Intramembrane protease RHBDL4 cleaves oligosaccharyltransferase subunits to target them for ER-associated degradation.

The endoplasmic reticulum (ER)-resident intramembrane rhomboid protease RHBDL4 generates metastable protein fragments and together with the ER-associated degradation (ERAD) machinery provides a clearance mechanism for aberrant and surplus proteins. However, the endogenous substrate spectrum and with that the role of RHBDL4 in physiological ERAD is mainly unknown. Here, we use a substrate trapping approach in combination with quantitative proteomics to identify physiological RHBDL4 substrates. This revealed oligosaccharyltransferase (OST) complex subunits such as the catalytic active subunit STT3A as substrates for the RHBDL4-dependent ERAD pathway. RHBDL4-catalysed cleavage inactivates OST subunits by triggering dislocation into the cytoplasm and subsequent proteasomal degradation. RHBDL4 thereby controls the abundance and activity of OST, suggesting a novel link between the ERAD machinery and glycosylation tuning.

Marker-free genome editing in Ustilago trichophora with the CRISPR-Cas9 technology.

In this communication, we report the adaptation of the CRISPR-Cas9 technology in Ustilago trichophora prototrophic wild-type isolate obtained from its natural host Echinochloa crus-galli. The established CRISPR vector and method enable a rapid and marker-free introduction of Cas9-induced non-homologous end-joining (NHEJ) dependent mutation at the targeted gene. Moreover, the method allows a specific modification of the chromosomal DNA sequence by Cas9-induced homologous recombination using short DNA repair templates. The results demonstrate the applicability of the CRISPR-Cas9 technology in U. trichophora for both gene knock-out by the NHEJ pathway and specific gene modification by templated genome editing, paving the way for rapid metabolic engineering of this Ustilago species for industrial applications.