Functional analysis of an α-1,2-mannosidase from Magnaporthe oryzae

The Functional Characterization of Podosphaera xanthii Candidate Effector Genes Reveals Novel Target Functions for Fungal Pathogenicity

Podosphaera xanthii is the main causal agent of powdery mildew disease in cucurbits. In a previous study, we determined that P. xanthii expresses approximately 50 Podosphaera effector candidates (PECs), identified based on the presence of a predicted signal peptide and the absence of functional annotation. In this work, we used host-induced gene silencing (HIGS), employing Agrobacterium tumefaciens as a vector for the delivery of the silencing constructs (ATM-HIGS), to identify genes involved in early plant-pathogen interaction. The analysis of seven selected PEC-encoding genes showed that six of them, PEC007, PEC009, PEC019, PEC032, PEC034, and PEC054, are required for P. xanthii pathogenesis, as revealed by reduced fungal growth and increased production of hydrogen peroxide by host cells. In addition, protein models and protein-ligand predictions allowed us to identify putative functions for these candidates. The biochemical activities of PEC019, PEC032, and PEC054 were elucidated using their corresponding proteins expressed in Escherichia coli. These proteins were confirmed as phospholipid-binding protein, α-mannosidase, and cellulose-binding protein. Further, BLAST searches showed that these three effectors are widely distributed in phytopathogenic fungi. These results suggest novel targets for fungal effectors, such as host-cell plasma membrane, host-cell glycosylation, and damage-associated molecular pattern-triggered immunity.

In vitro secretomic analysis identifies putative pathogenicity-related proteins of Sporisorium scitamineum - The sugarcane smut fungus

Sporisorium scitamineum, the sugarcane smut pathogen, relies predominantly on its secretome to successfully colonise its host, in accordance with other related smut fungi. Considering the significance of deciphering its secretome, we have examined alterations in the in vitro secretome of S. scitamineum in response to synthetic and sugarcane meristem tissue-amended growth media, so as to identify host signal responsive secretory proteins. Secretory proteins that were differentially abundant and exclusively secreted in response to host extract media were identified by two-dimensional gel electrophoresis coupled with MALDI-TOF/TOF MS. Of the 16 differentially abundant and exclusively secreted proteins, nine proteins were identified. Among which, six were related to cell wall modification, morphogenesis, polysaccharide degradation, and carbohydrate metabolism. In planta gene expression profiling indicated that five in vitro secreted proteins were expressed in distinct patterns by S. scitamineum during different stages of infection with relatively higher expression at 1 day after inoculation, suggesting that these proteins could be aiding S. scitamineum at early time points in penetration and colonisation of sugarcane cells. The present study has provided insights into the alterations occurring in the secretome of S. scitamineum at in vitro conditions and has resulted in the identification of secretory proteins that are possibly associated with pathogenicity of the sugarcane smut fungus.

The toxicology mechanism of endophytic fungus and swainsonine in locoweed

Locoweed is a perennial herbaceous plant included in Astragalus spp. and Oxytropis spp. that contains the toxic indolizidine alkaloid swainsonine. The livestock that consume locoweed can suffer from a type of toxicity called locoism. There are aliphaticnitro compounds, selenium, selenium compounds, and alkaloids in locoweed. The toxic component in locoweed has been identified as swainsonine, an indolizidine alkaloid. Swainsonine inhibits lysosomal a-mannosidase and mannosidase II, resulting in altered oligosaccharide degradation and incomplete glycoprotein processing. Corresponding studies on endophytic fungi producing swainsonine have been isolated from a variety of locoweed, and these endophytic fungi and locoweed have a close relationship. Endophytic fungi can promote the growth of locoweed and increase swainsonine production. As a result, livestock that consume locoweed exhibit several symptoms, including dispirited behavior, staggering gait, chromatopsia, trembling, ataxia, and cellular vacuolar degeneration of most tissues by pathological observation. Locoism results in significant annual economic losses. Therefore, in this paper, we review the current research on locoweed, including that on locoweed species distribution in China, endophyte fungus in locoweed, the toxicology mechanism of locoweed, and the swainsonine effect on reproduction.

