Disruption of ppr3, ppr4, ppr6 or ppr10 induces flocculation and filamentous growth in Schizosaccharomyces pombe

The deletion of ppr2 interferes iron sensing and leads to oxidative stress response in Schizosaccharomyces pombe

Pentatricopeptide repeat proteins are involved in mitochondrial both transcriptional and posttranscriptional regulation. Schizosaccharomyces pombe Ppr2 is a general mitochondrial translation factor that plays a critical role in the synthesis of all mitochondrial DNA-encoded oxidative phosphorylation subunits, which are essential for mitochondrial respiration. Our previous analysis showed that ppr2 deletion resulted in increased expression of iron uptake genes and caused ferroptosis-like cell death in S. pombe. In the present work, we showed that deletion of ppr2 reduced viability on glycerol- and galactose-containing media.Php4 is a transcription repressor that regulates iron homeostasis in fission yeast. We found that in the ppr2 deletion strain, Php4 was constitutively active and accumulated in the nucleus in the stationary phase. We also found that deletion of ppr2 decreased the ferroptosis-related protein Gpx1 in the mitochondria. Overexpression of Gpx1 improves the viability of Δppr2 cells. We showed that the deletion of ppr2 increased the production of ROS, downregulated heme synthesis and iron-sulfur cluster proteins, and induced stress proteins. Finally, we observed the nuclear accumulation of Pap1-GFP and Sty1-GFP, suggesting that Sty1 and Pap1 in response to cellular stress in the ppr2 deletion strain. These results suggest thatppr2 deletion may cause mitochondrial dysfunction, which is likely to lead to iron-sensing defect and iron starvation response, resulting in perturbation of iron homeostasis and increased hydroxyl radical production. The increased hydroxyl radical production triggers cellular responses in theppr2 deletion strain.

LAMMER Kinase Governs the Expression and Cellular Localization of Gas2, a Key Regulator of Flocculation in Schizosaccharomyces pombe

It was reported that LAMMER kinase in Schizosaccharomyces pombe plays an important role in cation-dependent and galactose-specific flocculation. Analogous to other flocculating yeasts, when cell wall extracts of the Δlkh1 strain were treated to the wild-type strain, it displayed flocculation. Gas2, a 1,3-β-glucanosyl transferase, was isolated from the EDTA-extracted cell-surface proteins in the Δlkh1 strain. While disruption of the gas2+ gene was not lethal and reduced the flocculation activity of the ∆lkh1 strain, the expression of a secreted form of Gas2, in which the GPI anchor addition sequences had been removed, conferred the ability to flocculate upon the WT strain. The Gas2-mediated flocculation was strongly inhibited by galactose but not by glucose. Immunostaining analysis showed that the cell surface localization of Gas2 was crucial for the flocculation of fission yeast. In addition, we identified the regulation of mbx2+ expression by Lkh1 using RT-qPCR. Taken together, we found that Lkh1 induces asexual flocculation by regulating not only the localization of Gas2 but also the transcription of gas2+ through Mbx2.

The FpPPR1 Gene Encodes a Pentatricopeptide Repeat Protein That Is Essential for Asexual Development, Sporulation, and Pathogenesis in Fusarium pseudograminearum

Fusarium crown rot (FCR) and Fusarium head blight (FHB) are caused by Fusarium pseudograminearum and are newly emerging diseases of wheat in China. In this study, we characterized FpPPR1, a gene that encodes a protein with 12 pentatricopeptide repeat (PPR) motifs. The radial growth rate of the ΔFpppr1 deletion mutant was significantly slower than the wild type strain WZ-8A on potato dextrose agar plates and exhibited significantly smaller colonies with sector mutations. The aerial mycelium of the mutant was almost absent in culture tubes. The ΔFpppr1 mutant was able to produce spores, but spores of abnormal size and altered conidium septum shape were produced with a significant reduction in sporulation compared to wild type. ΔFpppr1 failed to cause disease on wheat coleoptiles and barley leaves using mycelia plugs or spore suspensions. The mutant phenotypes were successfully restored to the wild type levels in complemented strains. FpPpr1-GFP signals in spores and mycelia predominantly overlapped with Mito-tracker signals, which substantiated the mitochondria targeting signal prediction of FpPpr1. RNAseq revealed significant transcriptional changes in the ΔFpppr1 mutant with 1,367 genes down-regulated and 1,333 genes up-regulated. NAD-binding proteins, thioredoxin, 2Fe-2S iron-sulfur cluster binding domain proteins, and cytochrome P450 genes were significantly down-regulated in ΔFpppr1, implying the dysfunction of mitochondria-mediated reductase redox stress in the mutant. The mating type idiomorphic alleles MAT1-1-1, MAT1-1-2, and MAT1-1-3 in F. pseudograminearum were also down-regulated after deletion of FpPPR1 and validated by real-time quantitative PCR. Additionally, 21 genes encoding putative heterokaryon incompatibility proteins were down-regulated. The yellow pigmentation of the mutant was correlated with reduced expression of PKS12 cluster genes. Taken together, our findings on FpPpr1 indicate that this PPR protein has multiple functions in fungal asexual development, regulation of heterokaryon formation, mating-type, and pathogenesis in F. pseudograminearum.