Metabolism of the Flavonoid Epicatechin by Laccase of Colletotrichum gloeosporioides and Its Effect on Pathogenicity on Avocado Fruits

Abstract

During avocado fruit ripening, decreasing levels of the flavonoid epicatechin have been reported to modulate the metabolism of preformed antifungal compounds and the activation of quiescent Colletotrichum gloeosporioides infections. Epicatechin levels decreased as well when C. gloeosporioides was grown in the presence of epicatechin in culture. Extracts of laccase enzyme obtained from decayed tissue and culture media fully metabolized the epicatechin substrate within 4 and 20 h, respectively. Purified laccase protein from C. gloeosporioides showed an apparent MW of 60,000, an isoelectric point at pH 3.9, and maximal epicatechin degradation at pH 5.6. Inhibitors of fungal laccase such as EDTA and thioglycolic acid reduced C. gloeosporioides symptom development when applied to ripening susceptible fruits. Isolates of C. gloeosporioides with reduced laccase activity and no capability to metabolize epicatechin showed reduced pathogenicity on ripening fruits. On the contrary, Mexican isolates with increasing capabilities to metabolize epicatechin showed early symptoms of disease in unripe fruits. Transcript levels of cglac1, encoding C. gloeosporioides laccase, were enhanced during fungal development in the presence of epicatechin at pH 6.0, where avocado fruits are susceptible to fungal attack. But transcript increase was not detected at pH 5.0, where the fruit is resistant to fungal attack. The present results suggest that biotransformation of epicatechin by C. gloeosporioides in ripening fruits is followed by the decline of the preformed antifungal diene compound, resulting in the activation of quiescent infections.

Extracellular enzymes ofColletotrichum fructicola isolates associated to Apple bitter rot and Glomerella leaf spot

“…It is known that products of pectin breakdown act as a second inducer of LAC, (Guetsky et al 2005). In addition, LACs have been known for its influence on enzymatic degradation of lignin, fungal virulence (Lin et al 2012) and help fungi to eliminate toxic plant metabolites (Guetsky et al 2005).…”

“…It is known that products of pectin breakdown act as a second inducer of LAC, (Guetsky et al 2005). In addition, LACs have been known for its influence on enzymatic degradation of lignin, fungal virulence (Lin et al 2012) and help fungi to eliminate toxic plant metabolites (Guetsky et al 2005). These metabolites, such as, polyphenols, phytoalexins and other fungitoxic substances present or induced, differ markedly during leaf and fruit development (Terry et al 2004).…”

“…Although these enzymes are markedly important in some anthracnose diseases (Guetsky et al 2005), their role in pathogens that cause leaf diseases has not been established so far. In fact, causes of the lower activity found in vivo could be associated to the alkaline environment needed for gene expression and subsequently secretion of some extracellular enzymes.…”

“…Laccase (LAC), also known as p-diphenol oxidase, is another extracellular enzyme widely found in fungi, and has a variety of biological activities, such as, lignin degradation (Baldrian 2006), detoxification of antifungal compounds, suppression of plant defence responses (Chi et al 2009), fungal virulence and appressorial melanisation (Guetsky et al 2005; Lin et al 2012). LAC has an important role in pathogenicity by detoxifying epicatechin in avocado and capsaicin in chilli pepper infected by C. gloeosporioides (Guetsky et al 2005; Liao et al 2012).…”

“…LAC has an important role in pathogenicity by detoxifying epicatechin in avocado and capsaicin in chilli pepper infected by C. gloeosporioides (Guetsky et al 2005; Liao et al 2012). …”