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Browsing by Author "Rhodes, Davina, advisor"

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    Bridging the gap between biofortification and consumption: evaluating sorghum grain carotenoid degradation
    (Colorado State University. Libraries, 2023) Lepard, Ariel, author; Rhodes, Davina, advisor; Van Buiten, Charlene, committee member; Prenni, Jessica, committee member; Scanlin, Laurie, committee member
    Sorghum (Sorghum bicolor) is a major staple cereal crop consumed in sub-Saharan Africa and Southeast Asia, where some of the highest rates of vitamin A deficiency (VAD) are found. As with most cereals, sorghum has low concentrations of provitamin A carotenoids, which are converted to vitamin A in the body. Biofortification provides an opportunity to address VAD through the nutritional improvement of sorghum grain using a non-transgenic breeding approach to increase grain carotenoids. Though vitamin A biofortification in sorghum is possible, it is unknown if breeding for high carotenoids in the grain negatively affects carotenoid pathway functions in other tissues. Additionally, it is unknown if degradation during postharvest processing occurs to a significant degree in biofortified grain. To establish how breeding for high carotenoids in the grain affects the carotenoid pathway in other plant tissues, expression of ten genes in the carotenoid precursor, biosynthesis, or degradation pathways were evaluated in the grain, leaf, and root tissues. A correlation in the gene expression within the plant tissue, but not between the plant tissues, was found for most genes, which suggests that several of the carotenoid precursor, biosynthesis, and degradation genes are controlled by tissue-specific regulation. Correlation of carotenoid concentrations and gene expression was also found to be tissue specific, which further suggests tissue-specific regulation. The selection of genes with tissue-specific regulation for marker-assisted breeding reduces the chances of grain biofortification negatively affecting other tissues. Once carotenoids have been increased in the grain, it must be noted that vitamin A is not stable in most storage, processing, and cooking environments due to oxidative stress from light, heat, and oxygen. The degradation of the nutritional quality through post-harvest processing was evaluated by sampling carotenoid grain throughout harvest, drying, storage, processing, and cooking. Individual processing steps did not cause significant degradation but added up to significant degradation by the final cooking step, with ~39% of β-carotene loss. No significant difference between the loss in the different storage temperatures or cooking styles was seen. An increase in the target value from 4 μg β-carotene/g of sorghum to 5.6 μg/g will be needed to account for processing loss in order to provide 50% of the estimated average requirement (EAR) of vitamin A. Overall, both the information on tissue specific gene expression, and post-harvest degradation will further advance the development of carotenoid biofortified sorghum lines.
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    Characterizing controls of sorghum carotenoid bioaccessibility for vitamin A biofortification
    (Colorado State University. Libraries, 2024) McDowell, Rae, author; Rhodes, Davina, advisor; Morris, Geoff, committee member; Chaparro, Jacqueline, committee member
    Vitamin A deficiency is one of the leading causes of preventable blindness globally and can lead to decreased immune function and mortality. Sorghum bicolor is consumed in areas that are affected by vitamin A deficiency, where biofortification of sorghum may be a way to address these nutritional deficiencies. However, sorghum breeders do not know the target breeding value for provitamin A carotenoids or the best breeding strategy for carotenoid biofortification. Bioaccessibility—the amount of a nutrient available to be absorbed in the gut—can be reduced by a variety of factors, and needs to be determined in order to define a biologically relevant target value of provitamin A carotenoids. Additionally, genetic controls of grain bioaccessibility need to be determined in order to develop breeding tools. This research sought to develop biofortification breeding strategies by characterizing the environmental and genetic controls of carotenoid bioaccessibility through genomic mapping and multi-environment trials. We hypothesized that 1) genotype has a greater impact on variation in carotenoid bioaccessibility than genotype by environment interactions, and 2) carotenoid bioaccessibility is an oligogenic trait. To test these hypotheses, twelve sorghum genotypes were grown across three climates (semi-arid, humid-subtropical, and humid-continental) for two years. Results suggest there is a strong environmental and genotype by environment interaction in the regulation of bioaccessibility of sorghum carotenoids. One environmental factor that may contribute to variation in bioaccessibility is iron and zinc content, which was found to have a significant negative correlation with carotenoid bioaccessibility traits. Next, genome-wide association studies (GWAS) in a diverse population and linkage mapping in a F5.6 recombinant inbred family identified a handful of genes or regions underlying variation in carotenoid bioaccessibility and carotenoid content, supporting the hypothesis that there are oligogenic controls. GWAS revealed two significant marker trait associations (MTAs) underlying relative bioaccessibility of ɑ-cryptoxanthin and cis-β-carotene on chromosomes five and one respectively. Furthermore, in the inbred family, there were observations of transgressive segregation, in which a portion of the progeny exceeded parental means for both carotenoid content and bioaccessibility. Additionally, linkage analysis identified six unique regions for carotenoid content and three unique regions for carotenoid bioaccessibility, further supporting the oligogenic hypothesis for genetic architecture. Linkage analysis also revealed colocalization of regions between carotenoid content and carotenoid bioaccessibility, either suggesting co-regulation or linkage between traits. Interestingly, several a priori candidate genes in proximity to identified MTAs and linkage regions were broadly involved in carbohydrate, lipid, and carotenoid metabolism. These results will help refine the carotenoid biofortification target value and lead to the development of molecular breeding tools that can be used to increase carotenoid content and bioaccessibility, as well as to maintain favorable alleles, in sorghum breeding germplasm.
