Genes Encoding Cell Wall-degrading Enzymes Research Articles

The Adenylate Cyclase-Encoding Gene crac Is Involved in Clonostachys rosea Mycoparasitism.

Clonostachys rosea is an excellent biocontrol fungus against numerous fungal plant pathogens. The cAMP signaling pathway is a crucial signal transduction pathway in fungi. To date, the role of the cAMP signaling pathway in C. rosea mycoparasitism remains unknown. An adenylate cyclase-encoding gene, crac (an important component of the cAMP signaling pathway), was previously screened from C. rosea 67-1, and its expression level was dramatically upregulated during the C. rosea mycoparasitization of the sclerotia of Sclerotinia sclerotiorum. In this study, the function of crac in C. rosea mycoparasitism was explored through gene knockout and complementation. The obtained results show that the deletion of crac influenced the growth rate and colony morphology of C. rosea, as well as the tolerance to NaCl and H2O2 stress. The mycoparasitic effects on the sclerotia of S. sclerotiorum and the biocontrol capacity on soybean Sclerotinia stem rot in ∆crac-6 and ∆crac-13 were both attenuated compared with that of the wild-type strain and complementation transformants. To understand the regulatory mechanism of crac during C. rosea mycoparasitism, transcriptomic analysis was conducted between the wild-type strain and knockout mutant. A number of biocontrol-related genes, including genes encoding cell wall-degrading enzymes and transporters, were significantly differentially expressed during C. rosea mycoparasitism, suggesting that crac may be involved in C. rosea mycoparasitism by regulating the expression of these DEGs. These findings provide insight for further exploring the molecular mechanism of C. rosea mycoparasitism.

Genome-Wide Characterization Reveals Variation Potentially Involved in Pathogenicity and Mycotoxins Biosynthesis of Fusarium proliferatum Causing Spikelet Rot Disease in Rice.

Fusarium proliferatum is the primary cause of spikelet rot disease in rice (Oryza sativa L.) in China. The pathogen not only infects a wide range of cereals, causing severe yield losses but also contaminates grains by producing various mycotoxins that are hazardous to humans and animals. Here, we firstly reported the whole-genome sequence of F. proliferatum strain Fp9 isolated from the rice spikelet. The genome was approximately 43.9 Mb with an average GC content of 48.28%, and it was assembled into 12 scaffolds with an N50 length of 4,402,342 bp. There is a close phylogenetic relationship between F. proliferatum and Fusarium fujikuroi, the causal agent of the bakanae disease of rice. The expansion of genes encoding cell wall-degrading enzymes and major facilitator superfamily (MFS) transporters was observed in F. proliferatum relative to other fungi with different nutritional lifestyles. Species-specific genes responsible for mycotoxins biosynthesis were identified among F. proliferatum and other Fusarium species. The expanded and unique genes were supposed to promote F. proliferatum adaptation and the rapid response to the host’s infection. The high-quality genome of F. proliferatum strain Fp9 provides a valuable resource for deciphering the mechanisms of pathogenicity and secondary metabolism, and therefore shed light on development of the disease management strategies and detoxification of mycotoxins contamination for spikelet rot disease in rice.

High-CO2 Treatment Prolongs the Postharvest Shelf Life of Strawberry Fruits by Reducing Decay and Cell Wall Degradation

Improved methods are needed to extend the shelf life of strawberry fruits. The objective of this study was to determine the postharvest physiological mechanism of high-CO2 treatment in strawberries. Harvested strawberries were stored at 10 °C after 3 h of exposure to a treatment with 30% CO2 or air. Pectin and gene expression levels related to cell wall degradation were measured to assess the high-CO2 effects on the cell wall and lipid metabolism. Strawberries subjected to high-CO2 treatment presented higher pectin content and firmness and lower decay than those of control fruits. Genes encoding cell wall-degrading enzymes (pectin methylesterase, polygalacturonase, and pectate lyase) were downregulated after high-CO2 treatment. High-CO2 induced the expression of oligogalacturonides, thereby conferring defense against Botrytis cinerea in strawberry fruits, and lowering the decay incidence at seven days after its inoculation. Our findings suggest that high-CO2 treatment can maintain strawberry quality by reducing decay and cell wall degradation.

