The intercellular biotrophic leaf pathogen Cymadothea trifolii locally degrades pectins, but not cellulose or xyloglucan in cell walls of Trifolium repens

• DOI: 10.1111/j.1469-8137.2004.01233.x
• Publication Date: 2004-12-28T05:00:27Z
• Authors: Uwe K. Simon; Robert Bauer; Danny Rioux; Marie Simard; Franz Oberwinkler
• Keywords: 0106 biological sciences; Ascomycota; Cell Wall; Hyphae; Pectins; Trifolium; Xylans; Cellulose; Glucans; Immunohistochemistry; 01 natural sciences; Plant Diseases

The intercellular ascomycetous pathogen Cymadothea trifolii, causing sooty blotch of clover, proliferates within leaves of Trifolium spp. and produces a complex structure called interaction apparatus (IA) in its own hyphae. Opposite the IA the plant plasmalemma invaginates to form a bubble. Both structures are connected by a tube with an electron-dense sheath. Using immunocytochemistry on high-pressure frozen and freeze-substituted samples, we examined several plant and fungal cell wall components, including those in new host wall appositions at the interaction site, as well as a fungal polygalacturonase. Within the tube linking IA and host bubble, labelling was obtained for cellulose and xyloglucan but not for rhamnogalacturonan-I and homogalacturonans. The IA labelled for chitin and beta-1,3-glucans, and for a fungal polygalacturonase. Plant wall appositions reacted with antibodies against callose, xyloglucans and rhamnogalacturonan-I. Cymadothea trifolii partly degrades the host cell wall. Structural elements remain intact, but the pectin matrix is dissolved. A fungal polygalacturonase detected in the IA is probably a key factor in this process. Owing to the presence of chitin and beta-1,3-glucans, the IA itself is considered an apoplastic compartment.