Study of the function of FW2.2, a plasmodesmata-located protein

FW2.2 est un QTL majeur contrôlant jusqu'à 30 % de la variation de la taille des fruits. FW2.2 agit comme régulateur négatif de la division cellulaire mais son role reste incertain. Pendant ma thèse, des plantes gain et perte de fonction et des lignées rapportrices GUS sous le promoteur FW2.2 ont été générées pour étudier le mécanisme de régulation de FW2.2. Nous avons démontré que FW2.2 est localisé aux plasmodesmes, des ponts intercellulaires qui assurent une continuité cytosolique directe entre deux cellules. Les plantes gain de fonction montrent une augmentation de la diffusion de cellule à cellule dans la feuille. Le niveau de dépôt de callose a été mesuré à deux stades de développement du fruit et une augmentation du dépôt de callose a été observée chez les plantes perte de fonction. A l’inverse, le niveau de dépôt de callose diminue lorsque FW2.2 est surexprimé, ce qui suggère un rôle de FW2.2 dans la régulation du niveau de dépôt de callose pour contrôler la communication cellulaire.FW2.2 was identified first as a major QTL controlling for up to 30% of the fruit weight variation. FW2.2 is a negative regulator of cell division but its function remains unclear. Here, gain- and loss-of-function plants and GUS reporter lines under FW2.2 promoter were generated to investigate its mode of action. We demonstrated that FW2.2 is localised to plasmodesmata, a channel that provide direct cytosolic continuity between two cells. Gain-of-function plant show an increase in cell-to-cell diffusion in leaf. Level of callose deposition was measured at two different developmental stages of fruit development and an increase of callose was reported in loss-of-function plant. On the contrary, level of callose deposition decrease when FW2.2 is overexpressed suggesting a role of FW2.2 in callose deposition/degradation to control cell-to-cell communication

Etude de la fonction de FW2.2, une protéine localisée aux plasmodesmes

FW2.2 est un QTL majeur contrôlant jusqu'à 30 % de la variation de la taille des fruits. FW2.2 agit comme régulateur négatif de la division cellulaire mais son role reste incertain. Pendant ma thèse, des plantes gain et perte de fonction et des lignées rapportrices GUS sous le promoteur FW2.2 ont été générées pour étudier le mécanisme de régulation de FW2.2. Nous avons démontré que FW2.2 est localisé aux plasmodesmes, des ponts intercellulaires qui assurent une continuité cytosolique directe entre deux cellules. Les plantes gain de fonction montrent une augmentation de la diffusion de cellule à cellule dans la feuille. Le niveau de dépôt de callose a été mesuré à deux stades de développement du fruit et une augmentation du dépôt de callose a été observée chez les plantes perte de fonction. A l’inverse, le niveau de dépôt de callose diminue lorsque FW2.2 est surexprimé, ce qui suggère un rôle de FW2.2 dans la régulation du niveau de dépôt de callose pour contrôler la communication cellulaire.FW2.2 was identified first as a major QTL controlling for up to 30% of the fruit weight variation. FW2.2 is a negative regulator of cell division but its function remains unclear. Here, gain- and loss-of-function plants and GUS reporter lines under FW2.2 promoter were generated to investigate its mode of action. We demonstrated that FW2.2 is localised to plasmodesmata, a channel that provide direct cytosolic continuity between two cells. Gain-of-function plant show an increase in cell-to-cell diffusion in leaf. Level of callose deposition was measured at two different developmental stages of fruit development and an increase of callose was reported in loss-of-function plant. On the contrary, level of callose deposition decrease when FW2.2 is overexpressed suggesting a role of FW2.2 in callose deposition/degradation to control cell-to-cell communication

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

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