COMPARATIVE ANALYSIS OF LUMINESCENCE INTENSITY OF SINGLE SPORE ISOLATES FROM THE NATURALLY BIOLUMINESCENT FUNGUS ARMILLARIA MELLEA (AGARICALES, PHYSALACRIACEAE)

Abstract

Bioluminescence is the production and emission of light by a living organism which requires the oxidation of a luciferin substrate by a luciferase enzyme or photoprotein to produce light. Nearly all the described fungi that bioluminesce are mushroom-forming, saprotrophic species belonging to four, distantly related lineages in the Agaricales (Basidiomycota). Here, I conduct comparative studies to examine the variation in luminescence intensity of single spore isolates (SSIs) of the bioluminescent fungus, Armillaria mellea. A diploid isolate of A. mellea was inoculated on sawdust, rice and tomato media and incubated to induce formation of basidiomata in vitro. Luminescence intensity of single spore isolates (SSIs) from haploid basidiospores were obtained and classified as three phenotypes (bright, dim and intermediate) based on their luminescence intensity. Three bright (>1000 AUs), four intermediate (200-999 AUs) and three dim SSIs (<200 AUs) were selected for pairings in the following combinations: i) bright bright; ii) intermediate intermediate and; iii) dim dim luminescence intensity. In addition, dim and bright luminescent isolates were paired with a non-luminescent transformant obtained from the USDA-ARS. The frequency and luminescence intensity of haploid SSIs (n = 241) obtained from matings from five compatible mycelial pairings that produced basidiomata and matured to generate viable basidiospores [bright bright (n = 2), intermediate intermediate (n = 1), dim transformant (n = 2)] and differences in luminescence intensity were compared at 14, 23 and 32 days post inoculation (dpi). Mean luminescence intensity of SSIs obtained from bright bright matings were greater than SSIs obtained from intermediate intermediate and dim transformant matings. The differences in mean luminescence intensity suggests that the expression of bioluminescence is a heritable trait and exhibits a continuous distribution in luminescence intensity. In addition, matings of bright bright isolates produced a higher frequency of SSIs with bright luminescence intensity (92%); however, 50% of SSIs obtained from the intermediate intermediate cross and 21% of SSIs generated from the dim transformant crosses exhibited bright luminescence intensity. This suggests that bioluminescence is a complex trait involving the interactions of multiple genes.