Fig. 5. Pattern formation within the shoot promeristem. (A) pPIN1::PIN1-GFP expression (green) was upregulated in the superficial layer of shoot meristem progenitor cells marked by pCUC2::3XVENUS-N7 reporter expression (red), and in labeled primordium initials (I₁ and I₂). (B) After 24 hours, primordium initials grew into primordia (P₁ and P₂) and pCUC2::3XVENUS-N7 (red) was expressed in the meristem boundaries. (C) PIN1-GFP protein was (green) polarized towards the apex of the shoot progenitors (arrows) and away from peripheral cells marked by the pWUS::DsRed-N7 reporter (blue). (D) Early pREV::REV-VENUS expression (red) was observed in the center of the progenitors underneath the pPIN1::PIN1-GFP (green) domain. Chlorophyll autofluorescence is in blue. (E) 24 hours later in the same developing meristem, pREV::REV-VENUS expression (red) was expressed in the adaxial sides of initiating primordia (I₁ and I₂), and (F) was similarly expressed in primordia within later stage shoot meristems. (G-I) pFIL::DsRed-N7 expression (red) was upregulated in areas flanking the early pPIN1::PIN1-GFP (green) domain (G) and was later upregulated on the abaxial side of early primordia (H) and older primordia (I). (J) pSTM::STM-VENUS (blue) was expressed in a ring surrounding shoot progenitors and a subset of cells within the promeristem (11 days on SIM) while local pPIN1::PIN1-GFP reporter (green) upregulation marked sites of primordium initiation (I₁ and I₂). pWUS::DsRed-N7 reporter (red) was expressed in peripheral cells and upregulated in the center of the developing meristem. (K,L) 24 hours later in the same shoot progenitors, pSTM::STM-VENUS (blue) was upregulated within the meristem between the developing primordia (P₁ and P_2; K) and was maintained through 48 hours of imaging during which primordia grew and two new primordia were initiated (I₁ and I₂; L). (M) pCLV3::mGFP5-ER expression (green) was absent from shoot progenitors marked by pPIN1::PIN1-CFP expression (white) and peripheral cells marked by the pWUS::DsRed-N7 reporter (red). (N) pCLV3::mGFP5-ER expression (green) was detected after primordial outgrowth from the periphery of the developing meristem. (O) pCLV3::mGFP5-ER expression (green) was also observed in later stage shoot meristems which expressed a p35S::YFP 29-1 transgene (yellow). Scale bars: 50 µm (A,B,D-O); 5 µm (C).