Summary
Plant diseases inflict heavy losses on soybean yield, necessitating an understanding of the molecular mechanisms underlying biotic/abiotic stress responses. Ca2+ is an important universal ...messenger, and protein sensors, prominently calmodulins (CaMs), recognize cellular changes in Ca2+ in response to diverse signals. Because the development of stable transgenic soybeans is laborious and time consuming, we used the Bean pod mottle virus (BPMV)‐based vector for rapid and efficient protein expression and gene silencing. The present study focuses on the functional roles of the gene encoding the soybean CaM isoform GmCaM4. Overexpression of GmCaM4 in soybean resulted in enhanced resistance to three plant pathogens and increased tolerance to high salt conditions. To gain an understanding of the underlying mechanisms, we examined the potential defence pathways involved. Our studies revealed activation/increased expression levels of pathogenesis‐related (PR) genes in GmCaM4‐overexpressing plants and the accumulation of jasmonic acid (JA). Silencing of GmCaM4, however, markedly repressed the expression of PR genes. We confirmed the in vivo interaction between GmCaM4 and the CaM binding transcription factor Myb2, which regulates the expression of salt‐responsive genes, using the yeast two‐hybrid (Y2H) system and bimolecular fluorescence complementation assays. GmCaM4 and Glycine max CaM binding receptor‐like kinase (GmCBRLK) did not interact in the Y2H assays, but the interaction between GmCaM2 and GmCBRLK was confirmed. Thus, a GmCaM2–GmCBRLK‐mediated salt tolerance mechanism, similar to that reported in Glycine soja, may also be functional in soybean. Confocal microscopy showed subcellular localization of the green fluorescent protein (GFP)‐GmCaM4 fusion protein in the nucleus and cytoplasm.
The family
Totiviridae
includes a number of viruses with monosegmented dsRNA genomes and isometric virions that infect either fungi or a number of medically important protozoan parasites such as
...Leishmania
and
Giardia
. A new genus,
Trichomonasvirus
, was recently approved for this family. Its name is based on the genus of its host organism,
Trichomonas vaginalis
, a protozoan parasite that colonizes the human genitourinary mucosa and is the most common non-viral sexually transmitted infection in the world. The type species of this new genus is
Trichomonas vaginalis virus 1
. Distinguishing characteristics of the new genus include infection of a human sexually transmitted parasite, stable mixed infection with more than one distinct
Trichomonasvirus
species, and sequence-based phylogenetic divergence that distinguishes it from all other family members.
Stearoyl-acyl carrier protein-desaturase (SACPD)-catalyzed synthesis of oleic acid (18:1) is an essential step in fatty acid biosynthesis. Arabidopsis mutants (ssi2) with reduced SACPD activity ...accumulate salicylic acid (SA) and exhibit enhanced resistance to multiple pathogens. We show that reduced levels of 18:1 induce similar defense-related phenotypes in soybean. A Bean pod mottle virus (BPMV)-based vector was employed to effectively silence soybean SACPDs. The silenced plants contained reduced 18:1 and increased stearic acid, developed spontaneous cell death lesions, increased SA accumulation, and constitutively expressed pathogenesis-related genes. These plants also expressed elevated levels of resistance-like genes and showed resistance to bacterial and oomycete pathogens. Exogenous application of glycerol induced similar phenotypes, mimicking the effect of silencing SACPDs in healthy soybean plants. Overexpression of a soybean SACPD increased 18:1 levels in ssi2 but not in wild-type Arabidopsis plants, suggesting that the soybean enzyme was under feedback regulation similar to that of the Arabidopsis isozymes. These results suggest that soybean and Arabidopsis respond similarly to 18:1-derived cues by inducing a novel broad-spectrum resistance-conferring pathway, even though they differ significantly in their lipid biosynthetic pathways. We also demonstrate the efficacy of BPMV-induced gene silencing as a tool for functional studies in soybean.
