Involvement of ethylene in color changes and carotenoid biosynthesis in loquat fruit (Eriobotrya japonica Lindl. cv. Algerie)
Introduction
Loquat (Eriobotrya japonica L.) belongs to the Rosaceae family, is native of Southern China and is currently cultivated in more than 20 countries, being China and Spain the main producers (Calabrese, 2006). Ripening of loquat fruits has been classified as non-climacteric with a virtual absence of a rise in the respiration rate and autocatalytic ethylene production (Jiang et al., 2011; Pech et al., 2012; Reig et al., 2016). Furthermore, the transcriptional regulation of ethylene biosynthetic and perception genes reinforces the notion of a non-climacteric ripening behavior (Alós et al., 2017). However, several studies in loquat have revealed the involvement of ethylene in some ripening-related events or during storage, such as accumulation of sugars, the reduction of acids, flesh browning, polygalactoronase (PG) activity, lignin accumulation and the appearance of chilling injury lesions (Cai et al., 2006; Wang et al., 2010; Liguori et al., 2015). In addition, experiments involving the application of ethylene or 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, in loquat fruits revealed that ethylene seems to be required to sustain the expression of certain genes of its own biosynthesis (Alós et al., 2017).
External color is one of the main parameters of fruit quality and in loquat has been established as the main determinant for the harvest date (Cautín et al., 2006). Depending on the coloration of the flesh at mature stage, loquat fruits can be divided into two types: the white- and the red/orange-fleshed cultivars. The distinctive coloration of the fruit of the different varieties is due to the differential accumulation of specific carotenoids. The carotenoid biosynthetic pathway is well stablished in some fleshy fruits and the main metabolic steps have been characterized and extensively studied (Lado et al., 2016). Hence, carotenoids are formed from the 2-methyl-erythritol-phosphate (MEP) pathway which generates geranylgeranyl diphosphate (GGPP) that is then used to synthesize phytoene via phytoene synthase (PSY), the first committed step in carotenogenesis (Fig. 1). Subsequently, a series of desaturation and isomerization reactions catalyzed by phytoene desaturase (PDS), ζ-carotene desaturase (ZDS), ζ-carotene isomerase (ZISO), and carotenoid isomerase (CRTISO), lead to the formation of lycopene, the red-colored carotenoid. Lycopene β-cyclase (LCYB) and lycopene ε-cyclase (LCYE) together synthesize α-carotene or alternatively, a lycopene β-cyclase (LCYB) or a chromoplast-specific lycopene β-cyclase (CYCB) (Ronen et al., 2000; Alquézar et al., 2009) synthesize β-carotene (Fig. 1). The cyclization of lycopene to produce α-carotene or β-carotene leads to the bifurcation of the pathway into the α- and the β-branch, respectively. Then, the hydroxylation of α-carotene and β- carotene by β- and ε-carotene hydroxylases (BCH, CYP97 A and B) generate yellow xanthophylls of lutein in the α-branch and zeaxanthin in the β-branch. The epoxidation and de-epoxidation of zeaxanthin by zeaxanthin epoxidase (ZEP) and violaxanthin de-epoxidase (VDE) constitute the so-called xanthophyll cycle. The conversion of violaxanthin into neoxanthin by neoxanthin synthase (NSY) concludes the core biosynthetic pathway (reviewed in Giuliano, 2017; Sun et al., 2017, Fig. 1).
