Detoxification of phytoanticipins and phytoalexins by phytopathogenic fungi

Abstract

Most plants synthesize antimicrobial compounds as part of normal plant development (i.e., phytoanticipins) or synthesize such compounds de novo when challenged by microorganisms (i.e., phytoalexins). The presumed role of these plant antibiotics is to protect the plant from disease. However, many phytopathogenic fungi have enzymes that can detoxify the phytoanticipins or phytoalexins produced by their host. This may be a means that these pathogens have evolved to circumvent resistance mechanisms based on the production of plant antibiotics. Many of the phytoanticipin- and phytoalexin-detoxifying enzymes produced by phytopathogenic fungi have biochemical and regulatory properties that would indicate the phytoanticipins and phytoalexins produced by their host are their normal substrates. In addition, their activity, enzymatic products, or transcripts can be detected in infected plant tissue suggesting that they are functioning in planta during pathogenesis. Specific mutations have been made by transformation-mediated gene-disruption procedures that eliminate the ability of Gaeumannomyces graminis var. avenae, Gloeocercospora sorghi, and Nectria haematococca to detoxify the phytoanticipins or phytoalexins produced by their hosts. The effect of these mutations on pathogenicity indicates a requirement for detoxifying enzymes in G. graminis var. avenae but not in G. sorghi or N. haematococca. Key words: disease resistance, pathogenicity mechanisms, isoflavonoids, saponins, cyanide.

In planta sequential hydroxylation and glycosylation of a fungal phytotoxin: Avoiding cell death and overcoming the fungal invader

“…43% of the initial amount of 1 detected after incubation for 110 h. On the other hand, a contrasting trend was observed for the metabolism of hydroxydestruxin B (3) to ␤-D-glucosyl hydroxydestruxin B (5); cultivars of B. napus (S) appeared to transform hydroxydestruxin B (3) to 5 substantially faster than cultivars of S. alba (R), whereas Cutlass (B. juncea, S) showed an intermediate rate. Most importantly, leaf and cell culture assays showed that hydroxydestruxin B (3) was substantially less toxic to any of the species tested than destruxin B (1), and ␤-D-glucosyl hydroxydestruxin B (5) showed no toxicity at all ( Table 2).…”

“…Consequently, such detoxification traits are desirable and of much importance in strategic plant breeding or in engineering disease resistance. Whereas a number of phytoalexin detoxifying reactions have been shown to occur in very diverse plant pathogenic fungi (1,5,6), detoxification of phytotoxins has been reported in only a few plant species (7).…”

Detoxification of Corn Antimicrobial Compounds as the Basis for Isolating Fusarium verticillioides and Some Other Fusarium Species from Corn

“…Fungal detoxification of plant antimicrobial compounds is known to enhance virulence and in some associations is essential for pathogenicity (8,11,43,50,52). Determining if a correlation exists between benzoxazinoid detoxification and fungal virulence depends on measurement of in planta aspects of infection, colonization, and compatibility.…”

Preformed Antimicrobial Compounds and Plant Defense against Fungal Attack.

“…However, whereas preformed inhibitors may be effective against a broad spectrum of potential pathogens, successful pathogens are likely to be able to circumvent the effects of these antibiotics either by avoiding them altogether or by tolerating or detoxifying them (Schonbeck and Schlosser, 1976;Fry and Myers, 1981;Bennett and Wallsgrove, 1994;VanEtten et al, 1995;Osbourn, 1996). The isolation of plant mutants defective in the biosynthesis of preformed inhibitors would allow a direct genetic test of the importance of these compounds in plant defense.…”