Regulation of the G2 arrest during the infection process in the pathogenic fungus Ustilago maydis.

NATALIA MIELNICHUK, CECILIA SGARLATA & JOSÉ PÉREZ-MARTÍN

Madrid

Congreso; Zimomadrid XXI; 2007

Ustilago maydis undergoes a cell cycle arrest at G2 phase in response to pheromone stimulation (García-Muse et al., 2003). This cell cycle arrest is maintained after cell fusion by an unknown mechanism regulated by the bW/bE transcription factor. To study how the b heterodimer regulates this cell cycle arrest we took advantage of the AB33 strain in which the expression of the b transcription factor is induced by NO3 (Brachmann et al., 2001). Using this genetic background, we found that a Cdk1 version refractory to inhibitory phosphorylation could not maintain the cell cycle arrest, resulting in filament carrying more than one nucleus. Considering the role of b protein as a transcriptional regulator, we analyzed the variation at transcriptional level of different cell cycle regulators like Wee1, Cdc25, Hsl1, Plk1, 14-3-3 when the b protein was induced. However, these changes were not enough to explain the cell cycle arrest. Moreover, the constitutive expression of some regulators of G2/M transition phase, like Clb1 and Plk1, uncoupled from b transcriptional regulation could only count for low percentages of unarrested nuclei. These results suggest that regulatory protein interactions like cellular localization and activation of Cdc25 or Wee1 could be involved in the regulation of the cell cycle arrest signalled by the b protein.  Possible regulatory mechanism will be discussed.