Genome Sequencing Analysis of Scleromitrula shiraiana, a Causal Agent of Mulberry Sclerotial Disease With Narrow Host Range.

Scleromitrula shiraiana is a necrotrophic fungus with a narrow host range, and is one of the main causal pathogens of mulberry sclerotial disease. However, its molecular mechanisms and pathogenesis are unclear. Here, we report a 39.0 Mb high-quality genome sequence for S. shiraiana strain SX-001. The S. shiraiana genome contains 11,327 protein-coding genes. The number of genes and genome size of S. shiraiana are similar to most other Ascomycetes. The cross-similarities and differences of S. shiraiana with the closely related Sclerotinia sclerotiorum and Botrytis cinerea indicated that S. shiraiana differentiated earlier from their common ancestor. A comparative genomic analysis showed that S. shiraiana has fewer genes encoding cell wall-degrading enzymes (CWDEs) and effector proteins than that of S. sclerotiorum and B. cinerea, as well as many other Ascomycetes. This is probably a key factor in the weaker aggressiveness of S. shiraiana to other plants. S. shiraiana has many species-specific genes encoding secondary metabolism core enzymes. The diversity of secondary metabolites may be related to the adaptation of these pathogens to specific ecological niches. However, melanin and oxalic acid are conserved metabolites among many Sclerotiniaceae fungi, and may be essential for survival and infection. Our results provide insights into the narrow host range of S. shiraiana and its adaptation to mulberries.

Analyses of the Root-Knot Nematode (Meloidogyne graminicola) Transcriptome during Host Infection Highlight Specific Gene Expression Profiling in Resistant Rice Plants

The plant-parasitic nematode Meloidogyne graminicola causes considerable damages to rice (Oryza sativa) culture. Resistance to M. graminicola in the related species Oryza glaberrima reduces root penetration by juveniles and stops further nematode development. M. graminicola genes expressed during O. sativa infection were previously characterized but no information is available about the molecular dialogue established with a resistant plant. We compared the M. graminicola transcriptomes of stage-two juveniles (J2s) before and during infection of susceptible or resistant rice. Among 36,121 M. graminicola genes surveyed, 367 were differentially expressed during infection of resistant or susceptible plants. Genes encoding cell wall-degrading enzymes, peptidases and neuropeptides were expressed for a longer time in resistant plants compared to susceptible plants. Conversely, genes related to nematode development were not activated in the resistant host. The majority of M. graminicola effector genes had similar expression patterns, whatever the host genotype. However, two venom allergen-like protein (VAP)-encoding genes were specifically induced in resistant plants and Mg-VAP1 silencing in J2s reduced their ability to colonize roots. This study highlighted that M. graminicola adapts its gene expression to the host susceptibility. Further investigation is required to assess the role of Mg-VAPs in the rice–nematode interaction.

Integrated transcriptomic-metabolomic analysis reveals cellular responses of harvested strawberry fruit subjected to short-term exposure to high levels of carbon dioxide

Harvested strawberry (Fragaria × ananassa) fruit has a short shelf life due to rapid postharvest metabolism, quick softening, mechanical damage, and fungal decay. To improve the storability of strawberry fruit, we subjected harvested fruit to short-term exposure to 30% carbon dioxide (CO2) and used transcriptomic and metabolomic analyses to identify the cellular responses induced by this treatment. Fruit was stored at 10 °C for 10 d after a 3-h exposure to 30% CO2 (treatment) or ambient air (control) at 25 °C, respectively. The CO2 treatment reduced fruit decay and softening compared to the control throughout the 10-d storage period. Transcriptomic analyses revealed that expression levels of genes encoding cell wall-degrading enzymes (expansin, pectinesterase, and β-xylosidase) decreased in response to the CO2 treatment. Within 1 d after the CO2 treatment, the expression levels of genes encoding heat-shock proteins significantly increased. Metabolite profiling revealed that glucose, quinic acid, and succinic acid increased in responses to the CO2 treatment at 1 d. Transmission electron microscopy showed that disintegration of the middle lamella in the cell wall was inhibited by the CO2 treatment. Polyuronide (insoluble pectin) content in cell walls was 30% higher, on average, in the treated fruit than those in the control fruit during the 10-d storage period. These results indicate that a short-term treatment with 30% CO2 reduces the degradation of pectin in the cell wall by reducing the activity of cell wall-degrading enzymes and induces abiotic stress-response genes in harvested strawberry fruit. Our results improve our understanding of the molecular mechanisms behind CO2-responsive genes in strawberry fruit and provide insight into ways to improve the postharvest quality of strawberries.

