Identification and Characterization of a Novel Protein Disulfide Isomerase Gene (MgPDI2) from Meloidogyne graminicola

Protein Disulfide Isomerase FgEps1 Is a Secreted Virulence Factor in Fusarium graminearum

Protein disulfide isomerase (PDI) is a member of the thioredoxin (Trx) superfamily with important functions in cellular stability, ion uptake, and cellular differentiation. While PDI has been extensively studied in humans and animals, its role in fungi remains relatively unknown. In this study, the biological functions of FgEps1, a disulfide bond isomerase in the fungal pathogen Fusarium graminearum, were investigated. It was found that FgEps1 mutation affected nutritional growth, asexual and sexual reproduction, and stress tolerance. Additionally, its deletion resulted in reduced pathogenicity and impaired DON toxin biosynthesis. The involvement of FgEps1 in host infection was also confirmed, as its expression was detected during the infection period. Further investigation using a yeast signal peptide secretion system and transient expression in Nicotiana benthamiana showed that FgEps1 suppressed the immune response of plants and promoted infection. These findings suggest that virulence factor FgEps1 plays a crucial role in growth, development, virulence, secondary metabolism, and host infection in F. graminearum.

An Insight into Occurrence, Biology, and Pathogenesis of Rice Root-Knot Nematode Meloidogyne graminicola

Rice (Oryza sativa L.) is one of the most widely grown crops in the world, and is a staple food for more than half of the global total population. Root-knot nematodes (RKNs), Meloidogyne spp., and especially M. graminicola, seem to be significant rice pests, which makes them the most economically important plant-parasitic nematode in this crop. RKNs develop a feeding site in galls by causing host cells to differentiate into hypertrophied, multinucleate, metabolically active cells known as giant cells. This grazing framework gives the nematode a constant food source, permitting it to develop into a fecund female and complete its life cycle inside the host root. M. graminicola effector proteins involved in nematode parasitism, including pioneer genes, were functionally characterized in earlier studies. Molecular modelling and docking studies were performed on Meloidogyne graminicola protein targets, such as β-1,4-endoglucanase, pectate lyase, phospholipase B-like protein, and G protein-coupled receptor kinase, to understand the binding affinity of Beta-D-Galacturonic Acid, 2,6,10,15,19,23-hexamethyltetracosane, (2S)-2-amino-3-phenylpropanoic acid, and 4-O-Beta-D-Galactopyranosyl-Alpha-D-Glucopyranose against ligand molecules of rice. This study discovered important molecular aspects of plant-nematode interaction and candidate effector proteins that were regulated by M. graminicola-infected rice plants. To the best of our knowledge, this is the first study to describe M. graminicola's molecular adaptation to host parasitism.

Insights Into the Genetics of the Zhonghua 11 Resistance to Meloidogyne graminicola and Its Molecular Determinism in Rice

Meloidogyne graminicola is a widely spread nematode pest of rice that reduces crop yield up to 20% on average in Asia, with devastating consequences for local and global rice production. Due to the ban on many chemical nematicides and the recent changes in water management practices in rice agriculture, an even greater impact of M. graminicola can be expected in the future, stressing the demand for the development of new sustainable nematode management solutions. Recently, a source of resistance to M. graminicola was identified in the Oryza sativa japonica rice variety Zhonghua 11 (Zh11). In the present study, we examine the genetics of the Zh11 resistance to M. graminicola and provide new insights into its cellular and molecular mechanisms. The segregation of the resistance in F₂ hybrid populations indicated that two dominant genes may be contributing to the resistance. The incompatible interaction of M. graminicola in Zh11 was distinguished by a lack of swelling of the root tips normally observed in compatible interactions. At the cellular level, the incompatible interaction was characterised by a rapid accumulation of reactive oxygen species in the vicinity of the nematodes, accompanied by extensive necrosis of neighbouring cells. The expression profiles of several genes involved in plant immunity were analysed at the early stages of infection during compatible (susceptible plant) and incompatible (resistant plant) interactions. Notably, the expression of OsAtg4 and OsAtg7, significantly increased in roots of resistant plants in parallel with the cell death response, suggesting that autophagy is activated and may contribute to the resistance-mediated hypersensitive response. Similarly, transcriptional regulation of genes involved in hormonal pathways in Zh11 indicated that salicylate signalling may be important in the resistance response towards M. graminicola. Finally, the nature of the resistance to M. graminicola and the potential exploitation of the Zh11 resistance for breeding are discussed.

Effectors of Root-Knot Nematodes: An Arsenal for Successful Parasitism

Root-knot nematodes (RKNs) are notorious plant-parasitic nematodes first recorded in 1855 in cucumber plants. They are microscopic, obligate endoparasites that cause severe losses in agriculture and horticulture. They evade plant immunity, hijack the plant cell cycle, and metabolism to modify healthy cells into giant cells (GCs) - RKN feeding sites. RKNs secrete various effector molecules which suppress the plant defence and tamper with plant cellular and molecular biology. These effectors originate mainly from sub-ventral and dorsal oesophageal glands. Recently, a few non-oesophageal gland secreted effectors have been discovered. Effectors are essential for the entry of RKNs in plants, subsequently formation and maintenance of the GCs during the parasitism. In the past two decades, advanced genomic and post-genomic techniques identified many effectors, out of which only a few are well characterized. In this review, we provide molecular and functional details of RKN effectors secreted during parasitism. We list the known effectors and pinpoint their molecular functions. Moreover, we attempt to provide a comprehensive insight into RKN effectors concerning their implications on overall plant and nematode biology. Since effectors are the primary and prime molecular weapons of RKNs to invade the plant, it is imperative to understand their intriguing and complex functions to design counter-strategies against RKN infection.

A Meloidogyne graminicola Pectate Lyase Is Involved in Virulence and Activation of Host Defense Responses

Plant-parasitic nematodes secrete an array of cell-wall-degrading enzymes to overcome the physical barrier formed by the plant cell wall. Here, we describe a novel pectate lyase gene Mg-PEL1 from M. graminicola. Quantitative real-time PCR assay showed that the highest transcriptional expression level of Mg-PEL1 occurred in pre-parasitic second-stage juveniles, and it was still detected during the early parasitic stage. Using in situ hybridization, we showed that Mg-PEL1 was expressed exclusively within the subventral esophageal gland cells of M. graminicola. The yeast signal sequence trap system revealed that it possessed an N-terminal signal peptide with secretion function. Recombinant Mg-PEL1 exhibited hydrolytic activity toward polygalacturonic acid. Rice plants expressing RNA interference vectors targeting Mg-PEL1 showed an increased resistance to M. graminicola. In addition, using an Agrobacterium-mediated transient expression system and plant immune response assays, we demonstrated that the cell wall localization of Mg-PEL1 was required for the activation of plant defense responses, including programmed plant cell death, reactive oxygen species (ROS) accumulation and expression of defense-related genes. Taken together, our results indicated that Mg-PEL1 could enhance the pathogenicity of M. graminicola and induce plant immune responses during nematode invasion into plants or migration in plants. This provides a new insight into the function of pectate lyases in plants-nematodes interaction.