No abstract

Summary Biotrophic plant pathogenic fungi are one of the major causes of crop losses. The infection processes they exhibit are typified by infected host plant cells remaining alive for several days. This requires the development of specialized infection structures such as haustoria which are produced by obligate biotrophs, and intracellular hyphae which are produced by many hemibiotrophs. These infection hyphae are surrounded by the host plant plasma membrane, and in the case of haustoria the extrahaustorial membrane differs biochemically and structurally from the normal membrane. An interfacial matrix separates haustoria and intracellular hyphae from the invaginated membrane and this seems to be characteristic of biotrophic interactions. There is clear evidence for molecular differentiation of the haustorial plasma membrane in powdery mildews and rusts in comparison with the other fungal membranes. Relatively few pathogenicity genes related to biotrophy, and the switch from biotrophy to necrotrophy in hemibiotrophs, have been identified.

SummaryThe monoclonal antibody, UB25, recognises a glycoprotein specifically located at the biotrophic interface formed in the Colletotrichum lindemuthianum-bean interaction. The antibody labels the walls of intracellular hyphae and the interfacial matrix which separates them from the invaginated host plasma membrane. In Western blots, UB25 recognises a ladder of bands which are multiples of M r 40.5 kDa. A full length cDNA encoding the glycoprotein recognised by UB25 has been isolated by expression cloning and designated CIH1 (Colletotrichum Intracellular Hypha 1). In vitro transcription/translation of CIH1, and transfection of mammalian COS cells, showed that UB25 recognised the expressed product in both procedures confirming that the clones isolated were true positives. Southern analysis of bean and C. lindemuthianum genomic DNA indicated that the CIH1 glycoprotein is fungally encoded and Northern analysis showed that it is only expressed in planta. Analysis of the deduced amino acid sequence of CIH1 indicates the presence of an N-terminal signal sequence and two possible sites for N-glycosylation. The N-terminal domain of the mature protein is rich in proline and contains several short repetitive motifs. CIH1 is thus a fungal proline-rich glycoprotein which appears to form a cross-linked structure in planta and, as such, resembles plant cell wall proline-and hydroxyproline-rich proteins. Possible functions for the CIH1 protein in the establishment and maintenance of biotrophy are discussed.