Loss of pectin is an early event during infection of cocoyam roots by Pythium myriotylum

• Published in: Planta Vol. 223; no. 2; pp. 271 - 282
• Main Authors: Boudjeko, T, Andeme-Onzighi, C, Vicre, M, Balange, A.P, Ndoumou, D.O, Driouich, A
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 2006; Springer; Springer Nature B.V
• Subjects: Agronomy. Soil science and plant productions; Antibodies; Apposition; Biological and medical sciences; callose; Cell Wall - chemistry; Cell Wall - microbiology; Cell Wall - ultrastructure; Cell walls; cellulose; Cellulose - analysis; Economic plant physiology; Epidermal cells; Fundamental and applied biological sciences. Psychology; Fungi; galacturonic acid; Glucans - analysis; Hexuronic Acids - isolation & purification; Hexuronic Acids - metabolism; host-pathogen relationships; Hyphae; Infections; Microscopy, Electron, Transmission; pectins; Pectins - analysis; Pectins - metabolism; Plant Diseases - microbiology; plant morphology; plant pathogenic fungi; Plant roots; Plant Roots - metabolism; Plant Roots - microbiology; Plant Roots - ultrastructure; Plant tissues; Plants; Pythium - growth & development; Pythium - pathogenicity; Pythium myriotylum; root rot; soil fungi; staple foods; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Xanthosoma - microbiology; Xanthosoma - physiology; Xanthosoma - ultrastructure; Xanthosoma sagittifolium; Xylans - analysis; xyloglucans; Monocotyledones; Root; Immunocytochemistry; Tropical zone; Phycomycetes; Cellulose; Pythium myriotylum; Pectin; Cell wall; Callose; Fungi; Rot disease; Araceae; Angiospermae; Tuber; Xanthosoma sagittifolium; Spermatophyta; Thallophyta; Cocoyam
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-005-0090-2

Cocoyam (Xanthosoma sagittifolium) is an important tuber crop in most tropical zones of Africa and America. In Cameroon, its cultivation is hampered by a soil-borne fungus Pythium myriotylum which is responsible for root rot disease. The mechanism of root colonisation by the fungus has yet to be elucidated. In this study, using microscopical and immunocytochemical methods, we provide a new evidence regarding the mode of action of the fungus and we describe the reaction of the plant to the early stages of fungal invasion. We show that the fungal attack begins with the colonisation of the peripheral and epidermal cells of the root apex. These cells are rapidly lost upon infection, while cortical and stele cells are not. Labelling with the cationic gold, which binds to negatively charged wall polymers such as pectins, is absent in cortical cells and in the interfacial zone of the infected roots while it is abundant in the cell walls of stele cells. A similar pattern of labelling is also found when using the anti-pectin monoclonal antibody JIM5, but not with anti-xyloglucan antibodies. This suggests that early during infection, the fungus causes a significant loss of pectin probably via degradation by hydrolytic enzymes that diffuse and act away from the site of attack. Additional support for pectin loss is the demonstration, via sugar analysis, that a significant decrease in galacturonic acid content occurred in infected root cell walls. In addition, we demonstrate that one of the early reactions of X. sagittifolium to the fungal invasion is the formation of wall appositions that are rich in callose and cellulose.