Gene expression of cell-wall degrading enzymes in sapodilla (Manilkara zapota) fruit

Sapodilla (Manilkara zapota) is a tropical fruit crop grown commercially in Thailand which undergoes a rapid change after harvest. Information on these postharvest changes is rare. In this work, firmness of the fruit flesh in sapodilla cvv. Makok-Yai and Kra-Suay was observed to sharply decrease and was low by day 5 after harvest. The decrease in fruit firmness was hastened after ethylene treatment, and prevented after treatment with 1-methylcyclopropene. Three genes encoding cell wall-degrading enzymes, an endo- -1,4-glucanase (MzEG), a pectate lyase (MzPL), and a polygalacturonase (MzPG), were isolated. In both cultivars tested, the transcript abundance of the isolated MzEG was correlated with fruit growth and not with loss of fruit firmness after harvest. In contrast, the mRNA of the isolated MzPL and MzPG accumulated during postharvest ripening. Ethylene treatment increased the transcript abundance in both genes. Throughout the treatments the expression of MzPG was well correlated with the decrease of fruit firmness, whereas the expression of MzPL was not. The PG activity in the fruit flesh was also well correlated with the decrease of flesh firmness. Hence the expression of the isolated MzPG was correlated both with PG activity and with firmness. Our data indicated that MzPG plays an important role in the rapid softening of sapodilla fruits during ripening.

Sugars and pH: A clue to the regulation of fungal cell wall-degrading enzymes in plants

In recent years, substantial progress has been made in understanding the role of cell wall-degrading enzymes in virulence of fungal pathogens using genetic tools. A homologous recombination-mediated targeted gene disruption of a single pectolytic gene decreased virulence in multiple fungal pathogens. Furthermore, differential regulation of a gene that encodes a cell wall-degrading enzyme during infection under different host environments has recently been examined, and host pH and sugars are involved in the regulation of the polygalacturonase gene. We will provide a brief overview of the biology of the macerating diseases caused by phytopathogenic Alternaria pathogens in particular hosts, followed by a description of possible mechanisms controlling the differential expression of genes encoding cell wall-degrading enzymes in the infected host.

Antifungal, Synergistic Interaction Between Chitinolytic Enzymes fromTrichoderma harzianumandEnterobacter cloacae

Biocontrol strains from the genera Enterobacter and Pseudomonas and two chitinolytic enzymes from Trichoderma harzianum isolate P1 were combined and tested for antifungal activity in bioassays. Inhibitory effects on spore germination and germ tube elongation of Botrytis cinerea, Fusarium solani, and Uncinula necator were synergistically increased by mixing fungal enzymes and cells of Enterobacter cloacae but not of Pseudomonas spp. Culture filtrate of E. cloacae contained antifungal compounds and produced moderate levels of inhibition, either in plate assays or in bioassays conducted in potato-dextrose broth. However, the combination of bacterial culture filtrate with fungal chitinolytic enzymes generated only an additive response, indicating that the presence of bacterial cells was required for a synergistic effect. Chitinolytic enzyme activity in the presence of chitinous substrates enhanced the growth of E. cloacae and readily restored the ability of bacterial cells to bind to hyphae of the pathogens despite high concentrations of D-glucose or sucrose in the medium. The results of this study suggest that transgenic bacteria, capable of binding to fungal cell walls and expressing fungal genes encoding cell wall-degrading enzymes, may be powerful biocontrol agents