Pleiotropic Phenotypes of the sticky peel Mutant Provide New Insight into the Role of CUTIN DEFICIENT2 in Epidermal Cell Function in Tomato    

Abstract

Plant epidermal cells have evolved specialist functions associated with adaptation to stress. These include the synthesis and deposition of specialized metabolites such as waxes and cutin together with flavonoids and anthocyanins, which have important roles in providing a barrier to water loss and protection against UV radiation, respectively. Characterization of the sticky peel (pe) mutant of tomato (Solanum lycopersicum) revealed several phenotypes indicative of a defect in epidermal cell function, including reduced anthocyanin accumulation, a lower density of glandular trichomes, and an associated reduction in trichome-derived terpenes. In addition, pe mutant fruit are glossy and peels have increased elasticity due to a severe reduction in cutin biosynthesis and altered wax deposition. Leaves of the pe mutant are also cutin deficient and the epicuticular waxes contain a lower proportion of long-chain alkanes. Direct measurements of transpiration, together with chlorophyll-leaching assays, indicate increased cuticular permeability of pe leaves. Genetic mapping revealed that the pe locus represents a new allele of CUTIN DEFICIENT2 (CD2), a member of the class IV homeodomain-leucine zipper gene family, previously only associated with cutin deficiency in tomato fruit. CD2 is preferentially expressed in epidermal cells of tomato stems and is a homolog of Arabidopsis (Arabidopsis thaliana) ANTHOCYANINLESS2 (ANL2). Analysis of cuticle composition in leaves of anl2 revealed that cutin accumulates to approximately 60% of the levels observed in wild-type Arabidopsis. Together, these data provide new insight into the role of CD2 and ANL2 in regulating diverse metabolic pathways and in particular, those associated with epidermal cells.

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

“…Our study clearly shows that although all selected brightness mutants displayed cuticle alterations, the glossy/dull fruit trait is not due to one single alteration. Recent studies of tomato mutants and transgenic lines established that increased fruit glossiness was associated with cutin deficiency Girard et al, 2012;Nadakuduti et al, 2012;Shi et al, 2013). We indeed confirmed this relationship for several mutants (Fig.…”

“…fruit growth, visual aspect, cracking, water loss, resistance to pathogens, and postharvest shelf-life) are highly dependent on fruit cuticle (Bargel and Neinhuis, 2005;Saladié et al, 2007;Matas et al, 2009;Domínguez et al, 2011;Parsons et al, 2012). An increasing number of studies highlight the possibilities offered by tomato for analyzing cuticle architecture, mechanical properties, and permeability (López-Casado et al, 2007;Saladié et al, 2007;MintzOron et al, 2008;Buda et al, 2009;Isaacson et al, 2009;Wang et al, 2011) and for discovering genes contributing to cuticle synthesis and regulation (Hovav et al, 2007;Mintz-Oron et al, 2008;Girard et al, 2012;Nadakuduti et al, 2012;Yeats et al, 2012b;Shi et al, 2013). Nevertheless, to further our understanding of the relationships between cuticle composition and architecture and cuticle properties and performance in plants, new tomato cuticle mutants are highly needed (Domínguez et al, 2011).…”

“…By contrast, up to five glossy mutants displayed significant increases in cutin load, which ranged from approximately 722.9 mg/cm 2 (P4B6) to 1175.5 mg/cm 2 (P17F12). As in other tomato cultivars described to date (Mintz-Oron et al, 2008;Girard et al, 2012;Nadakuduti et al, 2012), cutin monomers are mostly made up of polyhydroxy fatty acids (65%, with 9,16-dihydroxy-palmitic acid representing 95% of the total) and v-hydroxy fatty acids (11%), and in lesser amounts by fatty acids (approximately6%) and dicarboxylic acids (approximately 5%) (Table II). Whereas changes in cutin load were usually paralleled by similar changes in the various classes of cutin monomers, several glossy mutants displayed remarkable and specific patterns of accumulation of cutin monomers.…”

“…Using this strategy, new cuticle-related genes involved in cuticle regulation (the cd2 HD-ZIP IV mutant; Isaacson et al, 2009), cutin monomer biosynthesis (the cyp86A9 mutant; Shi et al, 2013), and cutin polymerization (the cutin synthase mutant; Yeats et al, 2012b) were recently uncovered in tomato EMS mutant collections. However, when considering the large number of candidate genes involved in the regulation, synthesis, and transport processes necessary for cuticle formation (Matas et al, 2011;Yeats and Rose, 2013), very few tomato cuticle mutants have been described to date (Kimbara et al, 2012;Nadakuduti et al, 2012;Shi et al, 2013).…”

“…We further focused on cutin mutants because cutin load is possibly the major factor controlling fruit brightness in tomato (Girard et al, 2012;Nadakuduti et al, 2012;Yeats et al, 2012b), and the possible effects of wax changes on glossiness have already been well described in Arabidopsis (Chen et al, 2003;Aharoni et al, 2004;Bourdenx et al, 2011). One way to identify the possible origin of the mutation is to combine the wealth of information now available on cuticle biosynthesis and regulation with the data on fruit surface chemistry.…”