Evaluation of the potential for interspecific hybridization between Camelina sativa and related wild Brassicaceae in anticipation of field trials of GM camelina

Overcoming genetic paucity of Camelina sativa: possibilities for interspecific hybridization conditioned by the genus evolution pathway

Camelina or false flax (Camelina sativa) is an emerging oilseed crop and a feedstock for biofuel production. This species is believed to originate from Western Asian and Eastern European regions, where the center of diversity of the Camelina genus is located. Cultivated Camelina species arose via a series of polyploidization events, serving as bottlenecks narrowing genetic diversity of the species. The genetic paucity of C. sativa is foreseen as the most crucial limitation for successful breeding and improvement of this crop. A potential solution to this challenge could be gene introgression from Camelina wild species or from resynthesized allohexaploid C. sativa. However, both approaches would require a complete comprehension of the evolutionary trajectories that led to the C. sativa origin. Although there are some studies discussing the origin and evolution of Camelina hexaploid species, final conclusions have not been made yet. Here, we propose the most complete integrated evolutionary model for the Camelina genus based on the most recently described findings, which enables efficient improvement of C. sativa via the interspecific hybridization with its wild relatives. We also discuss issues of interspecific and intergeneric hybridization, aimed on improving C. sativa and overcoming the genetic paucity of this crop. The proposed comprehensive evolutionary model of Camelina species indicates that a newly described species Camelina neglecta has a key role in origin of tetra- and hexaploids, all of which have two C. neglecta-based subgenomes. Understanding of species evolution within the Camelina genus provides insights into further research on C. sativa improvements via gene introgression from wild species, and a potential resynthesis of this emerging oilseed crop.

Realizing the Potential of Camelina sativa as a Bioenergy Crop for a Changing Global Climate

Camelina sativa (L.) Crantz. is an annual oilseed crop within the Brassicaceae family. C. sativa has been grown since as early as 4000 BCE. In recent years, C. sativa received increased attention as a climate-resilient oilseed, seed meal, and biofuel (biodiesel and renewable or green diesel) crop. This renewed interest is reflected in the rapid rise in the number of peer-reviewed publications (>2300) containing “camelina” from 1997 to 2021. An overview of the origins of this ancient crop and its genetic diversity and its yield potential under hot and dry growing conditions is provided. The major biotic barriers that limit C. sativa production are summarized, including weed control, insect pests, and fungal, bacterial, and viral pathogens. Ecosystem services provided by C. sativa are also discussed. The profiles of seed oil and fatty acid composition and the many uses of seed meal and oil are discussed, including food, fodder, fuel, industrial, and medical benefits. Lastly, we outline strategies for improving this important and versatile crop to enhance its production globally in the face of a rapidly changing climate using molecular breeding, rhizosphere microbiota, genetic engineering, and genome editing approaches.

Phenotypic Examination of Camelina sativa (L.) Crantz Accessions from the USDA-ARS National Genetics Resource Program

Camelina sativa (L.) Crntz. is a hardy self-pollinated oilseed plant that belongs to the Brassicaceae family; widely grown throughout the northern hemisphere until the 1940s for production of vegetable oil but was later displaced by higher-yielding rapeseed and sunflower crops. However, interest in camelina as an alternative oil source has been renewed due to its high oil content that is rich in polyunsaturated fatty acids, antioxidants as well as its ability to grow on marginal lands with minimal requirements. For this reason, our group decided to screen the existing (2011) National Genetic Resources Program (NGRP) center collection of camelina for its genetic diversity and provide a phenotypic evaluation of the cultivars available. Properties evaluated include seed and oil traits, developmental and mature morphologies, as well as chromosome content. Selectable marker genes were also evaluated for potential use in biotech manipulation. Data is provided in a raw uncompiled format to allow other researchers to analyze the unbiased information for their own studies. Our evaluation has determined that the NGRP collection has a wide range of genetic potential for both breeding and biotechnological manipulation purposes. Accessions were identified within the NGRP collection that appear to have desirable seed harvest weight (5.06 g/plant) and oil content (44.1%). Other cultivars were identified as having fatty acid characteristics that may be suitable for meal and/or food use, such as low (<2%) erucic acid content, which is often considered for healthy consumption and ranged from a high of 4.79% to a low of 1.83%. Descriptive statistics are provided for a breadth of traits from 41 accessions, as well as raw data, and key seed traits are further explored. Data presented is available for public use.

Evaluation of the progeny produced by interspecific hybridization between Camelina sativa and C. microcarpa

BACKGROUND AND AIMS

Camelina (Camelina sativa, Brassicaceae) has attracted interest in recent years as a novel oilseed crop, and an increasing number of studies have sought to enhance camelina's yield potential or to modify the composition of its oil. The ability of camelina to cross-hybridize with its wild relative, C. microcarpa, is of interest as a potential source of genetic variability for the crop.

