ABSTRACT
Tissue alkalinization during Colletotrichum gloeosporioides attack enhances the expression of PELB, which encodes pectate lyase (PL), and PL secretion, which is considered essential for full virulence. We studied the regulation of PL secretion by manipulation of C. gloeosporioides PELB. PELB was down-regulated by knocking out PAC1, which encodes the PacC transcription factor that regulates gene products with pH-sensitive activities. We functionally characterized a PACC gene homologue, PAC1, from C. gloeosporioides wild-type (WT) Cg-14 and two independent deletion strains, Deltapac1(372)and Deltapac1(761). Loss-of-function PAC1 mutants showed 85% reduction of PELB transcript expression, delayed PL secretion and dramatically reduced virulence, as detected in infection assays with avocado fruits. In contrast, PELB was up-regulated in the presence of carbon sources such as glucose. When glucose was used as a carbon source in the medium for the WT strain and the Deltapac1 mutant at pH 6.0, PELB transcript expression and PL secretion were activated. Other sugars, such as sucrose and fructose (but not galactose), also activated PELB expression. These results suggest that the pH-regulated response is only part of a multi-factor regulation of PELB, and that sugars are also needed to promote the transition from quiescent to active necrotrophic development by the pathogen.
Subject(s)
Colletotrichum/metabolism , Fruit/microbiology , Fungal Proteins/metabolism , Persea/microbiology , Polysaccharide-Lyases/metabolism , Colletotrichum/genetics , Colletotrichum/pathogenicity , Fungal Proteins/genetics , Gene Expression Regulation, Fungal , Hydrogen-Ion Concentration , Polysaccharide-Lyases/genetics , Virulence/geneticsSubject(s)
Granulomatous Disease, Chronic/metabolism , Macrophages/metabolism , Monocytes/metabolism , Oxygen/metabolism , Superoxides/metabolism , Adult , Calcimycin/pharmacology , Cells, Cultured , Female , Humans , Infant , Male , N-Formylmethionine/analogs & derivatives , N-Formylmethionine/pharmacology , N-Formylmethionine Leucyl-Phenylalanine , Oligopeptides/pharmacology , Opsonin Proteins , Tetradecanoylphorbol Acetate/pharmacology , ZymosanABSTRACT
When B10.A (5R) mice (H-12i5) are immunized with spleen cells from congenic B10 mice (H-12b), they respond to alloantigens of the H-2Db region by producing antibodies of only IgM type. In contrast, they produce both IgM and IgG antibodies when immunized with A.BY cells (H-2b) that carry other foreign cell surface antigens (non-H-2) in addition to H-2Db. Preimmunization of 5R mice with two injections of congenic cells leads to an H-2Db specific inhibition of the IgG response to a subsequent immunization with A.BY cells. It is concluded that congenic B10 cells fail to activate helper T cells which are necessary to induce the switch from IgM to IgG production. Instead T- or B-cell tolerance may be induced with prohibits the subsequent IgG response to A.BY cells, possibly by way of suppressor T cells which may act either on B cells directly or via helper T cells.
