The Mechanism Study On The Regulation Of Plant Meristem Activity By Poplar CLE Signaling Molecular

The CLE(CLAVATA3/EMBRYO SURROUNDING REGION)gene family are important short-range mobile ligands that mediate intercellular communication to maintain stem cell homeostasis and regulate postembryonic organogenesis.Plant CLE proteins usually include an N-terminal signal peptide for secretion,a C-terminal conserved CLE motif composed of 12-14 amino acids,and an intervening highly variable domain of unknown function.It plays a pivotal role in regulating in various aspects of plant development,especially in shoot apical meristem(SAM),root apical meristem(RAM)and procambium.However,in the model plant of xylophyta like poplar,the functions of CLE peptide gene family are little known.In this work,among 50 CLE gene family members in the Populus trichocarpa genome,three and six PtCLE genes encode a CLE motif sequence highly homologous to Arabidopsis CLV3 and TDIF peptides,respectively,which potentially make them functional equivalents.To test and compare their biological activity,we first chemically synthesized each dodeca-peptide and analysed its in vitro bioactivity on Arabidopsis seedlings.Similarly,but to a different extent,three types of poplar CLV3-related peptides caused root meristem consumption,phyllotaxis disorder,anthocyanin accumulation and failure to enter the bolting stage.In comparison,application of two poplar TDIF-related peptides led to root length promotion in a dose-dependent manner with an even stronger effect observed for poplar TDIF-like peptide than TDIF.Next,we constructed CaMV35S:PtCLE transgenic plants for each of the nine PtCLE genes.Phenotypic abnormalities exemplified by arrested shoot apical meristem and abnormal flower structure were found to be more dominant and severe in 35S:PtCLV3 and 35S:PtCLV3-like2 lines than in the 35S:PtCLV3-like1 line.Disordered vasculature was detected in both stem and hypocotyl cross-sections in Arabidopsis plants over-expressing poplar TDIF-related genes with the most defective vascular patterning observed for TDIF2 and two TDIF-like genes.Phenotypic difference consistently observed in peptide application assay and transgenic analysis indicated the functional diversity of nine poplar PtCLE genes under investigation.This work represents the first report on the functional analysis of CLE genes in a tree species and constitutes a basis for further study of the CLE peptide signalling pathway in tree development.