METHODS

Manual crosses were performed between the crop C. sativa and its wild relative C. microcarpa; F1 and F2 progenies were obtained. Cytology was used to study meiosis in the parents and F1s and to evaluate pollen viability. Flow cytometry was used to estimate nuclear DNA amounts and fatty acid methyl ester analysis was used to evaluate the lipid composition of F3 seeds.

KEY RESULTS

The F1 plants obtained by interspecific crossing presented severe abnormalities at meiosis and low pollen viability, and produced very few F2 seeds. The F2s presented diverse phenotypes and in some cases severe developmental abnormalities. Many F2s were aneuploid. The F2s produced highly variable numbers of F3 seeds, and certain F3 seeds presented atypical lipid profiles.

CONCLUSIONS

Considering the meiotic abnormalities observed and the probability of aneuploidy in the F2 plants, the C. microcarpa accessions used in this study would be difficult to use as sources of genetic variability for the crop.

Intestinal Availability and Metabolic Effects of Dietary Camelina Sphingolipids during the Metabolic Syndrome Onset in Mice

Sphingolipids appear as a promising class of components susceptible to prevent the onset of the metabolic syndrome (MetS). Gut availability and effects of Camelina sativa sphingolipids were investigated in a mouse model of dietary-induced MetS. Seed meals from two Camelina sativa lines enriched, respectively, in C24- and C16-NH_2^- glycosyl-inositol-phosphoryl-ceramides (NH₂GIPC) were used in hypercaloric diets. After 5 weeks on these two hypercaloric diets, two markers of the MetS were alleviated (adiposity and insulin resistance) as well as inflammation markers and colon barrier dysfunction. A more pronounced effect was observed with the C16-NH₂GIPC-enriched HC diet, in particular for colon barrier function. Despite a lower digestibility, C16-NH₂GIPC were more prevalent in the intestine wall. Sphingolipids provided as camelina meal can therefore counteract some deleterious effects of a hypercaloric diet in mice at the intestinal and systemic levels. Interestingly, these beneficial effects seem partly dependent on sphingolipid acyl chain length.

Selective gene dosage by CRISPR-Cas9 genome editing in hexaploid Camelina sativa

In many plant species, gene dosage is an important cause of phenotype variation. Engineering gene dosage, particularly in polyploid genomes, would provide an efficient tool for plant breeding. The hexaploid oilseed crop Camelina sativa, which has three closely related expressed subgenomes, is an ideal species for investigation of the possibility of creating a large collection of combinatorial mutants. Selective, targeted mutagenesis of the three delta-12-desaturase (FAD2) genes was achieved by CRISPR-Cas9 gene editing, leading to reduced levels of polyunsaturated fatty acids and increased accumulation of oleic acid in the oil. Analysis of mutations over four generations demonstrated the presence of a large variety of heritable mutations in the three isologous CsFAD2 genes. The different combinations of single, double and triple mutants in the T3 generation were isolated, and the complete loss-of-function mutants revealed the importance of delta-12-desaturation for Camelina development. Combinatorial association of different alleles for the three FAD2 loci provided a large diversity of Camelina lines with various lipid profiles, ranging from 10% to 62% oleic acid accumulation in the oil. The different allelic combinations allowed an unbiased analysis of gene dosage and function in this hexaploid species, but also provided a unique source of genetic variability for plant breeding.

Proteome rebalancing in transgenic Camelina occurs within the enlarged proteome induced by β-carotene accumulation and storage protein suppression

Oilseed crops are global commodities for their oil and protein seed content. We have engineered the oilseed Camelina sativa to exhibit increased protein content with a slight decrease in oil content. The introduction of a phytoene synthase gene with an RNAi cassette directed to suppress the storage protein 2S albumin resulted in seeds with an 11-24 % elevation in overall protein. The phytoene synthase cassette alone produced enhanced β-carotene content of an average 275 ± 6.10 μg/g dry seed and an overall altered seed composition of 11 % less protein and comparable nontransgenic amounts of both oil and carbohydrates. Stacking an RNAi to suppress the major 2S storage protein resulted in seeds that contain elevated protein and slight decrease in oil and carbohydrate amounts showing that Camelina rebalances its proteome within an enlarged protein content genotype. In both β-carotene enhanced seeds with/without RNAi2S suppression, the seed size was noticeably enlarged compared to nontransgenic counterpart seeds. Metabolic analysis of maturing seeds indicate that the enhanced β-carotene trait had the larger effect than the RNAi2S suppression on the seed metabolome. The use of a GRAS (generally regarded as safe) β-carotene as a visual marker in a floral dip transformation system, such as Camelina, might eliminate the need for costly regulatory and controversial antibiotic resistance markers. β-carotene enhanced RNAi2S suppressed Camelina seeds could be further developed as a rapid heterologous protein production platform in a nonfood crop leveraging its enlarged protein content and visual marker.