Welcoming PhytoFrontiers™ into Our APS Family of Journals

The American Phytopathological Society (APS) is launching the new journal PhytoFrontiers™. As with many other gold open access (OA) journals, manuscripts will not be judged on novelty but rather solely on quality and scientific rigor. The expectation therefore is that the manuscripts are based on solid experimental design, robust statistical analyses, and quality technical writing. PhytoFrontiers explicitly encourages publication of negative results because it removes a significant and persistent bias from the literature. PhytoFrontiers establishes a new venue for our plant health colleagues in Europe and elsewhere who are required by their institutions or funders to publish in gold OA journals (i.e., journals that allow immediate access to all content). PhytoFrontiers complements our established journals by providing a new place for manuscripts that do not fit the subject areas currently covered in our five existing journals. These papers might cover subjects as broad as robotics, microbial taxonomy, and those that focus primarily on abiotic stress responses, in addition to all of those plant health subjects typically found in our other APS journals, and potentially other subject areas. We are excited to launch this new journal and hope you will consider PhytoFrontiers for your next submission. Follow us on our new journey on Twitter @PhytoFrontiers.[Graphic: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 202

A comparison of the effects of DNA-damaging agents and biotic elicitors on the induction of plant defense genes, nuclear distortion, and cell death

Pea (Pisum sativum L. cv Alcan) endocarp tissue challenged with an incompatible fungal pathogen, Fusarium solani f. sp. phaseoli or fungal elicitors results in the induction of pathogenesis-related (PR) genes and the accumulation of pisatin, a phytoalexin. Essentially the same response occurs in pea tissue exposed to DNA-specific agents that crosslink or intercalate DNA. In this study, the effects of DNA-damaging agents were assessed relative to the inducible expression of several pea PR genes: phenylalanine ammonia lyase, chalcone synthase, and DRR206. Mitomycin C and actinomycin D mimicked the biotic elicitors in enhancing the expression of all three PR genes. The activities of these PR gene promoters, isolated from different plants, were evaluated heterologously in transgenic tobacco. It is remarkable that β-glucuronidase expression was induced when plants containing the heterologous phenylalanine ammonia lyase, chalcone synthase, and DRR206 promoter-β-glucuronidase chimeric reporter genes were treated by DNA-damaging agents. Finally, cytological analyses indicated that many of these agents caused nuclear distortion and collapse of the treated pea cells. Yet we observed that cell death is not necessary for the induction of the PR gene promoters assessed in this study. Based on these observations and previously published results, we propose that DNA damage or the associated alteration of chromatin can signal the transcriptional activation of plant defense genes

RNA-seq analyses of gene expression in the microsclerotia of Verticillium dahliae

Abstract Background The soilborne fungus, Verticillium dahliae, causes Verticillium wilt disease in plants. Verticillium wilt is difficult to control since V. dahliae is capable of persisting in the soil for 10 to 15 years as melanized microsclerotia, rendering crop rotation strategies for disease control ineffective. Microsclerotia of V. dahliae overwinter and germinate to produce infectious hyphae that give rise to primary infections. Consequently, microsclerotia formation, maintenance, and germination are critically important processes in the disease cycle of V. dahliae. Results To shed additional light on the molecular processes that contribute to microsclerotia biogenesis and melanin synthesis in V. dahliae, three replicate RNA-seq libraries were prepared from 10 day-old microsclerotia (MS)-producing cultures of V. dahliae, strain VdLs.17 (average = 52.23 million reads), and those not producing microsclerotia (NoMS, average = 50.58 million reads). Analyses of these libraries for differential gene expression revealed over 200 differentially expressed genes, including up-regulation of melanogenesis-associated genes tetrahydroxynaphthalene reductase (344-fold increase) and scytalone dehydratase (231-fold increase), and additional genes located in a 48.8 kilobase melanin biosynthetic gene cluster of strain VdLs.17. Nearly 50% of the genes identified as differentially expressed in the MS library encode hypothetical proteins. Additional comparative analyses of gene expression in V. dahliae, under growth conditions that promote or preclude microsclerotial development, were conducted using a microarray approach with RNA derived from V. dahliae strain Dvd-T5, and from the amicrosclerotial vdh1 strain. Differential expression of selected genes observed by RNA-seq or microarray analysis was confirmed using RT-qPCR or Northern hybridizations. Conclusion Collectively, the data acquired from these investigations provide additional insight into gene expression and molecular processes that occur during MS biogenesis and maturation in V. dahliae. The identified gene products could therefore potentially represent new targets for disease control through prevention of survival structure development.The authors acknowledge funding from the California Department of Food and Agriculture, Agreement SCB09023, and Natural Sciences and Engineering Research Council of Canada. We are thankful for the help of Patrick Chapman for contributions in tabulating microarray data for database submission.Peer Reviewe

Hormone Signaling and Its Interplay With Development and Defense Responses in Verticillium-Plant Interactions.

Soilborne plant pathogenic species in the fungal genus Verticillium cause destructive Verticillium wilt disease on economically important crops worldwide. Since R gene-mediated resistance is only effective against race 1 of V. dahliae, fortification of plant basal resistance along with cultural practices are essential to combat Verticillium wilts. Plant hormones involved in cell signaling impact defense responses and development, an understanding of which may provide useful solutions incorporating aspects of basal defense. In this review, we examine the current knowledge of the interplay between plant hormones, salicylic acid, jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid, auxin, and nitric oxide, and the defense responses and signaling pathways that contribute to resistance and susceptibility in Verticillium-host interactions. Though we make connections where possible to non-model systems, the emphasis is placed on Arabidopsis-V. dahliae and V. longisporum interactions since much of the research on this interplay is focused on these systems. An understanding of hormone signaling in Verticillium-host interactions will help to determine the molecular basis of Verticillium wilt progression in the host and potentially provide insight on alternative approaches for disease management

