MAP-ping genomic organization and organ-specific expression profiles of poplar MAP kinases and MAP kinase kinases

Marie-Claude Nicole,Louis-Philippe Hamel,Brian E Ellis,Marie-Josée Morency,Nathalie Beaudoin,Armand Séguin

doi:10.1186/1471-2164-7-223

Abstract

BackgroundAs in other eukaryotes, plant mitogen-activated protein kinase (MAPK) cascades are composed of three classes of hierarchically organized protein kinases, namely MAPKKKs, MAPKKs, and MAPKs. These modules rapidly amplify and transduce extracellular signals into various appropriate intracellular responses. While extensive work has been conducted on the post-translational regulation of specific MAPKKs and MAPKs in various plant species, there has been no systematic investigation of the genomic organization and transcriptional regulation of these genes.ResultsTen putative poplar MAPKK genes (PtMKKs) and 21 putative poplar MAPK genes (PtMPKs) have been identified and located within the poplar (Populus trichocarpa) genome. Analysis of exon-intron junctions and of intron phase inside the predicted coding region of each candidate gene has revealed high levels of conservation within and between phylogenetic groups. Expression profiles of all members of these two gene families were also analyzed in 17 different poplar organs, using gene-specific primers directed at the 3'-untranslated region of each candidate gene and real-time quantitative PCR. Most PtMKKs and PtMPKs were differentially expressed across this developmental series.ConclusionThis analysis provides a complete survey of MAPKK and MAPK gene expression profiles in poplar, a large woody perennial plant, and thus complements the extensive expression profiling data available for the herbaceous annual Arabidopsis thaliana. The poplar genome is marked by extensive segmental and chromosomal duplications, and within both kinase families, some recently duplicated paralogous gene pairs often display markedly different patterns of expression, consistent with the rapid evolution of specialized protein functions in this highly adaptive species.

Highlights

As in other eukaryotes, plant mitogen-activated protein kinase (MAPK) cascades are composed of three classes of hierarchically organized protein kinases, namely MAPK kinase kinase (MAPKKK), MAPKKs, and MAPKs
Genomic distribution of poplar MAPK and MAPKK genes Previous analysis of the genome sequence of poplar (Populus trichocarpa) had identified robust gene models corresponding to all the MAPK (PtMPK) and MAPKK (PtMKK) family members [39]
Our work demonstrates that differential spatiotemporal transcript accumulation patterns exist for most members of both the MPK and the MKK gene families in poplar

Summary

Introduction

Plant mitogen-activated protein kinase (MAPK) cascades are composed of three classes of hierarchically organized protein kinases, namely MAPKKKs, MAPKKs, and MAPKs. Members of the mitogen-activated protein kinase family are involved in major signaling pathways in all eukaryotes [1] These pathways, which are typically activated by intracellular or environmental cues, usually consist of three hierarchically organized protein kinases. The phosphorylated MAPKK acts as a dual-specificity protein kinase to activate the third component of the pathway, i.e. MAPK, via phosphorylation of specific threonine and tyrosine residues in a T-X-Y motif located within the activation loop of the protein. At this point, activated MAPKs can modulate various cellular activities through activation of other protein kinases, or metabolic enzymes, or by phosphorylation of transcription factors and components of the cytoskeleton. Important links between MAPK activities and fundamental processes like cell proliferation/differentiation and defence responses have been established from extensive studies performed in human, mouse and yeast systems [2]

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