The genetic and transcriptional regulation of the carotenoid biosynthetic pathway in fruits of loquat genotypes with different carotenoid accumulation patterns has been recently addressed. Studies on loquat cv. Luoyangqin (LYQ) and cv. Baisha (BS) with orange- and white-fleshed fruits, respectively, revealed significant differences in carotenoid content and composition in peel and pulp tissues between both cultivars associated with the differential expression of the carotenoid biosynthetic genes: PSY1, CYCB and BCH (Fu et al., 2012, 2014). Recently, Hadjipieri et al. (2017) analyzed the carotenoid composition and the expression of several carotenoid biosynthetic genes during on-tree maturation of the red/orange-fleshed cv. Obusa. During maturation, lutein content in the peel decreased progressively and increased the concentration of β-carotene, while β-cryptoxanthin and β-carotene were the main carotenoids in the pulp. Analysis of gene expression in peel and pulp of fruits at six developmental/maturation stages revealed that these changes in carotenoid content were linked to the coordinated upregulation of CYCB and the repression of LCYB and LCYE genes (Hadjipieri et al., 2017). Therefore, the shifting from the β,ε to β,β branch of the carotenoid biosynthesis pathway and the hydroxylation of β−carotene appear to be key steps in the regulation of carotenoid accumulation in loquat fruits.
Carotenoid synthesis and accumulation in fruits are influenced by different developmental and environmental factors (Lado et al., 2016). In climacteric fruits, ethylene plays a key role in the regulation of fruit coloration and carotenoid biosynthesis (Grierson, 2013). In non-climacteric fruits, however, the absence of an upsurge of ethylene production during maturation does not discard the involvement of the hormone in the regulation of fruit coloration. Indeed, in Citrus fruit, in which application of ethylene is commercial used worldwide to degreen early harvested cultivars (Porat, 2008), it has been suggested that ethylene action is required for the expression of carotenoids biosynthesis genes and peel coloration (Rodrigo and Zacarías, 2007; Rodrigo et al., 2013). Moreover, inhibition of ethylene perception by postharvest application of 1-methylcyclopropene (1-MCP), an inhibitor of the ethylene action, is a valuable experimental tool to clarify the role of endogenous ethylene on several ripening-related events, including fruit pigmentation (Watkins, 2008; Li et al., 2016). In particular, application of 1-MCP to loquat has been shown to reduce the incidence of postharvest disorders as chilling injury (internal browning and leatheriness) and decay (Pareek et al., 2013; Li et al., 2016) and also to delay ripening (Liguori et al., 2015). Together, these observations indicate that ethylene may be involved in specific aspects of the postharvest performance of loquat fruits. However, the involvement of the hormone in the regulation of fruit coloration and carotenoid biosynthetic in this fruit, and whether 1-MCP may be commercially used to manipulate fruit coloration, have not been elucidated. Hence, in the present study we have addressed two objectives: 1) to analyze carotenoid content and expression of key biosynthetic genes in peel and pulp of loquat (cv. Algerie) fruit during on-tree maturation, and 2) to investigate the effects of ethylene and 1-MCP during postharvest on color changes and carotenoid biosynthesis in both peel and pulp tissue of loquat fruits cv. Algerie, the predominant cultivar in Spain. Overall, the data suggest that, despite the non-climacteric ripening of loquat, coloration and carotenoid accumulation can be manipulated by modulation of ethylene action, most likely throughout transcriptional changes in carotenoid biosynthetic genes, but the effect appears to be tissue- and maturation stage-specific.
