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SUMMARY:AP2-type transcription factors control the gametophore stem cell i
 dentity  - Tsuyoshi Aoyama\, NIBB\, Japan 
DTSTART:20130125T120000Z
DTEND:20130125T130000Z
UID:TALK42940@talks.cam.ac.uk
CONTACT:Jill Harrison
DESCRIPTION:Stem cells are characterized by their ability to self-renew an
 d give rise to differentiated cells. Formation of several types of stem ce
 lls to produce different types of differentiated cells is properly regulat
 ed during development of multicellular organisms.\n\nThe moss Physcomitrel
 la patens is a good model organism to research how different types of stem
  cell identity are determined. In P. patens\, a single protonema apical st
 em cell is formed from a spore. The protonema apical stem cell exhibits ap
 ical growth and cell division to produce differentiated protonema cells. T
 hese differentiated protonema cells often perform a few additional times o
 f cell division to produce a side branch initial cell. Then the side branc
 h initial cell directly changes its identity to either a protonema apical 
 stem cell or a gametophore apical stem cell. Differentiation of two differ
 ent types of stem cells from side branch initial cells is controlled by tw
 o phytohormones\, auxin and cytokinin. However\, molecular mechanisms for 
 such a stem cell formation has been largely unknown.\n\nHere we show that 
 four AP2-type transcription factors orthologous to Arabidopsis thaliana ei
 ght genes are indispensable for the formation of gametophore apical stem c
 ells from side branch initial cells. We named the four P. patens genes APB
 1\, APB2\, APB3\, and APB4\, based on the initials of their orthologous ge
 nes ANINTEGUMENTA\, PLETHORA\, and BABY BOOM in A. thaliana. Quadruple dis
 ruption of all APB genes blocked gametophore apical stem cell formation\, 
 even in the presence of cytokinin\, which enhances gametophore apical stem
  cell formation in the wild type. Time-lapse observation showed that side 
 branch initial cells do not acquire gametophore apical stem cell identity 
 and directly differentiate into protonema apical stem cells even in the co
 nditions of gametophore apical stem cell induction\, at least based on the
 ir morphology. Signals of APB-YFP fusion proteins were detected in emergin
 g gametophore apical stem cells and continuously detected during gametopho
 re apical stem cell formation\, whereas the signals disappeared during pro
 tonema apical stem cell formation. We conclude that the AP2-type transcrip
 tion factors function as a molecular switch to promote the development of 
 different types of stem cells in P. patens. In addition\, in order to reve
 al how APB genes determine the gametophore stem cell identity\, the transc
 riptome analysis was performed. Overexpression of APB4 gene induced differ
 ent types of gene sets depending on the presence of cytokinin. These data 
 suggest the possibility that APB genes interact with cytokinin signaling a
 nd control specific type of gene sets necessary for gametophore stem cell 
 formation. In addition\, I also would like to talk about recent our approa
 ches to visualize auxin and its transport. In P. patens\, differentiated l
 eaf cells are easily reprogrammed to protonema apical stem cells by the ex
 cision of a leaf. This reprogramming process is controlled by auxin. Both 
 application of anti-auxin and overexpression of a stable form of PpIAA1A i
 nhibited the reprogramming. Excision of a leaf induced the expression of A
 RF11 via the down regulation of miR1219\, miR390\, and TAS3 ta-si RNA. The
 n ARF11 induced the expression of STEMIN gene\, which induce the reprogram
 ming. Although it is demonstrated that auxin is important for these reprog
 ramming processes\, it is still unclear when auxin is accumulated\, where 
 auxin maxima exist\, and how auxin is distributed among cells via auxin po
 lar transport. Then we started to reveal these problems by using new auxin
  sensor and visualizing auxin transporter (PIN and AUX). I also would like
  to discuss about these recent preliminary data.\n
LOCATION:Seminar Room\, Department of Plant Sciences
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