NOVEL INVENTION OF SPORE INDUCTION IN A SISTER SPECIES TO GROUP 4 DICTYOSTELIA.

Background: Dictyostelia are soil amoebas that aggregate to form fruiting bodies with spores and stalk cells in response to starvation. Where known, species across the dictyostelid phylogeny use secreted cAMP, detected by cAMP receptors (cARs) to induce the differentiation of spores and to organize fruiting body construction. However, recent deletion of the single of ) left both its fruiting bodies and spores intact.

Methods: To investigate whether sporulation can occur in the absence of secreted cAMP and to explore alternative inducers in a bioassay three prespore genes were identified and gene fusions of their promoters with the reporter gene were transformed into cells. After assessing the spatial expression pattern of the genes and the stage at which prespore gene expression initiated, the effect of cAMP and other ( ) signal molecules were tested on prespore gene expression .

Results: genes , and were identified as homologs of spore coat genes. They were first expressed around 4 h of starvation in aggregation centres and later in the posterior 4/5 of emerging sorogens and the spore head of early fruiting bodies. Cells from dissociated 4 h aggregates and shaken in suspension for 6 h increased prespore- reporter activity 4-fold for and 6-fold for but this increase was at least 5-fold higher when cells were plated on solid substratum for 6 h to develop normally. cAMP had no effect on prespore gene induction and neither had the chemoattractant glorin nor the chemoattractants and differentiation inducers folate, c-di-GMP, DIF-1, GABA, cGMP and 8Br-cAMP.

Conclusions: The lineage uniquely evolved a novel genetic network for synthesis, detection and processing of the signal that triggers its main survival strategy.