The plasma membrane proton pump ATPase: the significance of gene subfamilies.

The plasma membrane proton pump ATPase (H(+)-ATPase) plays a central role in transport across the plasma membrane. As a primary transporter, it mediates ATP-dependent H(+) extrusion to the extracellular space, thus creating pH and potential differences across the plasma membrane that activate a large set of secondary transporters. In several species, the H(+)-ATPase is encoded by a family of approximately 10 genes, classified into 5 gene subfamilies and we might ask what can this tell us about the concept, and the evolution, of gene families in plants. All the highly expressed H(+)-ATPase genes are classified into only two gene subfamilies, which diverged before the emergence of present plant species, raising the questions of the significance of the existence of these two well-conserved subfamilies and whether this is related to different kinetic or regulatory properties. Finally, what can we learn from experimental approaches that silence specific genes? In this review, we would like to discuss these questions in the light of recent data

In search of the still unknown function of FW2.2 / CELL NUMBER REGULATOR, a major regulator of fruit size in tomato

The FW2.2 gene is associated with the major Quantitative Trait Locus (QTL) governing fruit size in tomato, and acts by negatively controlling cell division during fruit development. FW2.2 belongs to a multigene family named the CELL NUMBER REGULATOR (CNR) family. The CNR proteins harbour the uncharacterized PLAC8 motif made of two conserved cysteine-rich domains separated by a variable region that are predicted to be transmembrane segments, and indeed FW2.2 localizes to the plasma membrane. Although FW2.2 was cloned more than two decades ago, the molecular mechanisms of FW2.2 action remain unknown. Especially, how FW2.2 functions to regulate cell cycle and fruit growth, and thus fruit size, is yet not understood. We here review the current knowledge on PLAC8containing CNR/FWL proteins in plants, which are described to participate in plant organogenesis and the regulation of organ size, especially in fruits, and in Cadmium resistance, ion homeostasis and/or Ca2+ signalling. Within the plasma membrane, FW2.2 and some CNR/FWL are localized in microdomains, which is supported by recent data from interactomics studies. Hence FW2.2 and CNR/FWL could be involved in a transport function of signalling molecules across membranes, thus influencing organ growth via a cell-to-cell trafficking mechanism.Comment la communication de cellule à cellule régule-t'elle la croissance du fruit

Expression of a Constitutively Activated Plasma Membrane H+-ATPase Alters Plant Development and Increases Salt Tolerance1[C][OA]

The plasma membrane proton pump ATPase (H+-ATPase) plays a major role in the activation of ion and nutrient transport and has been suggested to be involved in several physiological processes, such as cell expansion and salt tolerance. Its activity is regulated by a C-terminal autoinhibitory domain that can be displaced by phosphorylation and the binding of regulatory 14-3-3 proteins, resulting in an activated enzyme. To better understand the physiological consequence of this activation, we have analyzed transgenic tobacco (Nicotiana tabacum) plants expressing either wild-type plasma membrane H+-ATPase4 (wtPMA4) or a PMA4 mutant lacking the autoinhibitory domain (ΔPMA4), generating a constitutively activated enzyme. Plants showing 4-fold higher expression of wtPMA4 than untransformed plants did not display any unusual phenotype and their leaf and root external acidification rates were not modified, while their in vitro H+-ATPase activity was markedly increased. This indicates that, in vivo, H+-ATPase overexpression is compensated by down-regulation of H+-ATPase activity. In contrast, plants that expressed ΔPMA4 were characterized by a lower apoplastic and external root pH, abnormal leaf inclination, and twisted stems, suggesting alterations in cell expansion. This was confirmed by in vitro leaf extension and curling assays. These data therefore strongly support a direct role of H+-ATPase in plant development. The ΔPMA4 plants also displayed increased salt tolerance during germination and seedling growth, supporting the hypothesis that H+-ATPase is involved in salt tolerance

The FW2.2/CNR protein regulates cell-to-cell communication in tomato by modulating callose deposition at plasmodesmata

The FW2.2 gene is the founding member of the CELL NUMBER REGULATOR (CNR) gene family. More than 20 years ago, FW2.2 was the first cloned gene underlying a Quantitative Trait Locus (QTL) governing fruit size/weight in tomato. However, despite this discovery, the molecular mechanisms by which FW2.2 acts as a negative regulator of cell divisions during fruit growth remain undeciphered. In the present study, we confirm that FW2.2 is a transmembrane spanning protein, whose both N-and C-terminal ends are facing the apoplast. We unexpectedly found that FW2.2 is located at plasmodesmata (PD). FW2.2 participates in the spatiotemporal regulation of callose deposition at PD via an interaction with Callose Synthases, which suggests a regulatory role in cell-to-cell communication by modulating PD transport capacity and trafficking of signaling molecules during fruit development

Functional characterization of a new plant DYNAMIN protein controlling cell shape, through actin cytoskeleton dynamics

