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INRA
24, chemin de Borde Rouge –Auzeville – CS52627
31326 Castanet Tolosan CEDEX - France

Dernière mise à jour : Mai 2018

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UMR 1332 Biologie du Fruit et Pathologie

Team Fruit Surface (SURF)

 

SURF logo
Team leader : Christophe Rothan – Tel. (33)5 57 12 25 32 – Email : christophe.rothan@inra.fr

Christophe ROTHAN (DR)
Cécile BRES (IR)
Johann PETIT (IE)

Research objectives

Our work focuses on the formation and specialization of the tissues that constitute the skin of the fruit. We are interested in the skin because it not only contributes to the attractiveness of the fruit for the consumer (brightness, colour, roughness, etc.) but also constitutes the interface between the fruit and its environment (control of water loss, resistance to pathogens, etc.). The skin is poorly studied and its formation is therefore poorly known. Central questions remain.

How skin formation is regulated and how is it coordinated with the development of other fruit tissues?  How do skin composition and structure affect its properties?

The strategies implemented in SURF group to answer these questions are based in particular on the exploitation of genetic resources (tomato mutant collection) and functional genomics tools that we have previously developed (Just et al., 2013; Garcia et al., 2016), on UMR BFP platforms (Imaging, Metabolome/Lipidome) and on strong collaborations established within a large network of national and international collaborations.

Research Topics

Cuticle and Fruit Surface

During early stages of fruit development, fruit cells will differentiate, be organized into distinct tissues and specialize. In this process, epidermal cells will play a major role in fruit protection by establishing a complex lipid barrier, the cuticle, to guarantee the integrity of the fruit. This outer layer is responsible for a large number of agronomic properties of the fruit such as surface appearance, postharvest shelf-life or resistance to pathogens (Petit et al., 2017).

SURF - Ill1

The cuticle is the external lipidic layer covering epidermal cells. A. external cell layers from a tomato peel; B. electron microscopy of tomato peel outer cell layers; C. Bodipy staining of the cuticle, with the major cuticle roles indicated; D. simplified biosynthesis pathway of the cuticular compounds.

Through a direct genetic approach (positional cloning, sequencing mapping) using a collection of tomato EMS mutants in the miniature variety Micro-Tom that we generated previously, we isolated and characterized mutants affected in key genes for cuticle biosynthesis, such as Slcyp86a69 (Shi et al., 2013), Slgpat6-a (Petit et al., 2016; Philippe et al., 2016), Slcus1 (Girard et al., 2012; Petit et al., 2014), and for its regulation, as Slshn2. Cytological, molecular and biochemical analyses carried out on these mutants have already allowed us to get better insights into the formation of the cuticle in the fruit. The establishment of a network of cuticle mutants (double and triple mutants) allows us, in close collaboration with various partners in France and Europe, to deepen our understanding of the regulation of cuticle formation, of the interactions between cuticular compounds and other parietal polymers and of the properties of cuticular polyesters e.g. in pathogen resistance.

Regulation of skin formation and coordination with fruit growth

While the cuticle is the outermost barrier, the skin also includes the epidermis and several underlying cellular layers. The skin is constantly remodeled to ensure the growth of the fruit while maintaining its integrity. Indeed, fruit skin must constantly adapt to fruit enlargement by extending its surface in order to enable the large increase in fruit weight without fruit cracking. To study in more detail the mechanisms involved in these processes, we have extended our investigations to the study of the differentiation and specialization of the epidermis and sub-epidermal cell layers.

The approach chosen is (i) to identify fruit surface mutants not exclusively related to cuticle alteration, in order to acquire additional information on the processes studied, (ii) to identify causal mutations and (iii) to understand their function in skin formation and their role in its properties. Two mutants affected in the epigenetic control of the differentiation of sub-epidermal cells are more particularly studied. The mutation of a HISTONE METHYLASE in the SPOTTED mutant causes an alteration in the specialization of sub-epidermal cells and cuticle formation while the mutation of a HISTONE DEMETHYLASE in the rough mutant causes the ectopic proliferation of sub-epidermal cells which form callus-like structures at the surface of the fruit.  This study allowed us to highlight the major role of the PRC2 polycomb complex and, more broadly, of histone methylation in tomato skin development. This question is central to our current research aimed at the understanding of fruit skin formation

SURF - Ill2

The rough and SPOTTED tomato mutants show fruit surface alterations (A, B) due to cell proliferation on fruit surface in the rough mutant (C) and to ectopic chloroplast accumulation in sub-epidermal cells in the SPOTTED mutant (D).

SURF - Ill3

A: Confocal microscope analysis of a skin section of the SPOTTED tomato mutant showing chloroplast proliferation (red), loss of cell adhesion (blue) and increased cuticle thickness (green) in spotted regions from 20 DPA fruits. B: H3K27me3 histone marks (ChIP seq analysis) of a locus from wild-type (WT) and SPOTTED fruits.