Analyses of Tomato Fruit Brightness Mutants Uncover Both Cutin-Deficient and Cutin-Abundant Mutants and a New Hypomorphic Allele of GDSL Lipase

Johann Petit,Christophe Rothan,Jérôme Joubès,Virginie Garcia,Bénédicte Bakan,Jean-Philippe Mauxion,Cécile Bres,Didier Marion,Daniel Just,Frédéric Domergue

doi:10.1104/pp.113.232645

Abstract

The cuticle is a protective layer synthesized by epidermal cells of the plants and consisting of cutin covered and filled by waxes. In tomato (Solanum lycopersicum) fruit, the thick cuticle embedding epidermal cells has crucial roles in the control of pathogens, water loss, cracking, postharvest shelf-life, and brightness. To identify tomato mutants with modified cuticle composition and architecture and to further decipher the relationships between fruit brightness and cuticle in tomato, we screened an ethyl methanesulfonate mutant collection in the miniature tomato cultivar Micro-Tom for mutants with altered fruit brightness. Our screen resulted in the isolation of 16 glossy and 8 dull mutants displaying changes in the amount and/or composition of wax and cutin, cuticle thickness, and surface aspect of the fruit as characterized by optical and environmental scanning electron microscopy. The main conclusions on the relationships between fruit brightness and cuticle features were as follows: (1) screening for fruit brightness is an effective way to identify tomato cuticle mutants; (2) fruit brightness is independent from wax load variations; (3) glossy mutants show either reduced or increased cutin load; and (4) dull mutants display alterations in epidermal cell number and shape. Cuticle composition analyses further allowed the identification of groups of mutants displaying remarkable cuticle changes, such as mutants with increased dicarboxylic acids in cutin. Using genetic mapping of a strong cutin-deficient mutation, we discovered a novel hypomorphic allele of GDSL lipase carrying a splice junction mutation, thus highlighting the potential of tomato brightness mutants for advancing our understanding of cuticle formation in plants.

Highlights

The cuticle is a protective layer synthesized by epidermal cells of the plants and consisting of cutin covered and filled by waxes
Availability of the Arabidopsis (Arabidopsis thaliana) genome sequence, high-throughput gene expression analysis tools, and mutant collections enabled deciphering the biosynthetic pathways and transport networks involved in cutin, suberin, and wax biosynthesis (Pollard et al, 2008; Li-Beisson et al, 2009; Beisson et al, 2012; Yeats and Rose, 2013)
Fatty acids are transported to the cytoplasm where they undergo a series of modifications, including the activation to CoA thioesters by long chain acyl-CoA synthetases, oxidation by cytochrome P450 (CYP)–dependent fatty acid oxidases, and esterification to glycerol-based acceptors by glycerol-3-phosphate acyl transferases to produce acyl-glycerols (Pollard et al, 2008; Li-Beisson et al, 2009)

Summary

Introduction

The cuticle is a protective layer synthesized by epidermal cells of the plants and consisting of cutin covered and filled by waxes. The plasma membrane ATP-binding cassette transporters have been implicated in the transport of both wax and cutin to the apoplast, whereas lipid transfer proteins very likely contribute to the transport of cutin monomers through the cell wall to the cutin layer (Yeats and Rose, 2013). The same gene families as for cutin likely contribute to suberin formation (Franke et al, 2012), which includes specific steps such as fatty acid elongation involving b-keto acyl-CoA synthases and primary alcohol synthesis implicating fatty acyl reductases (Domergue et al, 2010). Export of wax through plasma membrane occurs via ATP-binding cassette transporters and glycosylphosphotidylinositol-anchored lipid transfer proteins (Kunst and Samuels, 2009; Yeats and Rose, 2013)

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Conclusion