Abstract
A stem cell is undifferentiated type of cell that self-renews and also gives rise to a cell to be differentiated. Formation of several types of stem cells to produce different types of differentiated cells is properly regupated during development of multicellular organisms. We found that PpAPB1, 2, 3, and 4 transcription factors in the AP2/ERF family regulate the characterization of a stem cell in the moss Physcomitrella patens. In P.patens, a side branch initial cell differentiates to a gametophore stem cell or a protonemal stem cell. Gametophore stem cells are induced by exogenous cytokinin in the wild type, while the quadruple disruptants of the PpAPBs did not form any gametophore stem cells with exogenous cytokinin application. Furthermore, conditional expression of PpAPB4 promoted gametophore formation. Unexpectedly, the expression of PpAPB genes was induced by auxin instead of cytokinin. These results suggest that the PpAPB genes under auxin signaling are indispensable for the characterization of a gametophore stem cell synergistically with cytokinin signaling. We will discuss the roles of PpAPB genes, auxin, and cytokinin in stem cell characterization.
