The role of beta-carotene derivatives in speciation and communication in zygomycete fungi

Sexual development and morphogenesis in the fungal class Zygomycetes is regulated by a complex mixture of apocarotenoids, the trisporoids. To date, five derivates, A-E of trisporic acid and its precursors are known. Despite extensive interspecific sexual reactions, species specificity of mating and delimitation of species is ensured. Recognition of specific distribution patterns of trisporoid derivates is one probable cause of this phenomenon.

With the trisporoid derivates, we are studying the emergence of metabolic diversity and its maintenance using a combination of physiological, biochemical and genetical approaches. Besides establishing the derivate pattern in selected species and substrate specificity of the enzymes involved in biosynthesis, we investigate the effects of pure, synthetically prepared derivates and analogues and compare these effects between different species. In Mucor mucedo, e.g. the B derivate of trisporic acid and the precursor trisporin shows a higher effectivity in the induction of sexually determined hyphae and in the feed-back carotene induction than the C and A/C derivates, respectively. In general, the specific action of trisporoids depends highly on the overall dimensions and the configuration at the ring moiety of the respective compounds. Modifications at the isoprenoid side chain are of minor importance. To approach the degradation of beta-carotene as primary step for the introduction of diversity in trisporoid synthesis, we analyse an active carotene dioxygenase active in Rhizopus oryzae, the only sequenced zgyomycete, and identified the corresponding gene in Blakeslea trispora.

The project is rounded off with functional and genetic analyses of one of the biosynthesis enzymes, 4-dihydromethyltrisporate dehydrogenase, also extending to the more distantly related species. Studies of TDH and its gene TSP1 in several species revealed the occurence of species-specific regulation patterns regarding gene and protein activity.

The combined data are analysed with regard to any indication of interrelation between the evolution of metabolic diversity and formation of species. Because of their tendency towards horizontal gene transfer, zygomycetes may well apply alternative mechanisms of diversification. Reconstruction of the evolutionary history within the Mucorales shows the genealogy for TSP1 to be extremely different from that of a multigene phylogram. Bioinfomatic analyses identified Chaetocladium jonesii and Mucor rouxii as putative donors for horizontal gene transfer.

References

[back]