Plant organellar protein targeting: a traffic plan still under construction

Abstract

It has long been understood that specific features of a protein and its corresponding import apparatus dictate the behavior of mitochondrial proteins in their intracellular targeting behavior. In plants, the process by which proteins are directed to organelles has been influenced uniquely by the introduction to the cell of plastids. Parallel functions carried out within the mitochondrion and plastid permit the sharing of proteins and emergence of mechanisms to facilitate dual-targeting of the nuclear-encoded products to both compartments. These include transcriptional and translational variations, relaxation of translation initiation controls and conditional cellular influences. Details of the dual targeting system are emerging from recent studies, and evidence of variation in protein targeting behavior across plant families and across organisms implies that the system itself is in flux. This trend towards multi-targeting enhances protein versatility across eukaryotes -one means of cellular response to developmental or environmental influence.

Arabidopsis Photorespiratory Serine Hydroxymethyltransferase Activity Requires the Mitochondrial Accumulation of Ferredoxin-Dependent Glutamate Synthase

“…In recent years, it has become clear that a number of proteins encoded by nuclear genes are dual targeted, with the chloroplasts/mitochondria being the most common dual destinations (Silva-Filho, 2003;Mackenzie, 2005). Dual plastid/mitochondrion targeting can be achieved either with twin presequences or with an ambiguous presequence.…”

“…An increasing number of examples have been described in which proteins are dual targeted to both the chloroplast and mitochondrion (Small and Peeters, 2001;Mackenzie, 2005). Dual targeting is typically accomplished by the presence of tandem chloroplastic and mitochondrial targeting sequences or else by the presence of an ambiguous presequence that is recognized by the import apparatus of both organelles.…”

Translational Landscape of Photomorphogenic Arabidopsis

“…Indeed, several studies have demonstrated that translational regulation could occur at various levels. These include alternative translation initiation with one transcript producing two proteins targeted to different organelles, microRNA (miRNA)-mediated repression of translation by pausing ribosomes or accelerating ribosome drop-off, and lower reinitiation efficiency of main open reading frames (mORFs) by the translation of upstream open reading frames (uORFs) in the 59 untranslated region (UTR) (reviewed in Morris and Geballe, 2000;Mackenzie, 2005;Fabian et al, 2010;Huntzinger and Izaurralde, 2011). To fully understand translational regulation, we need to measure the dynamic positional information and abundance of translating ribosomes on a transcript.…”

Participation of Leaky Ribosome Scanning in Protein Dual Targeting by Alternative Translation Initiation in Higher Plants

“…Several examples exist of plant genes encoding proteins targeted to both mitochondria and plastids (Mackenzie, 2005). However, one might hypothesize that the process of protein dual targeting is subject to some degree of cellular regulation to control relative protein stoichiometries in different tissues.…”