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					          Lecture 4

Planar Polarity: The Pavement
         Cell System
         Tongda Xu    QuickTime™ and a
                        decompressor
                are neede d to see this picture.




Shingo
Nagawa

                                                   Hongjiang Li
How do cells “talk” to each another to coordinate
  their polarity, growth, and morphogenesis?
*Arabidopsis
                                                                                    Coordinated
                                                                                    cell growth      How is local
                                                                                     in stems        coordination
                                                                                                     achieve?

                                                                                       Pavement      What is the global
                                                                                       cells with
            Qui ckTi me™ an d a
 T IFF (Uncomp re sse d) d ecomp re ssor
     are ne ede d to see thi s pi ctu re .                                          interdigitated
                                                                                                     signal?
                                                                                       lobes and
                                                                                     indentations    How is the global
                                                                                                     signaling to
                                                                                    Coordinated      linked to the local
                                                        QuickTime™ and a
                                             TIF F (U ncompr essed) decompr essor
                                                                                        PIN1         coordination?
                                                are needed to see this pictur e.    localization
                                                                                    to the basal
                                                                                         end
       Interdigitation of Leaf Pavement Cells (PCs)
  •      A process of cell intercalation involving cell-cell coordination
         of morphogenesis
  •      Outgrowth in lobe-forming regions must be coordinated with
         restriction of outgrowth in complementary indenting regions


      View from the leaf surface


                                                                         c   m
                                                                     Q ui k Ti e™ and a
                                                           TI FF ( Unc om pr es s ed) dec om pr es s or
                                                                                       s   c
                                                              ar e ne eded t o s ee t hi pi t ur e.




Indentation     Lobe
                                              Convergent
                                              extension in
 PC intercalation in leaves                 animal embryos
      Intercalary pavement cells: a model system
         for the study of cytoskeletal signaling

   Input             Subcellular mediator:           Output
                       The cytoskeleton
                                              •Cell polarity,
•Developmental,                               •Polar growth,
•Hormonal,                                    •Cell shape changes
•Intercellular &   ???                        •Spatiotemporal
•Environmental                                control of cell
Signals                  Microtubules (MTs)   division




                         Filamentous actin
                              (F-actin)
  base                                     tip
                                                    base                                      tip




•How are alternating lobes and indents within a
cell coordinately formed?




                                                           are neede d to see this picture.
                                                                 QuickTime™ and a
                                                                   decompressor
•How are lobing and indenting coordinated locally
between neighboring cells?
•How is the interdigitation process coordinated
globally in the entire leaf?
     Rop: the sole subfamily of Rho small
             GTPases from plants

                    RhoBHs                     Rho2 Sc
                  RhoCHs          Rho1 Sc
                RhoAHs

                                            Rho
                                                          ROP: Rho-like
                              Fungi &                     GTPase from
  RacRa c1 Hs
          Rac2 Hs
                              animals                     plants
   Cdc4 2 Sc
 Cdc4 2 bHs                            Rop7
  Cdc4 2 pHs                                  Rop6
Cdc42          Rop8                         Rop2         Arabidopsis
                                           Rop4
                                           Rop5
                  Rop9
                      Rop11
                                      Rop1
                                          Rop3
                                            pollen          ROP
                              Rop10




                 Zheng & Yang. 2000. Plant Mol Biol. 44:1-9
ROP2/4 promotes lobe formation in
         pavement cells




                                 rop4-1,ROP2(RNAi)

             Abnormal               Inhibition
            outgrowth in           outgrowth in
               necks                  lobes

                Fu et al. 2002. Plant Cell 14:763-776
     ROP2/ROP4 locally activate actin assembly
      and suppress microtubule organization
                                                                        ROP2/4

                RIC4
                                                                                                                                    RIC1
    153 a.a.    CRIB
                                                                                 CRIB                                                        224 a.a.


                                                                                                c    m
                                                                                             Q ui k Ti e™ and a
                                                                                   TI FF ( Unc om pr es s e d) dec om pr e s s or




Fine cortical
                                                                                                                s   c
                                                                                      ar e ne eded t o s ee t hi pi t ur e.


                                    c m
                                 Q ui k Ti e™ and a
                       TI FF ( Unc om pr es s e d) dec om pr e s s or
                                                    s c
                          ar e ne eded t o s ee t hi pi t ur e.




                                                                                                                                            Transverse
 actin MFs                                                                                                                                 Cortical MTs




                Fu et al. 2005. Cell 120:687-800
ROP6 promotes indenting and suppresses lobing by
   activating RIC1-dependnet MT organization
                                                       GFP-RIC1 localization




                                          ROP6 OX or
 TI FF ( U
               c m
            Q ui kTi e™ and a
          ncom pr essed) decom pr essor
    ar e needed t o see t hi pi t ur e.
                           s c
                                          rop2 rop4



                                           rop6
                                                              TI FF ( U
                                                                             c m
                                                                          Q ui kTi e™ and a
                                                                       ncom pr essed) decom pr essor
                                                                  ar e needed t o see t hi pi t ur e.
                                                                                         s c
                                                                                                        rop2 rop4 or
                                                                                                        ROP6 OX
                           Fine
Lobing                      F-
Signal                     Actin   Lobe
         RIC4                                       Indenting
      ROP2                                            signal

ROP2 GTP                                                   Neck
GDP                                             RIC1ROP6
                           RIC1         RIC1
                                             ROP6        ROP2
                                                                ROP2
       Lobing Signal                                                       ROP2
                                   MT                   ROP6 ROP6          RIC4
                                                                    ROP6   actin
                                                                    RIC1
  Localized ROP2 activation                                         MT



      RIC4         RIC1       ROP6         Indenting
                                           Signal
  Localized Transverse MT
  Actin MFs arrangement
                                          Fu et al. 2005. Cell 120:687-800
                                          Fu et al. 2009. Cur Bio, Accepted
      Intercalary growth
                                Fine
Lobing                         F-Actin
Signal?                                  Lobe
                                                              Indenting
             RIC4
                                                               signal?
          ROP2
          GTP
ROP2                                                                 Neck
GDP                                                      RIC1 ROP6
                             RIC1               RIC1
          Lobing Signal                                ROP6

                                         MT
   Localized ROP2 activation

       RIC4          RIC1      ROP6           Indenting Signal

   Localized Transverse MT
   Actin MFs arrangement

      Intercalary growth

				
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