Regulated expression of the MADS-box transcription factor SrfA mediates activation of gene expression by protein kinase A during Dictyostelium sporulation.

Cell differentiation and morphogenesis are tightly regulated during sporulation in the lower eukaryote Dictyostelium discoideum. The control of the cyclic adenosine monophosphate (cAMP)-dependent protein kinase is essential to coordinate these processes. Several signal transduction pathways are being recognized that lead to the regulation of intracellular cAMP levels. However, very little is known about the events lying downstream of that are essential to activate late gene expression and terminal differentiation of the spores. We have studied the relationship between duanyu1529 and the MADS-box transcription factor SrfA, essential for spore differentiation. Constitutive activation of duanyu1529 was not able to rescue sporulation in a strain that lacks srfA suggesting the possibility that srfA functions downstream of duanyu1529 in a signal transduction pathway leading to spore maturation. A distal promoter region regulates the induction of srfA expression in the prespore region during culmination. We found that this promoter can be induced precociously by activating duanyu1529 with 8-Br-cAMP suggesting a transcriptional regulation by Moreover, precocious sporulation and expression of the spore marker spiA in a strain that overexpresses correlates with a precocious induction of srfA expression. The temporal and spatial pattern of expression was also studied in a mutant strain lacking the main adenylyl cyclase that functions during culmination, ACR. This strain is expected to have lower duanyu1529 activity and consistently, the level of srfA expression was reduced. Moreover, the temporal induction of srfA in the prespore region was also delayed during culmination. Our results strongly suggest that duanyu1529 activation during culmination leads to the induction of the expression of srfA. The correct temporal and spatial pattern of srfA expression appears to be part of a mechanism that ensures the adequate coordination of gene expression and morphogenesis.

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