Structural characterization of a putative chitin synthase gene in Phytophthora spp. and analysis of its transcriptional activity during pathogenesis on potato and soybean plants

Integrative RNA-Seq analysis of Capsicum annuum L.-Phytophthora capsici L. pathosystem reveals molecular cross-talk and activation of host defence response

Chili pepper (Capsicum annuum L.) is economically one of the most important spice. But, it's productivity is highly affected by the pathogen, Phytophthora capsici L. Our current understanding of the molecular mechanisms associated with the defence response in C. annuum-P. capsici pathosystem is limited. The current study used RNA-seq technology to dissect the genes associated with defence response against P. capsici infection in two contrasting landraces, i.e. GojamMecha_9086 (Resistant) and Dabat_80045 (Susceptible) exposed to P. capsici infection. The transcriptomes from four leaf samples (RC, RI, SC and SI) of chili pepper resulted in a total of 118,879 assembled transcripts along with 52,384 pooled unigenes. The enrichment analysis of the transcripts indicated 23 different KEGG pathways under five main categories. Out of 774 and 484 differentially expressed genes (DEGs) of two landraces (under study), respectively, 57 and 29 DEGs were observed as associated with defence responses against P. capsici infection in RC vs. RI and SC vs. SI leaf samples, respectively. qRT-PCR analysis of six randomly selected genes validated the results of Illumina NextSeq500 sequencing. A total of 58 transcription factor families (bHLH most abundant) and 2095 protein families (Protein kinase most abundant) were observed across all the samples with maximum hits in RI and SI samples. Expression analysis revealed differential regulation of genes associated with defence and signalling response with shared coordination of molecular function, cellular component and biological processing. The results presented here would enhance our present understanding of the defence response in chili pepper against P. capsici infection, which the molecular breeders could utilize to develop resistant chili genotypes.

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The online version contains supplementary material available at 10.1007/s12298-021-01122-y.

Game-changing alternatives to conventional fungicides: small RNAs and short peptides

Fungicide use is one of the core elements of intensive agriculture because it is necessary to fight pathogens that would otherwise cause large production losses. Oomycete and fungal pathogens are kept under control using several active compounds, some of which are predicted to be banned in the near future owing to serious concerns about their impact on the environment, non-targeted organisms, and human health. To avoid detrimental repercussions for food security, it is essential to develop new biomolecules that control existing and emerging pathogens but are innocuous to human health and the environment. This review presents and discusses the use of novel low-risk biological compounds based on small RNAs and short peptides that are attractive alternatives to current contentious fungicides.

Late blight in tomato: insights into the pathogenesis of the aggressive pathogen Phytophthora infestans and future research priorities

This review provides insights into the molecular interactions between Phytophthora infestans and tomato and highlights research gaps that need further attention. Late blight in tomato is caused by the oomycota hemibiotroph Phytophthora infestans, and this disease represents a global threat to tomato farming. The pathogen is cumbersome to control because of its fast-evolving nature, ability to overcome host resistance and inefficient natural resistance obtained from the available tomato germplasm. To achieve successful control over this pathogen, the molecular pathogenicity of P. infestans and key points of vulnerability in the host plant immune system must be understood. This review primarily focuses on efforts to better understand the molecular interaction between host pathogens from both perspectives, as well as the resistance genes, metabolomic changes, quantitative trait loci with potential for improvement in disease resistance and host genome manipulation via transgenic approaches, and it further identifies research gaps and provides suggestions for future research priorities.

Chitinase Gene Positively Regulates Hypersensitive and Defense Responses of Pepper to Colletotrichum acutatum Infection

Anthracnose caused by Colletotrichum acutatum is one of the most devastating fungal diseases of pepper (Capsicum annuum L.). The utilization of chitin-binding proteins or chitinase genes is the best option to control this disease. A chitin-binding domain (CBD) has been shown to be crucial for the innate immunity of plants and activates the hypersensitive response (HR). The CaChiIII7 chitinase gene has been identified and isolated from pepper plants. CaChiIII7 has repeated CBDs that encode a chitinase enzyme that is transcriptionally stimulated by C. acutatum infection. The knockdown of CaChiIII7 in pepper plants confers increased hypersensitivity to C. acutatum, resulting in its proliferation in infected leaves and an attenuation of the defense response genes CaPR1, CaPR5, and SAR8.2 in the CaChiIII7-silenced pepper plants. Additionally, H₂O₂ accumulation, conductivity, proline biosynthesis, and root activity were distinctly reduced in CaChiIII7-silenced plants. Subcellular localization analyses indicated that the CaChiIII7 protein is located in the plasma membrane and cytoplasm of plant cells. The transient expression of CaChiIII7 increases the basal resistance to C. acutatum by significantly expressing several defense response genes and the HR in pepper leaves, accompanied by an induction of H₂O₂ biosynthesis. These findings demonstrate that CaChiIII7 plays a prominent role in plant defense in response to pathogen infection.

Identification and Characterization of the Chitin Synthase Genes From the Fish Pathogen Saprolegnia parasitica

Saprolegnia parasitica is a pathogenic oomycete responsible for severe fish infections. Despite its low abundance in the cell wall of S. parasitica, chitin is essential for hyphal growth as the inhibition of its biosynthesis leads to highly reduced growth. Here we identified and characterized chitin synthases (CHS) from S. parasitica as potential targets for anti-oomycete drugs. Bioinformatics analyses allowed the identification of six different putative Chs genes in the genome of the pathogen. The total number of genes was confirmed by Southern blot analysis and their expression levels were determined by quantitative PCR. Four of the six Chs genes were expressed in the mycelium, while the two others exhibited undetectable levels of expression. The mycelium was highly sensitive to the addition of nikkomycin Z (NZ) in the culture medium, which led to a decreased amount of chitin in the cell wall by up to 40% in the conditions tested, and to the formation of abnormal branching structures in the hyphae. The presence of NZ increased the expression level of one of the genes, Chs3, suggesting that the corresponding product is compensating the disruption of chitin biosynthesis in the hyphae. In addition, the activity of isolated CHS was strongly inhibited by NZ in vitro. Altogether our data indicate the importance of CHS for the vegetative growth of S. parasitica and demonstrate that these enzymes represent promising targets for the control of diseases caused by oomycetes.

