Abstract
Transcriptional regulation is critical for plant pathogen development and virulence. MADS-box transcription factors belong to a highly conserved transcriptional regulator family in eukaryotic organisms that are involved in various important biological processes. Only one predicted MADS-box gene, PsMAD1, was identified in Phytophthora sojae, which was highly expressed during the sporangia and infection stages. To investigate its function, we generated PsMAD1 knockout mutants using the CRISPR/Cas9 system. Compared with the wild-type strain, the mutants showed no changes in vegetative growth, oospore production, or no differences in sensitivity to various abiotic stresses. Although sporangia production was normal, no zoospore release was detected in PsMAD1 mutants. Microscopy analyses revealed failure of cleavage of the cytoplasm into uninucleate zoospores in the mutants. In addition, the mutants showed reduced virulence in soybean. RNA-seq data indicated that PsMAD1 may regulate many zoospore development and infection associated genes. Thus, PsMAD1 may be a major regulator of P. sojae involved in zoosporogenesis and pathogenesis.
Highlights
Oomycetes are fungus-like eukaryotic microorganisms belonging to the stramenopile kingdom
We identified a MADS-box Transcription factors (TFs) candidate gene (Ps143579, named PsMAD1) that was highly expressed during the sporangia and infection stages, and confirmed the expression pattern with quantitative reverse transcriptionPCR (Figure 1A)
A phylogenetic tree constructed using full-length protein sequences of PsMAD1 and the homologs from oomycetes and fungi showed that the oomycete MADS-box TF proteins were conserved and the clade of them were close to that of RLM1, they likely belong to the myocyte enhancer factor 2 (MEF2)-type family (Supplementary Figure S1)
Summary
Oomycetes are fungus-like eukaryotic microorganisms belonging to the stramenopile kingdom. They are evolutionarily closely related to photosynthetic algae such as brown algae and diatoms but are distant from fungi. Soybean (Glycine max L.) root and stem rot caused by Phytophthora sojae is one of the most destructive diseases in soybean production, with an annual cost of $1–2 billion worldwide (Tyler, 2007). The main vectors of P. sojae dispersal are oospores and zoospores. Oospores have a thickwalled survival structure for sexual reproduction, which is responsible for their survival in extreme environments and ability to trigger new epidemics in subsequent growing seasons (Judelson and Blanco, 2005). Zoospores are an asexual reproduction structure and the most important route of
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