Abstract
The mevalonate (MVA) pathway in eukaryotic organisms produces isoprenoids, sterols, ubiquinone, and dolichols. These molecules are vital for diverse cellular functions, ranging from signaling to membrane integrity, and from post-translational modification to energy homeostasis. However, information on the MVA pathway in Phytophthora species is limited. In this study, we identified the MVA pathway genes and reconstructed the complete pathway in Phytophthora sojae in silico. We characterized the function of the MVA pathway of P. sojae by treatment with enzyme inhibitor lovastatin, deletion of the geranylgeranyl diphosphate synthase gene (PsBTS1), and transcriptome profiling analysis. The MVA pathway is ubiquitously conserved in Phytophthora species. Under lovastatin treatment, mycelial growth, spore production, and virulence of P. sojae were inhibited but the zoospore encystment rate increased. Heterozygous mutants of PsBTS1 showed slow growth, abnormal colony characteristics, and mycelial morphology. Mutants showed decreased numbers of sporangia and oospores as well as reduced virulence. RNA sequencing analysis identified the essential genes in sporangia formation were influenced by the enzyme inhibitor lovastatin. Our findings elucidate the role of the MVA pathway in P. sojae and provide new insights into the molecular mechanisms underlying the development, reproduction, and virulence of P. sojae and possibly other oomycetes. Our results also provide potential chemical targets for management of plant Phytophthora diseases.
Highlights
Oomycetes are a diverse group of fungus-like eukaryotic microorganisms that are phylogenetically distinct from fungi and classified within the stramenopila kingdom
In P. sojae, we observed that the growth rate decreased with increasing concentrations of lovastatin (Figures 2A,D) and the highest concentration that was tested, i.e., 80 μg/ml, mycelial growth was reduced with 31.9%
Similar inhibitory effects of lovastatin were observed in P. infestans, P. capsici, and Py. ultimum (Supplementary Figure S1)
Summary
Oomycetes are a diverse group of fungus-like eukaryotic microorganisms that are phylogenetically distinct from fungi and classified within the stramenopila kingdom. There are more than 100 species of oomycetes that cause destructive diseases in agriculture, and they are considered the most destructive species of plant pathogens (Kroon et al, 2012; Kamoun et al, 2015). Phytophthora infestans is a notorious oomycete pathogen that causes late blight in potato and tomato worldwide (Fry, 2008). Phytophthora sojae is another notorious species that causes root and stem rot disease in soybean, resulting in approximately $2 billion losses worldwide annually (Tyler, 2007). The extraordinary genetic plasticity of Phytophthora enables the pathogens to adapt rapidly to, and overcome, chemical or host resistance, which makes controlling the diseases more difficult (Fawke et al, 2015)
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