Gain-of-Function Phenotypes of Many CLAVATA3/ESR Genes, Including Four New Family Members, Correlate with Tandem Variations in the Conserved CLAVATA3/ESR Domain

Abstract

Secreted peptide ligands are known to play key roles in the regulation of plant growth, development, and environmental responses. However, phenotypes for surprisingly few such genes have been identified via loss-of-function mutant screens. To begin to understand the processes regulated by the CLAVATA3 (CLV3)/ESR (CLE) ligand gene family, we took a systems approach to gene identification and gain-of-function phenotype screens in transgenic plants. We identified four new CLE family members in the Arabidopsis (Arabidopsis thaliana) genome sequence and determined their relative transcript levels in various organs. Overexpression of CLV3 and the 17 CLE genes we tested resulted in premature mortality and/or developmental timing delays in transgenic Arabidopsis plants. Overexpression of 10 CLE genes and the CLV3 positive control resulted in arrest of growth from the shoot apical meristem (SAM). Overexpression of nearly all the CLE genes and CLV3 resulted in either inhibition or stimulation of root growth. CLE4 expression reversed the SAM proliferation phenotype of a clv3 mutant to one of SAM arrest. Dwarf plants resulted from overexpression of five CLE genes. Overexpression of new family members CLE42 and CLE44 resulted in distinctive shrub-like dwarf plants lacking apical dominance. Our results indicate the capacity for functional redundancy of many of the CLE ligands. Additionally, overexpression phenotypes of various CLE family members suggest roles in organ size regulation, apical dominance, and root growth. Similarities among overexpression phenotypes of many CLE genes correlate with similarities in their CLE domain sequences, suggesting that the CLE domain is responsible for interaction with cognate receptors.

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).…”

“…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). Upon exogenous peptide addition or ectopic overexpression in transgenic roots of MtCLE12 and MtCLE13, neither root growth arrest nor enhanced root elongation was observed.…”

“…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).…”

“…This suppressive effect on nodulation was not phenocopied by exogenous application of synthetic peptides. One possible reason could be related to a role for posttranslational hydroxyprolination and subsequent arabinosylation on CLE peptide bioactivity, as suggested for Arabidopsis CLE peptides AtCLE1 to AtCLE7 (Strabala et al, 2006;Ohyama et al, 2009). Moreover, CLV3 arabinosylation has been found to be critical for high-affinity binding to the CLV1 ectodomain (Ohyama et al, 2009).…”

“…CLE peptides with related sequences exhibit redundancy, as proven by similarity in gain-of-function phenotypes (Strabala et al, 2006;Jun et al, 2008). At least two groups of CLE peptides can be distinguished.…”