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Introduction to Fungi, Third Edition

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382 HYMENOASCOMYCETES: PYRENOMYCETES<br />

Fig12.46 The biosynthetic pathway<br />

of fungal melanin via DHN<br />

(dihydroxynaphthalene). A polyketide<br />

synthase fuses five acetate units<br />

head-<strong>to</strong>-tail followed by cyclization,<br />

resulting in the pentaketide<br />

1,3,6,8 -tetrahydroxynaphthalene.<br />

This is modified by two reductases<br />

and two dehydratases <strong>to</strong><br />

1,8 -dihydroxynaphthalene.This melanin<br />

precursor, which is presumably<br />

synthesized in the cy<strong>to</strong>plasm, is<br />

released in<strong>to</strong> the wall and then<br />

polymerized <strong>to</strong> melanin by wall-bound<br />

oxidases, presumably laccases.<br />

Melanin biosynthesis is an excellent<br />

target for fungicides, and the points<br />

of inhibition of several of them are<br />

indicated. Based partly on Uesugi (1998)<br />

and Thompson et al. (2000).

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