The unique evolution of the programmed cell death 4 protein in plants

Shijun Cheng,Daniel R Gallie,Renyi Liu

doi:10.1186/1471-2148-13-199

Abstract

BackgroundThe programmed cell death 4 (PDCD4) protein is induced in animals during apoptosis and functions to inhibit translation and tumor promoter-induced neoplastic transformation. PDCD4 is composed of two MA3 domains that share similarity with the single MA3 domain present in the eukaryotic translation initiation factor (eIF) 4G, which serves as a scaffold protein to assemble several initiation factors needed for the recruitment of the 40S ribosomal subunit to an mRNA. Although eIF4A is an ATP-dependent RNA helicase that binds the MA3 domain of eIF4G to promote translation initiation, binding of eIF4A to the MA3 domains of PDCD4 inhibits protein synthesis. Genes encoding PDCD4 are present in many lower eukaryotes and in plants, but PDCD4 in higher plants is unique in that it contains four MA3 domains and has been implicated in ethylene signaling and abiotic stress responses. Here, we examine the evolution of PDCD4 in plants.ResultsIn older algal lineages, PDCD4 contains two MA3 domains similar to the homolog in animals. By the appearance of early land plants, however, PDCD4 is composed of four MA3 domains which likely is the result of a duplication of the two MA3 domain form of the protein. Evidence from fresh water algae, from which land plants evolved, suggests that the duplication event occurred prior to the colonization of land. PDCD4 in more recently evolved chlorophytes also contains four MA3 domains but this may have resulted from an independent duplication event. Expansion and divergence of the PDCD4 gene family occurred during land plant evolution with the appearance of a distinct gene member following the evolution of basal angiosperms.ConclusionsThe appearance of a unique form of PDCD4 in plants correlates with the appearance of components of the ethylene signaling pathway, suggesting that it may represent the adaptation of an existing protein involved in programmed cell death to one that functions in abiotic stress responses through hormone signaling.

Highlights

The programmed cell death 4 (PDCD4) protein is induced in animals during apoptosis and functions to inhibit translation and tumor promoter-induced neoplastic transformation
The bacterial 30 S ribosomal subunit can identify the initiation codon through base-pairing between the 3′-end of its16 S ribosomal RNA subunit and the Shine-Dalgarno sequence upstream of the initiation codon, the 40 S ribosomal subunit of the eukaryotic 80 S ribosome requires several translation initiation factors for its binding to an mRNA and to identify the initiation codon [1,2,3]. eIF4F, which is composed of eIF4E, eIF4A, and eIF4G, is required to promote 40 S
MA3-domains are present in multiple proteins in plants eIF4G contains a single MA3 domain which in plants, is present at the C-terminus as plant eIF4G lacks the HEAT-3/Mnk-binding domain found in animal eIF4G (Figure 1)

Summary

Introduction

The programmed cell death 4 (PDCD4) protein is induced in animals during apoptosis and functions to inhibit translation and tumor promoter-induced neoplastic transformation. EIF4F, which is composed of eIF4E, eIF4A, and eIF4G, is required to promote 40 S eIF4A binds to two regions of eIF4G that fold into HEAT (Huntington, Elongation Factor 3, PR65/A, TOR). One HEAT domain to which eIF4A binds is present in the middle region of eIF4G (HEAT-1/MIF4G, MIG) which is required for translation while the second is C-distal (eIF4G-MA3, HEAT2/MA3) and serves a regulatory function [14,15,16]. A third, functionally distinct HEAT domain, present in animal eIF4G but absent from plant eIF4G, does not bind eIF4A but does bind Mnk kinase which phosphorylates eIF4E during active translation [17]. The eIF4B and PABP interaction sites overlap with the eIF4A binding site in the HEAT-1/ eIF4G-MIG domain of eIFiso4G more extensively than in eIF4G [19]. EIF4B and PABP compete with eIF4A for binding to the HEAT-1/eIF4G-MIG domain of eIFiso4G in the absence of the HEAT-2/ eIF4G-MA3 domain but not in its presence [19]

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