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    Development of a high-throughput phenotyping method for measuring sorghum carotenoids
    (Colorado State University. Libraries, 2024) Zapata Carvajal, Nelson David, author; Rhodes, Davina, advisor; Prenni, Jessica, committee member; Weir, Tiffany, committee member
    Vitamin A deficiency is the leading cause of preventable blindness in young children, and also leads to infertility and decreased immune function. Humans cannot synthesize vitamin A, so it must be consumed in the diet, either as preformed vitamin A or as provitamin carotenoid (PVACs) in plant foods. Access to PVACs is limited in sub-Saharan Africa where many diets are less diverse and primarily consist of cereals, such as sorghum, with intrinsically low concentrations of PVACs. Therefore, biofortification breeding efforts aim to increase PVACs to biologically relevant levels to reduce global vitamin A deficiency. In order to select and breed high carotenoid varieties, thousands of progeny in a breeding program must be phenotyped. High-performance liquid chromatography (HPLC) is the gold standard carotenoid phenotyping method; however, it is expensive and time-consuming, making it impractical for large-scale screening. We hypothesized that a high-throughput phenotyping (HTP) method using UV-VIS spectrophotometry can identify high carotenoid sorghum lines for selection during breeding. In this study, a simple and rapid method for carotenoid extraction and UV-VIS spectrophotometric detection in a 96-well plate format was developed and validated. To develop the HTP method, we measured 60 samples using both HPLC and UV-VIS, identifying a strong correlation (R2=0.62, p-value<4.51x10-14) between total carotenoid concentrations measured with the HTP method and the gold standard HPLC method. To validate the HTP method, we measured carotenoids in 249 lines in a biparental breeding family, using both HPLC and UV-VIS, and again identified a strong correlation (R2=0.61, p-value<2.2x10-16). We also compared the predictability of the UV-VIS method to that of a simple visual inspection of grain color and found that the UV-VIS method performed significantly better. This promising HTP method will enable rapid screening of a large number of samples, helping breeders more efficiently make selections for carotenoid biofortification.
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    Development of molecular breeding resources for increased pro-vitamin A carotenoids in sorghum grain
    (Colorado State University. Libraries, 2022) Cruet-Burgos, Clara María, author; Rhodes, Davina, advisor; Mason, Esten, committee member; Prenni, Jessica, committee member; Pressoir, Gael, committee member
    Vitamin A deficiency (VAD) affects millions of people in countries in Africa and South-East Asia, contributing to decreased immune response and increased morbidity and mortality from common infections. Sorghum [Sorghum bicolor L. (Moench)] is a staple cereal crop in these regions, thus, sorghum carotenoid biofortification is a potential method to improve the vitamin A status of these communities. The overall aim of this research was to determine the feasibility of biofortification breeding for sorghum grain carotenoids, and to develop genomic tools to assist in molecular breeding. Global sorghum germplasm collections were evaluated for pro-vitamin A carotenoids, and concentrations were found to be below target values. Due to the low number of accessions with above average pro-vitamin A content, the genetic diversity of the high carotenoid lines in the global germplasm was assessed. High carotenoid accessions were found to be highly related, hence, to increase genetic diversity for breeding, a genomic prediction model was used to identify additional germplasm with potentially high concentrations of pro-vitamin A carotenoids. Through a genome-wide association study, it was confirmed that carotenoid variation in sorghum grain is oligogenic, but there was also evidence of a polygenic component. Therefore both marker-assisted selection (MAS) and genomic selection (GS) may be effective in accelerating breeding efforts. KASP markers in linkage with genomic regions associated with carotenoid concentrations were developed and validated in six F2:3 populations. Two markers in the intronic region of the carotenoid pathway β-OH gene were identified as good candidates to use for MAS due to their predictive ability. A marker inside the coding sequence of the carotenoid pathway ZEP gene was also identified as a good marker for MAS. An RNA-seq experiment identified additional genes in the MEP, carotenoid biosynthesis and carotenoid degradation pathways that could be used for MAS. The results of these studies provide a foundation for vitamin A biofortification through genomics-assisted breeding.