Abstract
Endive (Cichorium endivia L.), a vegetable consumed as fresh or packaged salads, is mostly cultivated outdoors and known to be sensitive to waterlogging in terms of yield and quality. Phenotypic, metabolic and transcriptomic analyses were used to study variations in curly- (‘Domari’, ‘Myrna’) and smooth-leafed (‘Flester’, ‘Confiance’) cultivars grown in short-term waterlog due to rainfall excess before harvest. After recording loss of head weights in all cultivars (6-35%), which was minimal in ‘Flester’, NMR untargeted profiling revealed variations as influenced by genotype, environment and interactions, and included drop of total carbohydrates (6–50%) and polyols (3–37%), gain of organic acids (2–30%) and phenylpropanoids (98–560%), and cultivar-specific fluctuations of amino acids (−37 to +15%). The analysis of differentially expressed genes showed GO term enrichment consistent with waterlog stress and included the carbohydrate metabolic process. The loss of sucrose, kestose and inulin recurred in all cultivars and the sucrose-inulin route was investigated by covering over 50 genes of sucrose branch and key inulin synthesis (fructosyltransferases) and catabolism (fructan exohydrolases) genes. The lowered expression of a sucrose gene subset together with that of SUCROSE:SUCROSE-1-FRUCTOSYLTRANSFERASE (1-SST) may have accounted for sucrose and kestose contents drop in the leaves of waterlogged plants. Two anti-correlated modules harbouring candidate hub-genes, including 1-SST, were identified by weighted gene correlation network analysis, and proposed to control positively and negatively kestose levels. In silico analysis further pointed at transcription factors of GATA, DOF, WRKY types as putative regulators of 1-SST.
Highlights
Curly- and smooth- leafed endives (Cichorium endivia var. crispum and var. latifolium) are consumed worldwide as fresh or minimally processed salads that are sources of healthy nutrients[1] and good-profit greens in the export of EU major producers such as Spain, France and Italy (TrendEconomy, http://trendeconomy.com)
It is speculated that the different sensitivity of endives might rely on the root system made of abundant fibrous roots prevailing over a small taproot in endive, while the opposite occurs in industrial chicory
Effects of genotype (G), year (Y) and interaction (G×Y) by two-way ANOVA are below each panel. *, **, *** = significant at P ≤ 0.05, 0.01 and 0.001 respectively; ns non-significant. d principal component analysis of leaf metabolites (PCA) biplot shows the spatial distribution of 30 hydrosoluble compounds in curly Domari and Myrna (D, M) and smooth Confiance and Flester (C, F) cultivated in Lazio in 2011 and 2012
Summary
Curly- and smooth- leafed endives (Cichorium endivia var. crispum and var. latifolium) are consumed worldwide as fresh or minimally processed salads that are sources of healthy nutrients[1] and good-profit greens in the export of EU major producers such as Spain, France and Italy (TrendEconomy, http://trendeconomy.com). The Italian cultivation of endives (http://dati.istat.it/) occurs mostly in open field (97% of 8426 ha and yield of 1886738 q in 2019) in autumn-winter cycles because it is low input and cold-tolerant crop[2]. Oxygen deficiency directly affects the root while the shoot remains oxygenated, underground and aerial organs react differently with anatomical and metabolic modifications[4]. The waterlog impact on plant metabolism varies with severity, timing and duration of stress and with genotype tolerance[5]. Leaf responses include stomatal closure and non-stomatal metabolic alterations (e.g. oxidative stress) that lead to decreased CO2 incorporation and net photosynthesis drop, while the bleaching is recurrently associated with chlorophyll loss and senescence. Leaves of sensitive crops undergo stronger alteration in sugar, amino acids and TCA metabolism. Tolerant species, which are more efficient in carbohydrate utilization, the show raised levels of fumarate, γ-aminobutirric acid and alanine belonging to routes tailored to compensate anoxia damages[9]
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