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


Author for correspondence: Uwe K. Simon Tel: +49 7071 2976689 Fax: +49 7071 295344 Email:


  • • 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 β-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 β-1,3-glucans, the IA itself is considered an apoplastic compartment.