My long career in virology has been a continuous learning exercise with a very modest start. Virology and related pertinent fields have changed significantly during my lifetime. Sometimes I wish that ...my career had just started and I could apply all available and state of the art technology to solving problems and explaining intriguing observations. I was always convinced that visiting growers' fields is essential for researchers to get firsthand observations and knowledge of virus disease problems under field conditions. I never thought I would pursue so many avenues of research, yet it is true that research never ends. I enjoyed dissecting strain diversity in a very important plant pathogen like bean pod mottle virus (BPMV) and using BPMV-based vectors to address fundamental virology questions. Lastly, solving the enigma of the transmissible disease of
Helminthosporium victoriae
and attempting to gain an understanding of the molecular basis of disease in a plant pathogenic fungus were thrilling.
•Conclusive evidence that HvV190S is the primary causal agent of a transmissible disease of its natural host Helminthosporium victoriae.•Infection with HvV190S alone does not induce over-expression ...of the cellular multifunctional protein Hv-p68.•The host range of HvV190S is extended to include Cryphonectria parasitica strain Δdcl-2.•HvV190S-infected C. parasitica strain Δdcl-2 exhibits disease symptoms similar to those of virus-infected H. victoriae.•HvV190S infection induces anti-fungal activity in its new C. parasitica host.
A transmissible disease of the plant pathogenic fungus Helminthosporium victoriae, the causal agent of Victoria blight of oats, was reported more than 50 years ago. Diseased, but not normal, isolates, of H. victoriae contain two distinct viruses designated according to their sedimentation values as victorivirus Helminthosporium victoriae virus 190S (HvV190S) and chrysovirus Helminthosporium victoriae 145S (HvV145S). Although a viral etiology of the disease was previously proposed, conclusive evidence was lacking. Here we present unequivocal evidence based on transfecting virus-free H. victoriae protoplasts with purified virus particles showing that HvV190S is essential for disease development. Furthermore, we show an expansion of the host range of HvV190S to include Cryphonectria parasitica and we also show similarity in a subset of phenotypic traits between HvV190S-infected RNA silencing deficient mutant (Δdcl-2) of C. parasitica and a strain of H. victoriae. In virulence assays on detached American chestnut branches and Red Delicious apple fruits, HvV190S-infected C. parasitica strain Δdcl-2 was markedly less virulent than wild type and virus-free Δdcl-2 C. parasitica strains. Furthermore, the hypovirulent HvV190S-infected C. parasitica Δdcl-2 strain exhibited strong antifungal activity in dual culture with the plant pathogenic fungus Sclerotinia sclerotiorum. No such inhibitory activity was observed in comparable dual cultures with wild type and virus-free Δdcl-2 C. parasitica strains. The discovery that infection with HvV190S induced a hypovirulent phenotype in a heterologous plant pathogenic host is very significant since it might be possible to convert other economically important plant pathogenic fungi to hypovirulence using HvV190S.
Viruses evolve so rapidly that sequence-based comparison is not suitable for detecting relatedness among distant viruses. Structure-based comparisons suggest that evolution led to a small number of ...viral classes or lineages that can be grouped by capsid protein (CP) folds. Here, we report that the CP structure of the fungal dsRNA Penicillium chrysogenum virus (PcV) shows the progenitor fold of the dsRNA virus lineage and suggests a relationship between lineages. Cryo-EM structure at near-atomic resolution showed that the 982-aa PcV CP is formed by a repeated α-helical core, indicative of gene duplication despite lack of sequence similarity between the two halves. Superimposition of secondary structure elements identified a single “hotspot” at which variation is introduced by insertion of peptide segments. Structural comparison of PcV and other distantly related dsRNA viruses detected preferential insertion sites at which the complexity of the conserved α-helical core, made up of ancestral structural motifs that have acted as a skeleton, might have increased, leading to evolution of the highly varied current structures. Analyses of structural motifs only apparent after systematic structural comparisons indicated that the hallmark fold preserved in the dsRNA virus lineage shares a long (spinal) α-helix tangential to the capsid surface with the head-tailed phage and herpesvirus viral lineage.
PDF
