Plant-Parasitic Nematodes and their Effects on Ornamental Plants: A Review.

Worldwide, the ornamental plant industry is estimated to be valued at $70 billion, with the United States' ornamental plant industry valued at $4.8 billion in 2020. Ornamental plants are cultivated for numerous reasons worldwide, such as decorative, medicinal, social, and utility purposes, making the ornamental field a high growth industry. One of the main pathogen groups affecting the yield and growth of the ornamental plant industry is plant-parasitic nematodes, which are microscopic roundworms that feed on plant parts causing significant yield loss. There are many kinds of plant-parasitic nematodes that affect ornamental plants, with the main genera being Meloidogyne spp., Aphelenchoides spp., Paratylenchus spp., Pratylenchus spp., Helicotylenchus spp., Radopholus spp., Xiphinema spp., Trichodorus spp., Paratrichodorus spp., Rotylenchulus spp., and Longidorus spp. The aim of this review is to focus on the effects, hosts, and symptoms of these major plant-parasitic nematodes on ornamental plants and synthesize current management strategies in the ornamental plant industry.

Exploring Machine Learning Algorithms to Unveil Genomic Regions Associated With Resistance to Southern Root-Knot Nematode in Soybeans.

Southern root-knot nematode [SRKN, Meloidogyne incognita (Kofold & White) Chitwood] is a plant-parasitic nematode challenging to control due to its short life cycle, a wide range of hosts, and limited management options, of which genetic resistance is the main option to efficiently control the damage caused by SRKN. To date, a major quantitative trait locus (QTL) mapped on chromosome (Chr.) 10 plays an essential role in resistance to SRKN in soybean varieties. The confidence of discovered trait-loci associations by traditional methods is often limited by the assumptions of individual single nucleotide polymorphisms (SNPs) always acting independently as well as the phenotype following a Gaussian distribution. Therefore, the objective of this study was to conduct machine learning (ML)-based genome-wide association studies (GWAS) utilizing Random Forest (RF) and Support Vector Machine (SVM) algorithms to unveil novel regions of the soybean genome associated with resistance to SRKN. A total of 717 breeding lines derived from 330 unique bi-parental populations were genotyped with the Illumina Infinium BARCSoySNP6K BeadChip and phenotyped for SRKN resistance in a greenhouse. A GWAS pipeline involving a supervised feature dimension reduction based on Variable Importance in Projection (VIP) and SNP detection based on classification accuracy was proposed. Minor effect SNPs were detected by the proposed ML-GWAS methodology but not identified using Bayesian-information and linkage-disequilibrium Iteratively Nested Keyway (BLINK), Fixed and Random Model Circulating Probability Unification (FarmCPU), and Enriched Compressed Mixed Linear Model (ECMLM) models. Besides the genomic region on Chr. 10 that can explain most of SRKN resistance variance, additional minor effects SNPs were also identified on Chrs. 10 and 11. The findings in this study demonstrated that overfitting in GWAS may lead to lower prediction accuracy, and the detection of significant SNPs based on classification accuracy limited false-positive associations. The expansion of the basis of the genetic resistance to SRKN can potentially reduce the selection pressure over the major QTL on Chr. 10 and achieve higher levels of resistance.

Esophageal Gland RNA-Seq Resource of a Virulent and Avirulent Population of the Soybean Cyst Nematode Heterodera glycines.

The soybean cyst nematode Heterodera glycines is the most economically devastating pathogen of soybean in the United States and threatens to become even more damaging through the selection of virulent nematode populations in the field that can overcome natural resistance mechanisms in soybean cultivars. This pathogen, therefore, demands intense transcriptomic/genomic research inquiries into the biology of its parasitic mechanisms. H. glycines delivers effector proteins that are produced in specialized gland cells into the soybean root to enable infection. The study of effector proteins, thus, is particularly promising when exploring novel management options against this pathogen. Here, we announce the availability of a gland cell-specific RNA-seq resource. These data represent an expression snapshot of gland cell activity during early soybean infection of a virulent and an avirulent H. glycines population, providing a unique and highly valuable resource for scientists examining effector biology and nematode virulence.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Resistance Gene Pyramiding and Rotation to Combat Widespread Soybean Cyst Nematode Virulence.