Comparisons of Ribosomal Protein Gene Promoters Indicate Superiority of Heterologous Regulatory Sequences for Expressing Transgenes in Phytophthora infestans

Molecular genetics approaches in Phytophthora research can be hampered by the limited number of known constitutive promoters for expressing transgenes and the instability of transgene activity. We have therefore characterized genes encoding the cytoplasmic ribosomal proteins of Phytophthora and studied their suitability for expressing transgenes in P. infestans. Phytophthora spp. encode a standard complement of 79 cytoplasmic ribosomal proteins. Several genes are duplicated, and two appear to be pseudogenes. Half of the genes are expressed at similar levels during all stages of asexual development, and we discovered that the majority share a novel promoter motif named the PhRiboBox. This sequence is enriched in genes associated with transcription, translation, and DNA replication, including tRNA and rRNA biogenesis. Promoters from the three P. infestans genes encoding ribosomal proteins S9, L10, and L23 and their orthologs from P. capsici were tested for their ability to drive transgenes in stable transformants of P. infestans. Five of the six promoters yielded strong expression of a GUS reporter, but the stability of expression was higher using the P. capsici promoters. With the RPS9 and RPL10 promoters of P. infestans, about half of transformants stopped making GUS over two years of culture, while their P. capsici orthologs conferred stable expression. Since cross-talk between native and transgene loci may trigger gene silencing, we encourage the use of heterologous promoters in transformation studies.

Exploring pathogenic mechanisms of Botrytis cinerea secretome under different ambient pH based on comparative proteomic analysis

Botrytis cinerea causes gray mold rot on over 200 plant species worldwide, resulting in great economic loss every year. Cooperation of proteins secreted by B. cinerea plays an important role in its successful infection to host plants. The ambient pH, as one of the most important environmental parameters, can regulate expression of secreted proteins in various fungal pathogens. In the present study, we mainly investigated the effect of ambient pH on secretome of B. cinerea strain B05.10 with a comparative proteomic method based on 2-DE. Distinct differences in secretome of B. cinerea were found between pH 4 and 6 treatments, and 47 differential spots, corresponding to 21 unique proteins, were identified using MALDI-TOF/TOF. At pH 4, more proteins related to proteolysis were induced, whereas most of up-accumulated proteins were cell wall degrading enzymes at pH 6. Analysis of gene expression using quantitative real-time PCR suggests that production of most of these proteins was regulated at the level of transcription. These findings indicate that B. cinerea can adjust protein profile of secretome responding to different ambient pH values and provide evidence to deeply understand the complicated infecting mechanisms of B. cinerea on a wide range of plant hosts.

Identification of the putative specific pathogenic genes of Porphyromonas gingivalis with type II fimbriae

Porphyromonas gingivalis, the key etiologic agent of periodontitis, can be classified into six types (I to V and Ib) based on the fimA genes that encode FimA (a subunit of fimbriae). Accumulated evidence indicates that P. gingivalis expressing Type II fimbriae (Pg-II) is the most frequent isolate from severe periodontitis cases and is more virulent than other types of P. gingivalis. However, during the Pg-II infection process, which specific virulence factors play the key role is still unclear. In this study, we examined the capabilities of three Pg-II strains to invade and modulate the inflammatory cytokine expression of human gingival epithelial cells (GECs) compared to two Pg-I strains. P. gingivalis oligo microarrays were used to compare gene expression profiles of Pg-II strains that invade GECs with Pg-I strains. The differential gene expression of Pg-II was confirmed by quantitative reverse transcription-polymerase chain reaction. Our results showed that all of the Pg-II strains could induce interleukin (IL)-1β and IL-6 secretion significantly when compared to Pg-I strains. Thirty-seven genes that were specifically expressed during the pathogenic process of Pg-II were identified by a microarray assay. These findings provide a new insight at the molecular level to explain the specific pathogenic mechanism of Pg-II strains.