Fig. 6: A schematic outline showing the potential effect of positive selection on the melanin biosynthetic gene cluster in L. rhizohalophila. PKS2 catalyzes the first step of melanin biosynthesis.
From: Divergence of a genomic island leads to the evolution of melanization in a halophyte root fungus
The use of melanin biosynthesis inhibitors (tricyclazole and kojic acid, 50 μg mL−1) confirmed that L. rhizohalophila synthesized dihydroxynaphthalene melanin (DHN-melanin), as colonies growing in the presence of kojic acid, the inhibitor of dihydroxyphenyalanine (DOPA) melanin, appeared normal and were indistinguishable from the controls. The representative isolates from group 1 and group 2 grown on PDA without NaCl for two weeks at 25 °C are shown. Positive selection acting on this genomic island results in the fixation of many beneficial non-synonymous mutations. Using antiSMASH 5.0, the cluster organization (six genes) and PKS2 domains, including KS, AT, ACP, and TD were predicted in silico. The proposed model of melanin metabolism involving melanin biosynthesis (PKS2 and MSHR), membrane trafficking (MFS), regulation (two transcription factors), localization, and deposition (loosening of cell wall regulated by expansin) is shown. PKS polyketide synthase, MSHR melanocyte-stimulating hormone receptor, MFS major facilitator superfamily, TF transcription factors, EXP expansin, THN tetrahydroxynaphthalene.
