Evolution of self-organisation in Dictyostelia by adaptation of a non-selective phosphodiesterase and a matrix component for regulated cAMP degradation

Abstract

SUMMARYDictyostelium discoideum amoebas coordinate aggregation and morphogenesis by secreting cyclic adenosine monophosphate (cAMP) pulses that propagate as waves through fields of cells and multicellular structures. To retrace how this mechanism for selforganisation evolved, we studied the origin of the cAMP phosphodiesterase PdsA and its inhibitor PdiA, which are essential for cAMP wave propagation. D. discoideum and other species that use cAMP to aggregate reside in group 4 of the four major groups of Dictyostelia. We found that groups 1-3 express a non-specific, low affinity orthologue of PdsA, which gained cAMP selectivity and increased 200-fold in affinity in group 4. A low affinity group 3 PdsA only partially restored aggregation of a D. discoideum pdsA-null mutant, but was more effective at restoring fruiting body morphogenesis. Deletion of a group 2 PdsA gene resulted in disruption of fruiting body morphogenesis, but left aggregation unaffected. Together, these results show that groups 1-3 use a low affinity PdsA for morphogenesis that is neither suited nor required for aggregation. PdiA belongs to a family of matrix proteins that are present in all Dictyostelia and consist mainly of cysteine-rich repeats. However, in its current form with several extensively modified repeats, PdiA is only present in group 4. PdiA is essential for initiating spiral cAMP waves, which, by organising large territories, generate the large fruiting structures that characterise group 4. We conclude that efficient cAMPmediated aggregation in group 4 evolved by recruitment and adaptation of a non-selective phosphodiesterase and a matrix component into a system for regulated cAMP degradation.

Evolution of developmental signalling in Dictyostelid social amoebas

“…Spiral waves organize larger territories and hence give rise to large aggregates and robust fruiting bodies [41, 42]. PdiA belongs to a matrix protein family, but only has true orthologs in group 4, while groups 1–3 PdsAs have a 200-fold lower affinity for cAMP than D. discoideum PdsA, and only partially restore aggregation of a D. discoideum pdsA null mutant [43]. The use of cAMP as chemoattractant in group 4 and its association with robust aggregation and fruiting body formation therefore depended both on changes in PdsA protein function, recruitment of a matrix protein as a PdsA inhibitor and changes in carA gene expression.…”

“…Early aggregating prototypes use secreted cAMP accumulating in aggregates as a signal for spore formation [39]. In early Dictyostelia, an emerging network of CarA, AcaA and PdsA produces cAMP pulses to coordinate fruiting body morphogenesis [38, 43]. Finally, group 4 acquires DIF-1 as a signal for basal disc formation, while addition of distal ‘early’ promoters to carA and acaA genes, and increased affinity of PdsA enables the use of cAMP as chemoattractant for aggregation in group 4 [38, 43, 48].…”

A set of genes conserved in sequence and expression traces back the establishment of multicellularity in social amoebae

“…DD spore formation is evolutionary derived from encystation, sharing a core signalling pathway [33, 34]. From the above set, we selected five genes for knock-out by homologous recombination (Additional file 3: Figure S4).…”

A Conserved Signalling Pathway for Amoebozoan Encystation that was Co-Opted for Multicellular Development

“…The first fragment was reduced to 2.4 kb by XbaI/BglII digest and inserted into XbaI/BamHII digested vector pLox-NeoIII14. The second fragment was digested with HindIII/KpnI, using restriction sites introduced in the primers, and inserted into the HindIII/KpnI sites of the newly generated vector pAcgA-KO (Supplementary figure 3).…”