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Front. Plant Sci. | doi: 10.3389/fpls.2018.00565

Chimeric structure of plant malic enzyme family: different evolutionary scenarios for NAD- and NADP-dependent isoforms.

 Marcos A. Tronconi1*, Carlos S. Andreo1 and  Maria F. Drincovich1
  • 1Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Argentina

Malic enzyme (ME) comprises a family of proteins with multiple isoforms located in different compartments of eukaryotic cells. In plants, cytosolic and plastidic enzymes share several characteristics such as NADP specificity (NADP-ME), oxaloacetate decarboxylase (OAD) activity and homooligomeric assembly. However, mitochondrial counterparts are NAD-dependent proteins (mNAD-ME) lacking OAD activity, which can be structured as homo and hetero-oligomers of two dissimilar subunits. In this study, we examined the molecular basis of these differences using multiple sequence analysis, structural modeling and phylogenetic approaches. Plant mNAD-MEs show the lowest identity values when compared with other eukaryotic MEs with major differences including short amino acid insertions distributed throughout the primary sequence. Some residues in these exclusive segments are co-evolutionarily connected, suggesting they could be important for enzymatic functionality. Phylogenetic analysis indicates that eukaryotes from different kingdoms used different strategies for acquiring the current set of NAD(P)-ME isoforms. In this sense, while the full gene family of vertebrates derives from the same ancestral gene, plant NADP-ME and NAD-ME isoforms are not evolutionary related. Plant NADP-ME genes may have arisen from the α-protobacterial-like mitochondrial ancestor, a characteristic shared by eukaryotes mayor taxa. On the other hand, plant mNAD-ME genes were probably gained through an independent process involving the Archaeplastidia ancestor. Finally, several residue signatures unique to all plant mNAD-MEs could be identified, some of which also might be functionally connected to the exclusive biochemical properties of these isoforms. In light of these results, molecular evolutionary scenarios for these widely distributed enzymes in plants are discussed.

Keywords: phylogeny, malic enzyme, land plants, molecular evolution, NAD or NADP specificity

Received: 13 Dec 2017; Accepted: 10 Apr 2018.

Edited by:

Jean Rivoal, Université de Montréal, Canada

Reviewed by:

Jeffrey C. Waller, Mount Allison University, Canada
Dave Speijer, University of Amsterdam, Netherlands
Sebastien Renaut, Other  

Copyright: © 2018 Tronconi, Andreo and Drincovich. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Marcos A. Tronconi, Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Rosario, Argentina, tronconi@cefobi-conicet.gov.ar