Morphogenesis and virulence are regulated by overlapped but distinct molecular mecanisms in Verticillium dahliae

Póster presentado en el XVIII Congreso de la Sociedad Española de Fitopatología (SEF), celebrado en Palencia del 20 al 23 de septiembre de 2016.The soildborne pathogen Verticillium dahliae poses a threat to many important crops worldwide. V. dahliae produces highly durable structures, the microsclerotia, which germinate in the presence of root exudates from the host, producing hyphae that penetrate the root cortex. Upon reaching the xylem, a combination of sporulation and filamentous growth is thought to contribute to vascular colonization. A number of genes have been identified whose alteration affects both virulence and microsclerotium development. This led to postulate that these processes are inextricably linked and coregulated. Two major signalling pathways, MAPK cascades and cAMP signalling, have been implicated in the regulation of morphogenesis and virulence in fungi. In this work, we functionally characterized three regulatory proteins which are potential downstream targets of these regulatory pathways, revealing that microsclerotium development and virulence can be fully uncoupled. Thus, deletion of the APSES transcription factor (TF) gene vst1 abolished microsclerotium production and altered sporulation processes but did not diminish the ability of the fungus to colonize the host. By contrast, deletion of vph1, a putative homolog of the major target of MAPK signalling ste12, did not affect vegetative growth but rendered strains avirulent. Deletion of vhb1, encoding a protein similar to homeobox TFs involved in sporulation, greatly impacted sporulation but not microsclerotium development and also rendered strains avirulent. Confocal microscopy showed that Δvph1 could not penetrate the root cortex while Δvhb1 was impaired in its ability to proliferate in the xylem. Interestingly, a microarray analysis identified an important overlap in the genes under Vst1 and Vph1 regulation. We propose that different downstream targets allow the fungus to regulate particular aspects of morphogenesis and virulence through the same pathways. The specific role and putative connection with other components of the signalling pathways of each TF characterized will be discussed.N

Diversity, Pathogenicity, and Management of Verticillium Species

The genus Verticillium encompasses phytopathogenic species that cause vascular wilts of plants. In this review, we focus on Verticillium dahliae, placing emphasis on the controversy surrounding the elevation of a long-spored variant as a new species, recent advances in the analysis of compatible and incompatible interactions, highlighted by the use of strains expressing fluorescent proteins, and the genetic diversity among Verticillium spp. A synthesis of the approaches to explore genetic diversity, gene flow, and the potential for cryptic recombination is provided. Control of Verticillium wilt has relied on a panoply of chemical and nonchemical strategies, but is beset with environmental or site-specific efficacy problems. Host resistance remains the most logical choice, but is unavailable in most crops. The genetic basis of resistance to Verticillium wilt is unknown in most crops, as are the subcellular signaling mechanisms associated with Ve-mediated, race-specific resistance. Increased understanding in each of these areas promises to facilitate management of Verticillium wilts across a broad range of crops

The Transcription Factor VdHapX Controls Iron Homeostasis and Is Crucial for Virulence in the Vascular Pathogen Verticillium dahliae

This study demonstrated that VdHapX is a conserved protein that mediates adaptation to iron starvation and excesses, affects microsclerotium formation, and is crucial for virulence of V. dahliae.Iron homeostasis is essential for full virulence and viability in many pathogenic fungi. Here, we showed that the bZip transcription factor VdHapX functions as a key regulator of iron homeostasis for adaptation to iron-depleted and iron-excess conditions and is required for full virulence in the vascular wilt fungus, Verticillium dahliae. Deletion of VdHapX impaired mycelial growth and conidiation under both iron starvation and iron sufficiency. Furthermore, disruption of VdHapX led to decreased formation of the long-lived survival structures of V. dahliae, known as microsclerotia. Expression of genes involved in iron utilization pathways and siderophore biosynthesis was misregulated in the ΔVdHapX strain under the iron-depleted condition. Additionally, the ΔVdHapX strain exhibited increased sensitivity to high iron concentrations and H2O2, indicating that VdHapX also contributes to iron or H2O2 detoxification. The ΔVdHapX strain showed a strong reduction in virulence on smoke tree seedlings (Cotinus coggygria) and was delayed in its ability to penetrate plant epidermal tissue

Crustacean Meal Elicits Expression of Growth and Defense-Related Genes in Roots of Lettuce and Tomato

Powdered crab and lobster shells (crustacean meal) obtained from fisheries are used as soil amendments to promote plant health and defense. In this study, a commercial crustacean meal amendment used to promote the health of lettuce, tomato, and other crop plants was applied to roots of lettuce and tomato seedlings. Gene expression profiling of the treated roots was assessed by RNA sequencing (RNA-seq) at 24 h after application relative to a 0 h time point. The RNA-seq analyses revealed upregulation of different types of genes in both tomato and lettuce roots at 24 h. Gene ontology analyses revealed increased expression of genes associated with oxidoreductases/metal ion binding in tomato roots at 24 h, while there was predominantly increased expression of genes associated with cell wall organization, lyases, and hydrolases in lettuce roots at 24 h. The types of defense-related genes expressed were also markedly different. In tomato roots, the most highly induced gene (log2 fold change 13.84, P ≤ 0.001) encoded a defense-associated miraculin-like protein, but transcripts of a similar gene were not induced in lettuce roots. Interestingly, phenylpropanoid pathway genes relating to cell wall biogenesis and lignification were significantly upregulated in both lettuce and tomato roots, suggesting that strengthening of plant cell walls is a common response to crustacean meal application. This research provides insight into gene expression patterns in the roots of lettuce and tomato in response to crustacean meal, improving our understanding of how this amendment could aid in plant health. [Graphic: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022