Section snippets
Plant material and treatments
Fruits were harvested from 6 adult (20–25 years old) trees of loquat cv. Algerie (Eriobotrya japonica Lindl.) grown in a commercial orchard in Callosa d’En Sarriá, (Alicante, Spain), the main area of loquat production in Spain. This cultivar was selected by the excellent quality of its fruit and because it is the one with highest production in the Mediterranean basin. Trees were budded onto loquat seedling rootstocks, grown in a loamy-clay soil, pH 7.5–8.0, planted 4 × 4 m apart, with drip
Evolution of color index and pigment concentrations during on-tree loquat fruit maturation
Color index (CI) data showed that fruit peel was greener than the pulp at BK stage (-0.33 and -0.13, respectively, Fig. 2A and B). As fruit maturation progressed, external pigmentation and CI increased, being higher in the peel than in the pulp (Fig. 2A and B). Total carotenoid and chlorophyll content was also measured at these maturation stages and indicated a higher pigment concentration in the peel than in the pulp. Total carotenoids in the peel were almost the same in Y and BK fruits, and
Discussion
In loquat, changes in coloration, i.e. in carotenoid content and composition in peel and pulp, during fruit maturation, are mainly due to transcriptional regulation of carotenoid biosynthetic genes (De Faria et al., 2009; Fu et al., 2014; Hadjipieri et al., 2017). Despite recent evidence that indicate a non-climacteric ripening behavior of loquat fruit, other results also suggest that several ripening-related processes could be potentially manipulated by either exogenous ethylene or by
Acknowledgements
Dr. E. Alos was recipient a post-doctoral contract JAE-Doc-CSIC (Fondo Social Europeo). The financial support of the research grants FP7-PEOPLE-2011-CIG-2011-303652 (Marie Curie Actions, European Union), AGL-2015-70218 (Ministerio Economía y Competitividad, Spain), GV/2012/036 (GeneralitatValenciana, Spain) and PROMETEO-II 2014/27 (Generalitat Valenciana) are gratefully acknowledged. MJR and LZ are members of Eurocaroten (COST_Action CA15136) and CaRed (Spanish Carotenoid Network,
References (43)
- et al.
Ethylene biosynthesis and perception during ripening of loquat fruit (Eriobotrya japonica Lindl.)
J. Plant Physiol.
(2017) - et al.
Effect of 1-MCP on postharvest quality of loquat fruit
Postharvest Biol. Technol.
(2006) - et al.
Stimulation of coloration and carotenoid biosynthesis during postharvest storage of ‘Navelina’ orange fruit at 12 °C
Postharvest Biol. Technol.
(2012) - et al.
The high content of β-carotene present in orange-pulp fruits of Carica papayaL. is not correlated with a high expression of the CpLCY-β2 gene
Food Res. Int.
(2017) - et al.
Cultivar influence on carotenoid composition of loquats from Brazil
J. Food Anal.
(2009) Provitamin A biofortification of crop plants: a gold rush with many miners
Curr. Opin. Biotechnol.
(2017)- et al.
Ethylene biosynthesis and expression of related genes in loquat fruit at different developmental and ripening stages
Sci. Hort.
(2011) - et al.
Effects of the ethylene inhibitor 1-methylcyclopropene on postharvest quality of non-climacteric fruit crops
Postharvest Biol. Technol.
(2016) - et al.
A comprehensive review on the colorless carotenoids phytoene and phytofluene
Arch. Biochem. Biophys.
(2015) - et al.
Biochemical bases and molecular regulation of pigmentation in the peel of Citrus fruit
Sci. Hortic.
(2013)
Effect of postharvest ethylene treatment oncarotenoid accumulation and the expression of carotenoid biosynthetic genes in the flavedo of orange (Citrus sinensis L. Osbeck) fruit
Postharvest Biol. Technol.
A global perspective on carotenoids: metabolism, biotechnology, and benefits for nutrition and health
Progress Lipid Res.
Cloning and functional analysis of the β-carotene hydroxylase of Arabidopsis thaliana
J. Biol. Chem.
Molecular and functional characterization of a novel chromoplast-specific lycopene β-cyclase from Citrus and its relation to lycopene accumulation
J. Exp. Bot.
U/V visible spectroscopy
The MIQe guidelines: minimum information for publication of quantitative real-time PCR experiments
Clin. Chem.
Origen de la especie
Changes in color-related compounds in tomato fruit exocarp and mesocarp during ripening using HPLC-APcI (+)-mass spectrometry
J. Food Sci. Technol.
Técnicas de cultivo. In El cultivo del níspero japonés
Involvement of multiple phytoene synthase genes in tissue- and cultivar-specific accumulation of carotenoids in loquat
J. Exp. Bot.
Plastid structure and carotenogenic gene expression in red-and white-fleshed loquat (Eriobotrya japonica) fruits
J. Exp. Bot.
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