WOX going on: CLE peptides in plant development

Abstract

The development of plant tissues requires cell-cell communication facilitated by chemical and peptide hormones, including small signaling peptides in the CLAVATA3/EMBRYO-SURROUNDING REGION (CLE) family. The paradigmatic CLE signaling peptide CLAVATA3 regulates the size of the shoot apical meristem and the expression of the stem cell-promoting WUSCHEL transcription factor through an unknown mechanism. This review discusses recent advances in CLE signaling, showing that CLE pathways are conserved in bryophytes, that CLE peptides in Arabidopsis thaliana regulate stem cell identity and cell division in root tissues, and connections to auxin biosynthesis in regulating flower and leaf development. These advances shed light on potential WUSCHEL family-independent aspects of CLE signaling and the overlap between CLE and auxin signaling.

Keywords: Auxin; CLAVATA; CLE peptide; Meristem; Plant development; Receptor kinase; WOX.

Figure 1:

CLEs regulate specific cell populations of the RAM The RAM is composed of many different cell types displayed in (A) (From left to right, Lateral Root Cap (LRC), Epidermis, Columella, Cortex, Cortex/Endodermal Initial (CEI), Endodermis (En), Pericycle, Protophloem lineage cells, Procambium, and Xylem lineage cells). CLEs and their receptors regulate aspects of root development; (B) shows cell types regulated by CLE/Receptor combinations.

Figure 2:

CLE control of the SAM and lateral shoot organs The inflorescence meristem is a SAM that produces flowers from the peripheral zone, and the ability of the central zone to maintain the peripheral zone is regulated by the organizing center (A). Although many LRR-RLK mutants have enlarged SAMs and seem to act in the CLV3 pathway, only CLV1 and to a lesser degree the BAMs likely directly perceive CLV3 in the organizing center (B). The epidermis of cotyledons is composed of pavement cells and stomata (C). bam1/2/3 mutants have impaired leaf shape and vascular development (Scale bar .5cm) (D). Meristemoids are stomatal lineage stem cells that can produce stomata guard cells as well as additional pavement cells; CLE9/10 control stomatal spacing divisions of the meristemoids (E). The inner layers of leaves are composed of a variety of cell types, including the vascular bundles containing vascular cambium, regulated by TDIF/TDR signaling (F).