Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2015 Dec 9;6:1052. doi: 10.3389/fpls.2015.01052

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

Copyright © 2015 Hepworth and Pautot.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

PMC Copyright notice

Summary of hormone profiles and genetic interactions that maintain the leaf-SAM boundary. (A) The shoot apex contains: the meristem, the initium, boundaries, and organ primordia. The predicted distribution of key hormones are summarized (see text for details). Meristem, high CK/IAA ratio and low GA/BR ratio promotes indeterminate growth. Primordia, high IAA activates BR and represses CK biosynthesis and GA increases to promote determinate growth. Boundary, depletion for growth-promoting hormones IAA, GA, BR, and CK inhibits cell division allowing separation of meristem-organ compartments. I, Initium; CK, cytokinin; BR, brassinosteroid; GA, gibberellin; and IAA, auxin. (B) Summary of gene networks at the meristem-boundary interface. Meristem, STM maintains indeterminate growth by promoting CK and repressing GA/BR accumulation (black gradient indicates hormone abundance). Auxin, shown in green, marks the site of primordia initiation and distal blade of emerging leaf. (1) KNOX proteins initialize the boundary through promotion of BR catabolic genes (BAS1) and boundary transcription genes including CUC and BOP2 (blue arrows). CUC factors confer boundary identity required for activation of other classes of boundary regulators including BOP, KNAT-BELL, LOF1, ALOG, and LBD members that collectively restrict growth, modulate meristematic activity, and pattern the boundary. PIN1 auxin eﬄux carriers (green circles) are orientated facing outward such that auxin is drained away from the boundary. Green arrows indicate direction of auxin flow. (2) Boundary genes contribute to meristem maintenance (see text). (3) STM-BELL meristem factors preserve meristem integrity by restricting BOP1/2 and KNAT6 to boundaries. BR-activated transcription factor BZR1 represses CUC/LOF1 in the meristem domain. (C) Summary of interactions at the leaf-boundary interface. (1) Polar auxin transport establishes auxin maxima in the peripheral zone where leaf initiation takes place. Auxin response factor MP initiates primordium formation by repressing KNOX genes, activating ANT members and leaf identity genes including AS1 and stimulating synthesis of BR where BZR1 binds to the ANT promoter as a positive regulator. Boundary genes BOP1/2 and JLO expressed in the organ initial contribute to organ polarity and stable repression of KNOX genes. (2) Primordium outgrowth coincides with synthesis of auxin and repolarization of PIN transports toward the leaf base, which becomes a low IAA/BR domain. BOPs and JLO now restricted to the boundary reinforce this pattern in hormones via regulation of LOB and PIN1, respectively. CIN-TCPs and BZR1 in leaves maintain repression of CUC/LOF1. JAG in the distal blade represses BOPs. BOPs expressed in the proximal petiole domain of leaves maintain organ polarity and repress KNOX and JAG genes required for simple leaf shape indirectly in part via activation of AS2. YAB contributes to the repression of KNOX and CUC in the abaxial domain.