“Stay-green” crop phenotypes have been shown to impact drought tolerance and nutritional content of several crops. We aimed to genetically describe and functionally dissect the particular stay-green phenomenon found in chickpeas with a green cotyledon color of mature dry seed and investigate its potential use for improvement of chickpea environmental adaptations and nutritional value. We examined 40 stay-green accessions and a set of 29 BC2F4-5 stay-green introgression lines using a stay-green donor parent ICC 16340 and two Indian elite cultivars (KAK2, JGK1) as recurrent parents. Genetic studies of segregating populations indicated that the green cotyledon trait is controlled by a single recessive gene that is invariantly associated with the delayed degreening (extended chlorophyll retention). We found that the chickpea ortholog of Mendel’s I locus of garden pea, encoding a SGR protein as very likely to underlie the persistently green cotyledon color phenotype of chickpea. Further sequence characterization of this chickpea ortholog CaStGR1 (CaStGR1, for carietinum stay-green gene 1) revealed the presence of five different molecular variants (alleles), each of which is likely a loss-of-function of the chickpea protein (CaStGR1) involved in chlorophyll catabolism. We tested the wild type and green cotyledon lines for components of adaptations to dry environments and traits linked to agronomic performance in different experimental systems and different levels of water availability. We found that the plant processes linked to disrupted CaStGR1 gene did not functionality affect transpiration efficiency or water usage. Photosynthetic pigments in grains, including provitaminogenic carotenoids important for human nutrition, were 2–3-fold higher in the stay-green type. Agronomic performance did not appear to be correlated with the presence/absence of the stay-green allele. We conclude that allelic variation in chickpea CaStGR1 does not compromise traits linked to environmental adaptation and agronomic performance, and is a promising genetic technology for biofortification of provitaminogenic carotenoids in chickpea.
AbstractIntroductionThe availability of β-carotene from provitamin A rich foods in order to improve the provision of vitamin A in humans through food-based approaches is an important factor in mitigating micronutrient deficiencies. However, the extent of intestinal absorption (and subsequent availability of carotenoids to target tissues) is dependent on meal preparation, components of the meal and other intrinsic factors during gastro-intestinal (GI) digestion. Gastric emptying (GE), dictated by the caloric value of a meal, has been suggested as a critical component in determining β-carotene absorption. Indeed, dietary intake of high energy meals may just unravel the underlying factors associated with low uptake of dietary carotenoids during digestion. While several studies have reported the uptake of β-carotene as an individual pure compound under different digestive conditions(1), very few studies have assessed the effects of dietary carotenoids embedded in an energy dense meal, as would normally be consumed, on GI transit time and subsequent nutrient release.Materials and MethodsIn this study, we investigated the role of meal composition, particularly its caloric value, in modulating gastric emptying and thus the absorption of β-carotene. A step-by-step in vitro semi-dynamic model that simulates adult gastric digestion(2) was used on a prepared standard meal whose caloric value was estimated based on the Atwater system as described elsewhere with the assumption that the caloric density of the meal will assume a linear GE rate of 2kcal/min.ResultsPreliminary results indicate that, short transit times of 40 minutes, mimicking early GE, have the highest concentration (3.84 ± 0.014; Mean SD) and therefore, highest bioaccessibility (55.7%) compared to the longer transit time of 160 minutes (0.81 ± 0.002; Mean SD) and (11.8%) for β-carotene concentration and bioaccessibility from a standard meal, respectively.DiscussionThe results suggest that gastric behaviour of the food determines the kinetics of bioaccessibility that may not result in low β-carotene release and ultimately low bioaccessibility from the embedded matrix.
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