Plant CLE peptides from two distinct functional classes synergistically induce division of vascular cells

Abstract

The Clavata3 (CLV3)/endosperm surrounding region (CLE) signaling peptides are encoded in large plant gene families. CLV3 and the other A-type CLE peptides promote cell differentiation in root and shoot apical meristems, whereas the B-type peptides (CLE41-CLE44) do not. Instead, CLE41 inhibits the differentiation of Zinnia elegans tracheary elements. To test whether CLE genes might code for antagonistic or synergistic functions, peptides from both types were combined through overexpression within or application onto Arabidopsis thaliana seedlings. The CLE41 peptide (CLE41p) promoted proliferation of vascular cells, although delaying differentiation into phloem and xylem cell lineages. Application of CLE41p or overexpression of CLE41 did not suppress the terminal differentiation of the root and shoot apices triggered by A-type CLE peptides. However, in combination, A-type peptides enhanced all of the phenotypes associated with CLE41 gain-of-function, leading to massive proliferation of vascular cells. This proliferation relied on auxin signaling because it was enhanced by exogenous application of a synthetic auxin, decreased by an auxin polar transport inhibitor, and abolished by a mutation in the Monopteros auxin response factor. These findings highlight that vascular patterning is a process controlled in time and space by different CLE peptides in conjunction with hormonal signaling.cambium ͉ hypocotyl ͉ RAM ͉ SAM ͉ TDIF I n higher plants, postembryonic organogenesis is mediated by meristems. These specialized structures provide a reservoir of undifferentiated stem cells as well as a limited population of proliferating cells, often referred to as transit-amplifying (TA) cells that are fated for differentiation (1). To date, molecular research has focused on the Arabidopsis primary meristems of root and shoot apices, but more recent studies have sought to dissect molecular programs underpinning the control of secondary meristems, including the vascular cambium (2, 3) that is a circumferential stem cell niche including the fusiform initials from which secondary xylem and phloem originate (2). During the course of differentiation, fusiform initial daughters take on a TA state to increase the population of xylem and phloem mother cells. Positioning and size of stem cell and TA cell populations, at least in root and shoot meristems, are controlled in a noncell-autonomous manner (1,4,5).This noncell-autonomous control of stem cell size and positioning has best been described in Arabidopsis primary meristems where a stable pool of undifferentiated stem cells are maintained by a feedback loop mechanism involving the Clavata (CLV) signaling pathway and the Wuschel (WUS) homeodomain transcription factor (6, 7). Similar regulatory mechanisms may be at work within root meristems, where the transcription factor WUS-related-homeobox 5 (WOX5) controls stem cell maintenance (8) and CLV3 and related genes can influence root patterning (9-11), although to date the regulation of WOX5 by a CLV-like pathway has not been demonstrated...

CLE Peptides Control Medicago truncatula Nodulation Locally and Systemically

“…MtCLE12 and MtCLE13 are most similar to a group of less characterized Arabidopsis CLE peptides (AtCLE1-AtCLE7) that are broadly produced with higher activity levels in the root (Sharma et al, 2003;Ito et al, 2006). Exogenous peptide addition did not suppress procambial-to-xylem cell transdifferentiation in a zinnia cell culture, while application of high, but not low, concentrations of peptides resulted in primary root meristem arrest (Ito et al, 2006;Strabala et al, 2006;Kinoshita et al, 2007;Whitford et al, 2008). Furthermore, ectopic overexpression of this group of peptides resulted in root elongation, mild wus loss-of-function phenotypes, mild distorted leaves, and dwarfing in later growth stages (Strabala et al, 2006).…”

“…Studies on the putative CLE peptides of Arabidopsis (Ito et al, 2006;Ni and Clark, 2006;Strabala et al, 2006;Whitford et al, 2008) have shown a direct relationship between CLE domain sequence and induced phenotypes. MtCLE12 and MtCLE13 are most similar to a group of less characterized Arabidopsis CLE peptides (AtCLE1-AtCLE7) that are broadly produced with higher activity levels in the root (Sharma et al, 2003;Ito et al, 2006).…”

“…Members of group II, exemplified by TDIF, prevent cellular differentiation, as evidenced by the suppression of procambium-to-xylem transdifferentiation in zinnia (Zinnia elegans) cell cultures, and control the rate and orientation of vascular cell division (Ito et al, 2006;Etchells and Turner, 2010). Although these studies would suggest two groups with opposing functions, synergistic actions between these groups of peptides have been demonstrated (Whitford et al, 2008). In Arabidopsis, the proliferation of vascular precursor cells induced by the group II CLE41 peptides is enhanced by the addition of CLE6 peptides that otherwise have an inhibiting effect on root growth when applied at high concentrations and thus belong to group I.…”

RGF1 INSENSITIVE 1 to 5, a group of LRR receptor-like kinases, are essential for the perception of root meristem growth factor 1 in Arabidopsis thaliana

“…TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF)/ CLE41/CLE44 peptide regulates vascular development in Arabidopsis. TDIF peptide derived from CLE41 or CLE44 is perceived by PHLOEM INTERCALATED WITH XYLEM (PXY), an LRR-RLK [21][22][23][24].…”

A Tale of Two Systems: Peptide Ligand-Receptor Pairs in Plant Development

“…This approach indeed established TDR/PXY as a CLE41/44 receptor in the regulation of vascular stem cells (Hirakawa et al 2008). The overexpression of CLE41 resulted in pleiotropic phenotypes, including a dwarf appearance with numerous bushy, small leaves, suggesting that CLE41/44 is involved in many biological processes other than vascular meristem maintenance (Whitford et al 2008).…”