The Regulation Of TDIF Peptide Hormone In Poplar Growth And Development

TDIF（Tracheary Element Differentiation Inhibitory Factor）peptide was originally identified in the Zinnia elegans L.culture system as an extracellular dodecapeptide factor that could regulate the division of（pro）cambium cells and the differentiation of xylem cells in vascular tissues.Previously,6 genes have been identified in the genome of Populus trichocarpa as the closest Populus orthologs of Arabidopsis CLE41/CLE44 genes.Among them,Pt TDIF1-4 encode a dodecapeptide as exactly same as TDIF,and Pt TIDFL1-2encode a TDIF-like（TDIFL）peptide with one amino acid variation.The q RT-PCR analysis showed that six Pt TDIFs genes were all expressed in shoot vascular tissues.In Arabidopsis Pt TDIFpro:GUS lines,the expression driven by Pt TDIFs promoters were predominantly detected in stem vascular bundles,the SAM,leaf primordia and leaf veins.Overexpression of Pt TDIF2 and Pt TDIFL2 genes in hybrid poplar（Populus tremula×P.alba）severely retarded the internodal elongation by upregulating GA2ox and GA20ox genes and thus decreasing the level of endogenous GA₁and GA₄,and this phenotypic defect could be rescued by exogenously applied GA₃.Pt TDIFs-overexpressing(Pt TDIFs^OE)unexpectedly induced a more complex venation pattern in poplar leaves,which was underpinned by the elevated expression of WOX4 and WOX13 genes.In addition,top shoots of 35S:Pt TDIFs trees revealed a higher IAA level and a stronger IAA biosynthetic capacity.If the aerial tissues of transgenic plants were removed to prevent auxin transportation from top to bottom,the phenotype of increased lateral roots could be significantly inhibited,indicating that auxin transportation in plants was necessary for this phenotype.35S:Pt TDIFs poplars displayed an increased susceptibility for exogenous IAA,and N-1-naphthylphthalamic acid（NPA）could completely block the TDIF-induced LR formation.In Pt TDIFs^OEroots,several auxin-related LR initiation markers such as GATA23,ACR4,LBD16 and LBD29 were transcriptionally upregulated.This study not only revealed the regulatory mechanism of TDIF peptide on internode elongation,leaf vein formation and lateral root generation in poplar,but also further enriched the network model of the interaction between various hormone signals by exploring the synergistic effect of TDIF and other plant hormones in different tissues and organs.