We isolated the kexB gene, which encodes a subtilisin-like processing enzyme, from a filamentous fungus, Aspergillus oryzae. To examine the physiological role of kexB in A. oryzae, we constructed a kexB disruptant (⌬kexB), which formed shrunken colonies with poor generation of conidia on Czapek-Dox (CD) agar plates and hyperbranched mycelia in CD liquid medium. The phenotypes of the ⌬kexB strain were restored under high osmolarity in both solid and liquid culture conditions. We found that transcription of the mpkA gene, which encodes a putative mitogen-activated protein kinase involved in cell integrity signaling, was significantly higher in ⌬kexB cells than in wild-type cells. The ⌬kexB cells also contained higher levels of transcripts for cell wallrelated genes encoding ␤-1,3-glucanosyltransferase and chitin synthases, which is presumably attributable to cell integrity signaling through the increased gene expression of mpkA. As expected, constitutively increased levels of phosphorylated MpkA were observed in ⌬kexB cells on the CD plate culture. High osmotic stress greatly downregulated the increased levels of both transcripts of mpkA and the phosphorylated form of MpkA in ⌬kexB cells, concomitantly suppressing the morphological defects. These results suggest that the upregulation of transcription levels of mpkA and cell wall biogenesis genes in the ⌬kexB strain is autoregulated by phosphorylated MpkA as the active form through cell integrity signaling. We think that KexB is required for precise proteolytic processing of sensor proteins in the cell integrity pathway or of cell wall-related enzymes under transcriptional control by the pathway and that the KexB defect thus induces disordered cell integrity signaling.

No abstract

No abstract

de transition (Q.L.L.) h la surface dlun cristal de glace h tdrature juste en-dessous du point de fusion (O°C) ont 6th mesurds h 116quilibre en utilisant une m6thode d'ellipscnn6trie in-situ. Les couches de transition ont dtd-observ6es h des tdratures sdrieures h -2 et -4OC pour les faces f 0001fet ~1 0 1 0~ respectivement et n1 = 1,330 pour les deux faces. Cette valeur est tres proche de celle de l'eau en volume h 0°C. ~ssoci6 h des observations sur les formes des cristaux de glace prbs du point de fusion, on doit s1attendre h ce que 13 structure de llinterface entre la couche de transition et la glace sur la face {lolo! varie brutalement au-dessous de -Z°C pour devenir plus rugueuse.Abstract : The refractive index nl and the thickness d of the transition layer ( q u a s i -l i q u i d layer) on the surface of an ice crystal a t temperatures just below the me1 ting point (0°C) were measured in equilibrium, using an in-situ method of el lipsometry.The transition layers were observed a t temperatures above -2 and -4°C for (0001)-and {1010}-faces, respectively, and n was 1.330 f o r both faces, which i s very close t o the refractive index of bulk w a k r a t O°C (nw=1.333). Combined with the observational results about the ice crystal shapes near the melting point, i t was expected that the interface structure between transition layer and ice on the (1010)-face changes from smooth t o rough a t -2°C.

No abstract