A forward genetic strategy, combining tomato EMS mutant variability and mapping-by-sequencing (Garcia et al., 2016; Musseau et al., 2017) allowed the identification of a DYNAMIN protein, as a key regulator of tomato fruit tissue morphology. DYNAMINs (DYNs) are large GTPase that can interact with cytoskeleton-associating proteins. In animals, DYNs are reported to be involved in cytokinesis, membrane trafficking, cytoskeletal dynamics and pathogen resistance (Konopka et al., 2006; Praefcke & Mcmahon, 2004). Plants present homologs for most dynamins found in animals, with some proven to be functional redundant. However, the role and molecular mechanisms of this particular dynamin have never been described in plants so far.In order to investigate its role in plants, experiments were conducted in both tomato and Arabidopsis thaliana models. dyn mutants share common aberrant cell size and shape, affecting pericarp cells in tomato and trichomes in Arabidopsis. Aberrant Arabidopsis trichome morphology is strikingly similar to the well described Arabidopsis mutants affected in the WAVE and ARP2/3 pathways, that are involved in actin filament nucleation (Isner et al., 2017; Sambade et al., 2014; Zimmermann et al., 2004). Our data suggest a role of this plant dynamin in actin cytoskeleton remodeling, supporting rapid cell elongation

Functional characterization of a new plant DYNAMIN protein involved in cytoskeleton organization and cell shape

A forward genetic strategy, combining tomato EMS mutant variability and mapping-by-sequencing (Garcia et al., 2016; Musseau et al., 2017) allowed the identification of a DYNAMIN protein, as a key regulator of tomato fruit tissue morphology. DYNAMINs (DYNs) are large GTPase that can interact with cytoskeleton-associating proteins. In animals, DYNs are reported to be involved in cytokinesis, membrane trafficking, cytoskeletal dynamics and pathogen resistance (Konopka et al., 2006; Praefcke & Mcmahon, 2004). Plants present homologs for most dynamins found in animals, with some proven to be functional redundant. However, the role and molecular mechanisms of this particular dynamin have never been described in plants so far.In order to investigate its role in plants, experiments were conducted in both tomato and Arabidopsis thaliana models. dyn mutants share common aberrant cell size and shape, affecting pericarp cells in tomato and trichomes in Arabidopsis. Aberrant Arabidopsis trichome morphology is strikingly similar to the well described Arabidopsis mutants affected in the WAVE and ARP2/3 pathways, that are involved in actin filament nucleation (Isner et al., 2017; Sambade et al., 2014; Zimmermann et al., 2004). Our data suggest a role of this plant dynamin in actin cytoskeleton remodeling, supporting rapid cell elongation

Elucidating the functional role of endoreduplication in tomato fruit development

International audienceBackgroundEndoreduplication is the major source of endopolyploidy in higher plants. The process of endoreduplication results from the ability of cells to modify their classical cell cycle into a partial cell cycle where DNA synthesis occurs independently from mitosis. Despite the ubiquitous occurrence of the phenomenon in eukaryotic cells, the physiological meaning of endoreduplication remains vague,although several roles during plant development have been proposed, mostly related to cell differentiation and cell size determination.ScopeHere recent advances in the knowledge of endoreduplication and fruit organogenesis are reviewed, focusing on tomato (Solanum lycopersicum) as a model, and the functional analyses of endoreduplication-associated regulatory genes in tomato fruit are described.ConclusionsThe cyclin-dependent kinase inhibitory kinase WEE1 and the anaphase promoting complex activator CCS52A both participate in the control of cell size and the endoreduplication process driving cell expansion during early fruit development in tomato. Moreover the fruit-specific functional analysis of the tomato CDK inhibitor KRP1 reveals that cell size and fruit size determination can be uncoupled from DNA ploidy levels, indicating that endoreduplication acts rather as a limiting factor for cell growth. The overall functional data contribute to unravelling the physiological role of endoreduplication in growth induction of fleshy fruits

Functional characterization of a new plant DYNAMIN protein involved in cytoskeleton organization and cell shape

A forward genetic strategy, combining tomato EMS mutant variability and mapping-by-sequencing (Garcia et al., 2016; Musseau et al., 2017) allowed the identification of a DYNAMIN protein, as a key regulator of tomato fruit tissue morphology. DYNAMINs (DYNs) are large GTPase that can interact with cytoskeleton-associating proteins. In animals, DYNs are reported to be involved in cytokinesis, membrane trafficking, cytoskeletal dynamics and pathogen resistance (Konopka et al., 2006; Praefcke & Mcmahon, 2004). Plants present homologs for most dynamins found in animals, with some proven to be functional redundant. However, the role and molecular mechanisms of this particular dynamin have never been described in plants so far.In order to investigate its role in plants, experiments were conducted in both tomato and Arabidopsis thaliana models. dyn mutants share common aberrant cell size and shape, affecting pericarp cells in tomato and trichomes in Arabidopsis. Aberrant Arabidopsis trichome morphology is strikingly similar to the well described Arabidopsis mutants affected in the WAVE and ARP2/3 pathways, that are involved in actin filament nucleation (Isner et al., 2017; Sambade et al., 2014; Zimmermann et al., 2004). Our data suggest a role of this plant dynamin in actin cytoskeleton remodeling, supporting rapid cell elongation