Fig. 7. Apical patterning during embryogenesis. (A-D) Mutant phenotypes. (A,B) Apical region of the early-heart stage embryo. (A) Wild-type apex is divided into three subregions, presumptive SAM (PS; orange), cotyledon primordia (CP; yellow) and boundary of cotyledon margins (BCM; blue). (B) In the pin1-3 or pin1-3 pid-2 embryo, the peripheral region possesses a mixed identity of CP and BCM, which is shown in green. (C,D) Late heart stage. The area of BCM is reduced in pin1-3 (C), while the entire peripheral region continues to express a mixed identity of CP and BCM in pin1-3 pid-2 (D). (E,F) Model for apical patterning during embryogenesis. (E) PID expression (blue) accumulates mainly in the boundaries of cotyledon primordia and slightly in regions that surround the base of cotyledon primordia. PIN1 and PID redundantly promote auxin transport toward the tips of the cotyledon primordia (brown arrows), resulting in the formation of auxin gradient maxima (green). (F) Auxin accumulation in cotyledon primordia (green) prevents CUC gene expression (yellow) from expanding to the periphery.