Carotenoid biosynthesis genes provide evidence of geographical subdivision and extensive linkage disequilibrium in the carrot

According to the history of the cultivated carrot, root colour can be considered as a structural factor of carrot germplasm. Therefore, molecular variations of carotenoid biosynthesis genes, these being involved in colour traits, represent a good putative source of polymorphism related to diversity structure. Seven candidate genes involved in the carotenoid biosynthesis pathway have been analysed from a sample of 48 individual plants, each one from a different cultivar of carrot (Daucus carota L. ssp. sativus). The cultivars were chosen to represent a large diversity and a wide range of root colour. A high single nucleotide polymorphism (SNP) frequency of 1 SNP per 22 bp (mean π sil = 0.020) was found on average within these genes. The analysis of genetic structure from carotenoid biosynthesis gene sequences and 17 putatively neutral microsatellites showed moderate genetic differentiation between cultivars originating from the West and the East (F ST = 0.072), this being consistent with breeding history, but not previously evidenced by molecular tools. Surprisingly, carotenoid biosynthesis genes did not exhibit decay of LD (mean r 2  = 0.635) within the 700–1,000 bp analysed, even though a fast decay level of LD is expected in outcrossing species. The high level of intralocus LD found for carotenoid biosynthesis genes implies that candidate-gene association mapping for carrot root colour should be useful to validate gene function, but may be unable to identify precisely the causative variations involved in trait determinism. Finally this study affords the first molecular evidence of a genetic structure in cultivated carrot germplasm related to phylogeography

Carotenoid gene expression explains the difference of carotenoid accumulation in carrot root tissues

The carrot root is well divided into two different tissues separated by vascular cambium: the secondary phloem and xylem. The equilibrium between these two tissues represents an important issue for carrot quality, but the knowledge about the respective carotenoid accumulation is sparse. The aim of this work was (i) to investigate if variation in carotenoid biosynthesis gene expression could explain differences in carotenoid content in phloem and xylem tissues and (ii) to investigate if this regulation is differentially modulated in the respective tissues by water-restricted growing conditions. In this work, five carrot genotypes contrasting by their root color were studied in control and water-restricted conditions. Carotenoid content and the relative expression of 13 genes along the carotenoid biosynthesis pathway were measured in the respective tissues. Results showed that in orange genotypes and the purple one, carotenoid content was higher in phloem compared to xylem. For the red one, no differences were observed. Moreover, in control condition, variations in gene expression explained the different carotenoid accumulations in both tissues, while in water-restricted condition, no clear association between gene expression pattern and variations in carotenoid content could be detected except in orange-rooted genotypes. This work shows that the structural aspect of carrot root is more important for carotenoid accumulation in relation with gene expression levels than the consequences of expression changes upon water restriction

Expression of carotenoid biosynthesis genes during carrot root development

Carotenogenesis has been extensively studied in fruits and flower petals. Transcriptional regulation is thought to be the major factor in carotenoid accumulation in these organs. However, little is known about regulation in root organs. The root carotenoid content of carrot germplasm varies widely. The present study was conducted to investigate transcriptional regulation of carotenoid biosynthesis genes in relation to carotenoid accumulation during early carrot root development and up to 3 months after sowing. HPLC carotenoid content analysis and quantitative RT-PCR were compared to quantify the expression of eight genes encoding carotenoid biosynthesis enzymes during the development of white, yellow, orange, and red carrot roots. The genes chosen encode phytoene synthase (PSY1 and PSY2), phytoene desaturase (PDS), ζ-carotene desaturase (ZDS1 and ZDS2), lycopene ε-cyclase (LCYE), lycopene β-cyclase (LCYB1), and zeaxanthin epoxidase (ZEP). All eight genes were expressed in the white cultivar even though it did not contain carotenoids. By contrast with fruit maturation, the expression of carotenogenic genes began during the early stages of development and then progressively increased for most of these genes during root development as the total carotenoid level increased in coloured carrots. The high expression of genes encoding LCYE and ZDS noted in yellow and red cultivars, respectively, might be consistent with the accumulation of lutein and lycopene, respectively. The results showed that the accumulation of total carotenoids during development and the accumulation of major carotenoids in the red and yellow cultivars might partially be explained by the transcriptional level of genes directing the carotenoid biosynthesis pathway

The pattern of peptides released from dairy and egg proteins is highly dependent on the simulated digestion scenario

Evaluating the gastrointestinal (GI) fate of proteins is part of the assessment to determine whether proteins are safe to consume. In vitro digestion tests are often used for screening purposes in the evaluation of potential allergenicity. However, the current pepsin resistant test used by the European Food Safety Authority, only corresponds to fasted gastric conditions representative of a late phase adult stomach. In addition, these tests are performed on isolated proteins and the effect of the food matrix and processing are not systematically considered. The aim of this research is to compare three different static in vitro GI scenarios that are physiologically relevant. Namely, an infant, early phase (fed state) adult and late phase (fasted state) adult model. These protocols are applied to well-characterised isolated dairy (β-lactoglobulin and β-casein) and egg (lysozyme and ovalbumin) proteins and the impact of food matrix/processing on their proteolysis is also investigated. A combination of SDS-PAGE, LC-MS/MS and spectrometric assay was used for the evaluation of the proteolysis. Results highlight differences across the three GI scenarios whether on isolated proteins or within food matrices. The infant model led to incomplete digestion, leaving intact egg proteins, either isolated or in the food matrix, and intact β-lactoglobulin in the milk. In addition, peptides greater than 9 amino acids were found throughout the intestinal phase for all proteins studied, regardless of the scenario. This reinforces the difficulty of linking protein digestibility to potential allergenicity because many other factors are involved that need further investigation

Genetic diversity and taxonomic aspects of wild carrot in France

If in France, genetic resources of cultivated carrot are well studied and preserved, the wild compartment of the species remains unknown and underutilized, while there are many populations of wild carrot on the French territory. Several collecting missions were undertaken from 2009 to 2013 to identify and collect populations, particularly in coastal areas, in continental France and Corsica. More than a hundred populations were collected, with a good distribution throughout the territory, and eleven taxa were identified. The status of these taxa is variable, with some very common and others underrepresented or specific to a given area. Morphological and molecular studies are developed in order to improve the knowledge of taxonomy and diversity. The study conducted with microsatellite markers showed a high genetic diversity at the intra-and inter-populations levels. The overall results show that the Mediterranean coast and Corsica exhibit a particularly high diversity. The work confirms the specific interest of some populations and the taxonomic separation into 2 subgroups carota and gummifer in Daucus carota L. This study will allow developing a strategy for management of genetic resources and their valorisation in breeding