Soybean cyst nematode (SCN) is an important pathogen of soybean causing >$1 billion in yield losses annually in the United States. Planting SCN-resistant soybean cultivars is the primary management strategy. Resistance genes derived from the plant introduction (PI) 88788 (rhg1-b) and PI 548402 (Peking; rhg1-a and Rhg4) are the main types of resistance available in commercial cultivars. The PI 88788 rhg1-b resistance allele is found in the majority of SCN-resistant cultivars in the north central United States. The widespread use of PI 88788 rhg1-b has led to limited options for farmers to rotate resistance sources to manage SCN. Consequently, overreliance on a single type of resistance has resulted in the selection of SCN populations that have adapted to reproduce on these resistant cultivars. Here we evaluated the effectiveness of rotating soybean lines with different combinations of resistance genes to determine the best strategy for combating the widespread increase in virulent SCN and limit future nematode adaptation to resistant cultivars. Eight SCN populations were developed by continuous selection of a virulent SCN field population (Heterodera glycines [HG] type 1.2.5.7) on a single resistance source or in rotation with soybean pyramiding different resistance gene alleles derived from PI 88788 (rhg1-b), PI 437654 (rhg1-a and Rhg4), PI 468916 (cqSCN-006 and cqSCN-007), and PI 567516C (Chr10). SCN population densities were determined for eight generations. HG type tests were conducted after the eighth generation to evaluate population shifts. The continued use of rhg1-b or 006/007 had limited effectiveness for reducing SCN type 1.2.5.7 population density, whereas rotation to the use of rhg1-a/Rhg4 resistance significantly reduced SCN population density but selected for broader SCN virulence (HG type 1.2.3.5.6.7). A rotation of rhg1-a/Rhg4 with a pyramid of rhg1-b/006/007/Chr10 was the most effective combination at both reducing population density and minimizing selection pressure. Our results provide guidance for implementation of a strategic SCN resistance rotation plan to manage the widespread virulence on PI 88788 and sustain the future durability of SCN resistance genes.

Scavenger Receptor Class A to E Involved in Various Cancers.

Scavenger receptors typically bind to multiple ligands on a cell surface, including endogenous and modified host-derived molecules and microbial pathogens. They promote the elimination of degraded or harmful substances such as non-self or altered-self targets through endocytosis, phagocytosis, and adhesion. Currently, scavenger receptors are subdivided into eight classes based on several variations in their sequences due to alternative splicing. Since recent studies indicate targeting scavenger receptors has been involved in cancer prognosis and carcinogenesis, we will focus on the current knowledge about the emerging role of scavenger receptor classes A to E in cancer progression.

Melanoma Cell Death Mechanisms.

Over recent years, several new molecular and immunogenic therapeutic approaches to melanoma treatment have been approved and implemented in clinical practice. Mechanisms of resistance to these new therapies have become a major problem. Mutation-specific pharmacotherapy can result in simultaneous emergence of resistant clones at many separate body sites despite an initially positive therapeutic response. Additionally, treatments aimed at inducing apoptosis are subject to resistance due to escape through other known mechanisms of regulated cell death (RCD). In this review, we discuss the complexity in pharmacological manipulation of melanoma with c-Kit, BRAF, MEK, and/or mTOR mutant cell lines. This study also addresses melanoma evasion of cell death through modalities of RCD such as apoptosis, autophagy, and necroptosis. This study also examines new combination therapies which have been approved to target both cell cycle dysregulation and cell death pathways. Lastly, we recognize the importance of immunomodulation though manipulation of the body's natural killing mechanisms with CTLA4, PD1, and CSF1 inhibition. As we begin to recognize tumor cell activation of alternate pathways, evasion of programmed cell death, and manipulation of the tumor microenvironment, it is increasingly important to grasp the complexity of personalized therapy in melanoma treatment.

Survey of Heterodera glycines Population Densities and Virulence Phenotypes During 2015-2016 in Missouri.

The soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pathogens of soybean. Periodic monitoring of SCN population densities and virulence phenotypes is necessary for developing management strategies utilizing resistant cultivars, the primary strategy used to combat this pest. Therefore, we conducted a statewide survey of Missouri to determine SCN population densities and virulence phenotypes during 2015-2016 and compared these results with a similar survey conducted in 2005. SCN population densities were determined for 393 soil samples representing 74 soybean-producing counties across eight geographical regions of Missouri. Eighty-eight percent of samples tested positive for SCN, up from 50% in 2005, and population densities ranged from 125 to 99,000 eggs per 250 cm3 of soil. The virulence phenotypes of 48 SCN populations also were determined. For this, female indices (FI) were calculated by dividing the mean number of females that develop on the roots of a set of resistant soybean indicator lines by the mean number of females that develop on the roots of susceptible cultivar Lee74 after 30 days in the greenhouse then multiplying by 100 to obtain a percentage. Notably, all SCN populations evaluated during 2015-2016 had a FI > 10 on PI 88788, the most widely used source of resistance in Missouri, in contrast to 78% in 2005. Moreover, 50% of these populations had a FI > 50 on PI 88788, up from 16% in 2005. Forty-three percent of populations tested also had a FI > 10 on Peking, the second most common source of resistance by farmers. Our results show that over the last decade, SCN has become more prevalent in Missouri fields. Additionally, the percentage of individuals within SCN field populations that are virulent on PI 88788 and Peking has markedly increased. The results stress the importance of rotating cultivars with different types of resistance when using resistant cultivars to manage SCN.

The regulation of combined treatment-induced cell death with recombinant TRAIL and bortezomib through TRAIL signaling in TRAIL-resistant cells.

BACKGROUND: Multiple trials have attempted to demonstrate the effective induction of cell death in TRAIL-resistant cancer cells, including using a combined treatment of recombinant TRAIL and various proteasome inhibitors. These studies have yielded limited success, as the mechanism of cell death is currently unidentified. Understanding this mechanism's driving forces may facilitate the induction of cell death in TRAIL-resistant cancer cells. METHODS: Three kinds of recombinant soluble TRAIL proteins were treated into TRAIL-resistant cells and TRAIL-susceptible cells, with or without bortezomib, to compare their respective abilities to induce cell death. Recombinant TRAIL was treated with bortezomib to investigate whether this combination treatment could induce tumor regression in a mouse syngeneic tumor model. To understand the mechanism of combined treatment-induced cell death, cells were analyzed by flow cytometry and the effects of various cell death inhibitors on cell death rates were examined. RESULTS: ILz:rhTRAIL, a recombinant human TRAIL containing isoleucine zipper hexamerization domain, showed the highest cell death inducing ability both in single treatment and in combination treatment with bortezomib. In both TRAIL-resistant and TRAIL-susceptible cells treated with the combination treatment, an increase in cell death rates was dependent upon both the dose of TRAIL and its intrinsic properties. When a syngeneic mouse tumor model was treated with the combination of ILz:rhTRAIL and bortezomib, significant tumor regression was seen as a result of the effective induction of cancer cell death. The combination treatment-induced cell death was both inhibited by TRAIL blocking antibody and caspase-dependent. However, it was not inhibited by various ER stress inhibitors and autophagy inhibitors. CONCLUSIONS: The combination treatment with ILz:rhTRAIL and bortezomib was able to induce cell death in both TRAIL-susceptible and TRAIL-resistant cancer cells through the intracellular TRAIL signaling pathway. The efficiency of cell death was dependent on the properties of TRAIL under the environment provided by bortezomib. The combination treatment-induced cell death was not regulated by bortezomib-induced ER stress response or by autophagy.

Therapeutic Inhibitors against Mutated BRAF and MEK for the Treatment of Metastatic Melanoma.

Melanoma is one of the most aggressive cancers in the world and is responsible for the majority of skin cancer deaths. Recent advances in the field of immunotherapy using active, adoptive, and antigen-specific therapeutic approaches, have generated the expectation that these technologies have the potential to improve the treatment of advanced malignancies, including melanoma. Treatment options for metastatic melanoma patients have been dramatically improved by the FDA approval of new therapeutic agents including vemurafenib, dabrafenib, and sorafenib. These kinase inhibitors have the potential to work in tandem with MEK, PI3K/AKT, and mTOR to inhibit the activity of melanoma inducing BRAF mutations. This review summarizes the effects of the new therapeutic agents against melanoma and the underlying biology of these BRAF inhibitors.

