# Color Mutations Alter the Biochemical Composition in the San Marzano Tomato Fruit
## 1 Introduction  
In tomato (_Solanum lycopersicum_ L.), fruit color is one of the most important traits affecting consumer liking, and it is the result of combined effect of carotenoids, flavonoids and eventually chlorophylls. The red color of ripe fruit comes from the accumulation of all-trans-lycopene; mutants affected in the carotenoid pathway have an altered carotenoid composition, resulting in different fruit colors [1; 2]. Besides carotenoids, flavonoids play a role in determining the color of tomato fruit, particularly at the epidermal level [3]. One of the most abundant flavonoids in tomato fruit peel is the yellow-colored naringenin chalcone, often preceding and paralleling the production of lycopene in the pericarp [4]. Lastly, chlorophylls can eventually have a role in defining the color of the fruit; although they are normally degraded during ripening, \"stay green\" (SGR) mutants exist, that maintainimportant chlorophyll levels in the ripe fruit. Color variations do not only change fruit pigmentation, but they also affect the entire set of tomato fruit attributes, adversely or positively impacting the organoleptic and nutritional properties. Indeed, ripening involves a number of physiological processes ranging from the chlorophyll breakdown to the consecutive carotenoid accumulation, but also of other compounds belonging to the secondary metabolism, which play functional roles in plants [5], and have a potential in preventing diseases and promoting health in animals and humans [6; 7]. Among them, acids, docochromanols, quinones, fatty acids, sugars and polyols, as well as glycoalkaloids vary during ripening, thus modifying the nutritional value and the antioxidant activity of the fruit [8]. Three tomato mutants, _yellow flesh_ (\(r\)), _colorless fruit epidermis_ (\(y\)) and _green flesh_ (\(gf\)), which are representative of the main classes of color pigments, were chosen to be studied at metabolite level, with the aim of assessing the impact of these mutations on the fruit metabolome with emphasis on compounds that co-participate in defining fruit qualities. Yellow-fruited tomatoes have been documented since the first introduction in Europe [4; 9]. The yellow color is due to the \(r\) mutation, represented by loss-of-function alleles of phytoene synthase 1 (_Psyl_1; _Psyl_1 catalyzes the first rate-limiting step in the carotenoid pathway, the condensation of two molecules of geranylgeranyl diphosphate in phytoene [10]), which results in the inhibition of the whole carotenoid biosynthesis [11]. Recently, \(r\) tomatoes have been meeting with an increasing success, for the color novelty and the peculiar organoleptic qualities [12]. The \(y\) fruit mutant was originally described as a monogenic recessive variant leading to the formation of a colorless fruit peel [13]. The mutation, mapped on the short arm of Chr1 [14], involves the _SIMYB12_ transcription factor, causing the lack of naringenin chalcone, one of the major flavonoids in tomato fruit peel, which gives the yellow color and has been proposed to influence the characteristics and function of the cuticular layer [15; 16]. The pink \(y\)-type fruit mutation has been identified in numerous cultivated varieties that are highly consumed in Asian countries. Fruits of \(gf\) tomato mutant were described for their characteristic muddy brown color, resulting from the accumulation of lycopene coupled with the heterochronic presence of chlorophyll in the ripen fruit due to a lack of chlorophyll degradation [17]. In \(S\). _Iyocpersicum_, the \(Gf\) locus maps on the long arm of Chr8. Further studies indicated that \(gf\) is a member of the SGR gene family, _SISGR1_, a Mg-decheletase gene needed for chlorophyll catabolism [18; 19]. Nowadays, many cultivated tomatoes, heirloom varieties but also modern hybrids, exhibiting the \(gf\) phenotype are commercially available; indeed, these varieties are appreciated and have been reported to be superior for taste-related compounds [20; 21].