Bioluminescence expression during the transition from mycelium to mushroom in three North American Armillaria and Desarmillaria species

Unlike most bioluminescent fungi, mycelia of Armillaria and Desarmillaria are constitutively bioluminescent while mature mushrooms are not. The absence of the luciferin, 3-hydroxyhispidin, and its precursor hispidin in mature mushrooms have been proposed to explain the lack of bioluminescence from Armillaria mushrooms. Using three North American species, A. gallica, A. mellea and D. tabescens (syn., Armillaria tabescens), we documented a decline in luminescence of ten fold during the transition from mycelia to, immature mushrooms (i.e., pins) for the two Armillaria species. As pins matured, luminescence declined by an additional two or three orders of magnitude. Lower initial luminescence of D. tabescens mycelia declined to negligible levels during mushroom development. Further, light production was localized in the gills and lower stipe of A. mellea mushrooms. The decline in luminescence during mushroom formation was reversed by addition of hispidin to stipe or gills which significantly enhanced luminescence by one and three orders of magnitude, respectively. We conclude that the modulation of Armillaria and Desarmillaria luminescence is achieved by luciferin availability early in mushroom development. However, since the temporal regulation of bioluminescence differs between Armillaria species and other genera, we conclude that bioluminescence in Armillaria is under unique selective pressures.