Systematic Mutagenesis of Serine Hydroxymethyltransferase Reveals an Essential Role in Nematode Resistance.

Rhg4 is a major genetic locus that contributes to soybean cyst nematode (SCN) resistance in the Peking-type resistance of soybean (Glycine max), which also requires the rhg1 gene. By map-based cloning and functional genomic approaches, we previously showed that the Rhg4 gene encodes a predicted cytosolic serine hydroxymethyltransferase (GmSHMT08); however, the novel gain of function of GmSHMT08 in SCN resistance remains to be characterized. Using a forward genetic screen, we identified an allelic series of GmSHMT08 mutants that shed new light on the mechanistic aspects of GmSHMT08-mediated resistance. The new mutants provide compelling genetic evidence that Peking-type rhg1 resistance in cv Forrest is fully dependent on the GmSHMT08 gene and demonstrates that this resistance is mechanistically different from the PI 88788-type of resistance that only requires rhg1 We also demonstrated that rhg1-a from cv Forrest, although required, does not exert selection pressure on the nematode to shift from HG type 7, which further validates the bigenic nature of this resistance. Mapping of the identified mutations onto the SHMT structural model uncovered key residues for structural stability, ligand binding, enzyme activity, and protein interactions, suggesting that GmSHMT08 has additional functions aside from its main enzymatic role in SCN resistance. Lastly, we demonstrate the functionality of the GmSHMT08 SCN resistance gene in a transgenic soybean plant.

Impact of Grapevine (Vitis vinifera) Varieties on Reproduction of the Northern Root-Knot Nematode (Meloidogyne hapla).

One of the most commonly encountered plant-parasitic nematodes in eastern Washington Vitis vinifera vineyards is Meloidogyne hapla; however, limited research exists on the impact of this nematode on V. vinifera. The objectives of this research were to determine the impact of M. hapla on Chardonnay and Cabernet Sauvignon vine establishment and to determine the host status of V. vinifera varieties/clones predominantly grown in Washington to M. hapla. In a microplot experiment, Chardonnay and Cabernet Sauvignon vines were planted into soil inoculated with different densities of M. hapla; population dynamics of M. hapla and vine performance were monitored over 3 yr. In greenhouse experiments, several clones representing five V. vinifera varieties, Chardonnay, Riesling, Cabernet Sauvignon, Merlot, and Syrah, were evaluated as hosts for M. hapla. In both microplot and greenhouse experiments, white varieties were significantly better hosts than red varieties. In the greenhouse experiments, Chardonnay and Riesling had 40% higher reproduction factor values than Syrah and Merlot, however, all varieties/clones screened were good hosts for M. hapla (reproduction factors > 3). In the microplot experiment, M. hapla eggs/g root were 4.5 times greater in Chardonnay compared to Cabernet Sauvignon 3 yr after planting but there was no evident impact of M. hapla on vine establishment.

Spatial Distribution of Plant-Parasitic Nematodes in Semi-Arid Vitis vinifera Vineyards in Washington.

The most commonly encountered plant-parasitic nematodes in eastern Washington Vitis vinifera vineyards are Meloidogyne hapla, Mesocriconema xenoplax, Pratylenchus spp., Xiphinema americanum, and Paratylenchus sp.; however, little is known about their distribution in the soil profile. The vertical and horizontal spatial distribution of plant-parasitic nematodes was determined in two Washington V. vinifera vineyards. Others variables measured in these vineyards included soil moisture content, fine root biomass, and root colonization by arbuscular mycorhizal fungi (AMF). Meloidogyne hapla and M. xenoplax were aggregated under irrigation emitters within the vine row and decreased with soil depth. Conversely, Pratylenchus spp. populations were primarily concentrated in vineyard alleyways and decreased with depth. Paratylenchus sp. and X. americanum were randomly distributed within the vineyards. Soil water content played a dominant role in the distribution of fine roots and plant-parasitic nematodes. Colonization of fine roots by AMF decreased directly under irrigation emitters; in addition, galled roots had lower levels of AMF colonization compared with healthy roots. These findings will help facilitate sampling and management decisions for plant-parasitic nematodes in Washington semi-arid vineyards.