Functional and transcriptomic analyses in Neurospora crassa reveal a crucial role for the N-glycoprotein deglycosylation process in fungal homeostasis.

The Conserved N-Terminal Extension of AtKEA1 Is Largely Dispensable for Plastid Function but Contributes to Potassium Homeostasis

An evolutionarily ancient regulatory module is uncovered that shapes the molecular organization and function of IE KEAs, advancing the understanding of plastid ion and pH homeostasis and plastid ribosome integrity.

Identification of cellular intermediates unveils unique enzymes for flagellar glycan biosynthesis in Clostridioides difficile.

Glycosylation of bacterial surface proteins, such as flagellin (FliC), is important for their function and is often involved in virulence of pathogens. Glycans can be further modified by so-called postglycosylation modifications (PGMs), often resulting in exclusive molecular structures. In Clostridioides difficile, a unique glycan structure (Type A) decorates FliC (which forms the flagellar filament) that consists of an O-linked N-acetyl-β-d-glucosamine (GlcNAc) modified with an N-methyl-L-threonine via a phosphodiester linkage. This PGM is synthesized by a set of four enzymes encoded in one operon (ftaABCD), but the exact biosynthesis pathway and biosynthetic intermediates remain unknown. In this study, we chemically synthesized two hitherto undescribed biosynthetic intermediates that we predicted based on bioinformatic analyses, CDP-threonine and CDP-N-methylthreonine. We showed that they are involved in the Type A PGM biosynthesis, as evidenced by mass spectrometric analyses of extracts of a set of C. difficile mutant strains. Furthermore, we characterized FtaC to be a SAM-dependent CDP-threonine N-methyltransferase that installs the methyl group on CDP-threonine prior to transfer of the PGM to GlcNAc-FliC, and we revealed FtaD as the CDP-N-methylthreonine:GlcNAc N-methylthreoninephosphotransferase. Finally, using recombinantly expressed FtaC and FtaD in combination with synthetic CDP-threonine, we reconstituted the biosynthesis pathway of the Type A PGM in vitro. Overall, our results open avenues to explore these unique biosynthesis enzymes in molecular detail to provide new points of entry for the development of biosynthesis inhibitors and tools to study the role of this PGM in virulence and flagellar function.

Functional diversification of UBP6 in plant immunity through N-degron pathway regulation

An extended N-terminus restrains the plant cell death-inducing ability of the catalytically competent ribonuclease domain in a pea powdery mildew RALPH effector

A previously unrecognized mechanism regulating RNase activity in a dicot PM RALPH effector is revealed and new insights are provided into the functional diversification of RALPHs and their adaptation to obligate biotrophy.

The Slt2-Swi6 signaling pathway plays a pivotal role in regulating cell wall biosynthesis, secondary metabolite production, and the pathogenicity of pear fungal A. alternata

A physical interaction is identified between AaSlt2 and Swi6/RlmA, suggesting that these components are critical for cell wall synthesis, which advances the understanding of pathogenic mechanisms of A. alternata and proposes potential strategies for controlling postharvest diseases.

The mitoribosome-associated factor Mrx9 acts as a negative regulator of the prohibitin/m-AAA complex

The synthesis of mitochondrial-encoded polypeptides is an essential process, primarily regulated at the posttranscriptional level. In yeast, many regulatory factors have been described as acting in proximity to the mitoribosome to promote efficient translation; however, the precise mechanisms by which these components function remain largely unknown. Here, we expand on findings concerning a previously studied mitoribosome interactor, Mrx9, which is found in large expressosome-like assemblies of mitoribosome clusters. Mrx9 was initially linked to mitochondrial translation and was suggested to be associated with the splicing of COX1 and COB transcripts. Our current data show that Mrx9 is associated with the PHB/m-AAA complex at the polypeptide exit tunnel of the mitoribosome. Overexpression of Mrx9 impairs the proteolytic functions of Yta10 and Yta12 within the prohibitin complex, leading to splicing defects; accumulation of aberrant polypeptides; and a noticeable impairment in the processing of the essential mitoribosomal protein bL32m. These findings support a regulatory role for Mrx9 in the PHB/m-AAA complex by modulating the activities of both Yta10 and Yta12.