immunity and regulating the growth of Pst. Full article

Phytopathogenic fungi have evolved mechanisms to manipulate plant defences, such as chitin-triggered immunity, a plant defensive response based on the recognition of chitin oligomers by plant-specific receptors. To cope with chitin resistance, fungal pathogens have developed different strategies to prevent chitin recognition, such as binding, breaking, or modifying immunogenic oligomers. In powdery mildew fungi, the activity of chitin deacetylase (CDA) is crucial for this purpose, since silencing of the CDA gene leads to a rapid activation of chitin signalling and the subsequent suppression of fungal growth. In this work, we have identified an unusually short CDA transcript in Podosphaera xanthii, the cucurbit powdery mildew pathogen. This transcript, designated PxCDA3, appears to encode a truncated version of CDA resulting from an alternative splicing of the PxCDA gene, which lacked most of the chitin deacetylase activity domain but retained the carbohydrate-binding module. Experiments with the recombinant protein showed its ability to bind to chitin oligomers and prevent the activation of chitin signalling. Furthermore, the use of fluorescent fusion proteins allowed its localization in plant papillae at pathogen penetration sites. Our results suggest the occurrence of a new fungal chitin-binding effector, designated CHBE, involved in the manipulation of chitin-triggered immunity in powdery mildew fungi. Full article

Wheat is a highly relevant crop worldwide, and like other massive crops, it is susceptible to foliar diseases, which can cause devastating losses. The current strategies to counteract wheat diseases include global monitoring of pathogens, developing resistant genetic varieties, and agrochemical applications upon diseases’ appearance. However, the suitability of these strategies is far from permanent, so other alternatives based on the stimulation of the plants’ systemic responses are being explored. Plants’ defense mechanisms can be elicited in response to the perception of molecules mimicking the signals triggered upon the attack of phytopathogens, such as the release of plant and fungal cell wall-derived oligomers, including pectin and chitin derivatives, respectively. Among the most studied cell wall-derived bioelicitors, oligogalacturonides and oligochitosans have received considerable attention in recent years due to their ability to trigger defense responses and enhance the synthesis of antipathogenic compounds in plants. Particularly, in wheat, the application of bioelicitors induces lignification and accumulation of polyphenolic compounds and increases the gene expression of pathogenesis-related proteins, which together reduce the severity of fungal infections. Therefore, exploring the use of cell wall-derived elicitors, known as oligosaccharins, stands as an attractive option for the management of crop diseases by improving plant readiness for responding promptly to potential infections. This review explores the potential of plant- and fungal-derived oligosaccharins as a practical means to be implemented in wheat crops. Full article