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Ribosome biogenesis is a fundamental and highly orchestrated process that involves hundreds of ribosome biogenesis factors. Despite advances that have been made in yeast, the molecular mechanism of ribosome biogenesis remains largely unknown in plants. We uncovered a WD40 protein, Shrunken and Embryo Defective Kernel 1 (SHREK1), and showed that it plays a crucial role in ribosome biogenesis and kernel development in maize (Zea mays). The shrek1 mutant shows an aborted embryo and underdeveloped endosperm and embryo-lethal in maize. SHREK1 localizes mainly to the nucleolus and accumulates to high levels in the seed. Depleting SHREK1 perturbs pre-rRNA processing and causes imbalanced profiles of mature rRNA and ribosome. The expression pattern of ribosomal-related genes is significantly altered in shrek1. Like its yeast (Saccharomyces cerevisiae) ortholog Periodic tryptophan protein 1 (PWP1), SHREK1 physically interacts with ribosomal protein ZmRPL7a, a transient component of the PWP1-subcomplex involved in pre-rRNA processing in yeast. Additionally, SHREK1 may assist in the A3 cleavage of the pre-rRNA in maize by interacting with the nucleolar protein ZmPOP4, a maize homolog of the yeast RNase mitochondrial RNA-processing complex subunit. Overall, our work demonstrates a vital role of SHREK1 in pre-60S ribosome maturation, and reveals that impaired ribosome function accounts for the embryo lethality in shrek1. [ABSTRACT FROM AUTHOR]

Objectives: Vancomycin-intermediate Staphylococcus aureus (VISA) strains have spread globally. We previously isolated an ST239 VISA (XN108) with a vancomycin MIC of 12 mg/L. The mechanism for XN108 resistance to vancomycin was investigated in this study.Methods: Genome comparison was performed to characterize mutations that might contribute to the XN108 resistance phenotype. The novel mutation WalK(S221P) was identified and investigated using allelic replacement experiments. Vancomycin susceptibilities, autolytic activities and morphologies of the strains were examined. Autophosphorylation activities of WalK and the WalK(S221P) mutant were determined in vitro with [λ- 32 P]ATP, and binding activity of WalK(S221P)-activated WalR to the promoter region of its target gene lytM was determined by electrophoretic mobility shift assay.Results: Genome comparison revealed three mutations, GraS(T136I), RpoB(H481N) and WalK(S221P), which might be responsible for vancomycin resistance in XN108. The introduction of WalK(S221P) to the vancomycin-susceptible strain N315 increased its vancomycin MIC from 1.5 to 8 mg/L, whereas the allelic replacement of WalK(S221P) with the native N315 WalK allele in XN108 decreased its vancomycin MIC from 12 to 4 mg/L. The VISA strains have thickened cell walls and decreased autolysis, consistent with observed changes in the expression of genes involved in cell wall metabolism and virulence regulation. WalK(S221P) exhibited reduced autophosphorylation, which may lead to reduced phosphorylation of WalR. WalK(S221P)-phosphorylated WalR also exhibited a reduced capacity to bind to the lytM promoter.Conclusions: The naturally occurring WalK(S221P) mutation plays a key role in vancomycin resistance in XN108. [ABSTRACT FROM AUTHOR]

Background: Artemisinin resistance in Plasmodium falciparum has emerged in Southeast Asia and poses a threat to malaria control and elimination. Mutations in a P. falciparum gene encoding a kelch protein on chromosome 13 have been associated with delayed parasite clearance following artemisinin treatment elsewhere in the region, but not yet in China.Methods: Therapeutic efficacy studies of artesunate and dihydroartemisinin-piperaquine were conducted from 2009 to 2012 in the Yunnan Province of China near the border with Myanmar. K13 mutations were genotyped by capillary sequencing of DNA extracted from dried blood spots collected in these clinical trials and in routine surveillance. Associations between K13 mutations and delayed parasite clearance were tested using regression models.Results: Parasite clearance half-lives were prolonged after artemisinin treatment, with 44% of infections having half-lives >5 hours (n = 109). Fourteen mutations in K13 were observed, with an overall prevalence of 47.7% (n = 329). A single mutation, F446I, predominated, with a prevalence of 36.5%. Infections with F446I were significantly associated with parasitemia on day 3 following artemisinin treatment and with longer clearance half-lives.Conclusions: Plasmodium falciparum infections in southern China displayed markedly delayed clearance following artemisinin treatment. F446I was the predominant K13 mutation and was associated with delayed parasite clearance. [ABSTRACT FROM AUTHOR]