Increased expression of Phytophthora sojae genes encoding membrane-degrading enzymes appears to suggest an early onset of necrotrophy during Glycine max infection

Phytophthora sojae is an oomycete pathogen that causes root, stem, and leaf rot in soybean plants, frequently leading to massive economic losses. Despite its importance, the mechanism by which P. sojae penetrates the host is not yet fully understood. Evidence indicates that P. sojae is not capable of penetrating the plant cell wall via mechanical force, suggesting that alternative factors facilitate breakdown of the host cell wall and membrane. Members of the carbohydrate esterase (CE) family 10 (carboxylesterases, arylesterases, sterol esterases and acetylcholine esterases, collectively known as CE10), are thought to be important for this penetration process. To gain insight into the potential role of CE10-coding genes in P. sojae pathogenesis, the newly revised version of the P. sojae genome was searched for putative CE10-coding genes, and various bioinformatic analyses were conducted using their amino acid and nucleotide sequences. In addition, in planta infection assays were conducted with P. sojae Race 4 and soybean cultivars Williams and Williams 82, and the transcriptional activity of P. sojae CE10-coding genes was evaluated at different time points during infection. Results suggest that these genes are important for both the biotrophic and necrotrophic stages of the P. sojae infection process and provide molecular evidence for stage distinction during infection progression. Furthermore, bioinformatic analyses have identified several conserved gene and protein sequence features that appear to have a significant impact on observed levels of expression during infection. Results agree with previous reports implicating other carbohydrate-active enzymes in P. sojae infection.

Chitin synthase is involved in vegetative growth, asexual reproduction and pathogenesis of Phytophthora capsici and Phytophthora sojae

Chitin is a structural and functional component of the fungal cell wall and also serves as a pathogen-associated molecular pattern (PAMP) that triggers the innate immune responses of host plants. However, no or very little chitin is found in the fungus-like oomycetes. In Phytophthora spp., the presence of chitin has not been demonstrated so far, although putative chitin synthase (CHS) genes, which encode the enzymes that synthesize chitin, are present in their genomes. Here, we revealed that chitin is present in the zoospores and released sporangia of Phytophthora, and this is most consistent with the transcriptional pattern of PcCHS in Phytophthora capsici and PsCHS1 in Phytophthora sojae. Disruption of the CHS genes indicated that PcCHS and PsCHS1, but not PsCHS2 (which exhibited very weak transcription), have similar functions involved in mycelial growth, sporangial production, zoospore release and the pathogenesis of P. capsici and P. sojae. We also suggest that chitin in the zoospores of P. capsici can act as a PAMP that is recognized by the chitin receptors AtLYK5 or AtCERK1 of Arabidopsis. These results provide new insights into the biological significance of chitin and CHSs in Phytophthora and help with the identification of potential targets for disease control.

Diversity and evolution of chitin synthases in oomycetes (Straminipila: Oomycota)

The oomycetes are filamentous eukaryotic microorganisms, distinct from true fungi, many of which act as crop or fish pathogens that cause devastating losses in agriculture and aquaculture. Chitin is present in all true fungi, but it occurs in only small amounts in some Saprolegniomycetes and it is absent in Peronosporomycetes. However, the growth of several oomycetes is severely impacted by competitive chitin synthase (CHS) inhibitors. Here, we shed light on the diversity, evolution and function of oomycete CHS proteins. We show by phylogenetic analysis of 93 putative CHSs from 48 highly diverse oomycetes, including the early diverging Eurychasma dicksonii, that all available oomycete genomes contain at least one putative CHS gene. All gene products contain conserved CHS motifs essential for enzymatic activity and form two Peronosporomycete-specific and six Saprolegniale-specific clades. Proteins of all clades, except one, contain an N-terminal microtubule interacting and trafficking (MIT) domain as predicted by protein domain databases or manual analysis, which is supported by homology modelling and comparison of conserved structural features from sequence logos. We identified at least three groups of CHSs conserved among all oomycete lineages and used phylogenetic reconciliation analysis to infer the dynamic evolution of CHSs in oomycetes. The evolutionary aspects of CHS diversity in modern-day oomycetes are discussed. In addition, we observed hyphal tip rupture in Phytophthora infestans upon treatment with the CHS inhibitor nikkomycin Z. Combining data on phylogeny, gene expression, and response to CHS inhibitors, we propose the association of different CHS clades with certain developmental stages.

Large-scale additive manufacturing with bioinspired cellulosic materials

Cellulose is the most abundant and broadly distributed organic compound and industrial by-product on Earth. However, despite decades of extensive research, the bottom-up use of cellulose to fabricate 3D objects is still plagued with problems that restrict its practical applications: derivatives with vast polluting effects, use in combination with plastics, lack of scalability and high production cost. Here we demonstrate the general use of cellulose to manufacture large 3D objects. Our approach diverges from the common association of cellulose with green plants and it is inspired by the wall of the fungus-like oomycetes, which is reproduced introducing small amounts of chitin between cellulose fibers. The resulting fungal-like adhesive material(s) (FLAM) are strong, lightweight and inexpensive, and can be molded or processed using woodworking techniques. We believe this first large-scale additive manufacture with ubiquitous biological polymers will be the catalyst for the transition to environmentally benign and circular manufacturing models.