Genetic dissection of natural variation in oilseed traits of camelina by whole-genome resequencing and QTL mapping

Genetic study of Camelina sativa oilseed crop and selection of a new variety by the bulk method

Camelina sativa, commonly referred to as camelina or false flax, has emerged as a promising cover crop with the potential to mitigate climate change-a pressing global challenge that demands urgent and sustainable solutions. Belonging to the Brassicaceae family and native to Europe and Central Asia, camelina is an oilseed crop known for its resilience in diverse climates, including arid and semi-arid regions, making it adaptable to various environments. A breeding program started from a study of six winter varieties and five spring varieties of camelina is described: these genetic materials were characterized by SSRs molecular markers and by GBS technique. Molecular data clearly showed all spring varieties were genetically similar and distinguishable from the winter varieties, which, in turn, clustered together. Using molecular data, parental varieties belonging to the two different clusters were selected to generate new genetic variability. The new variety obtained, selected through the bulk method based on three parameters: yield, earliness, and weight of 1000 seeds, has allowed the generation of the new genetic material provisionally named C1244. Chemical characterization was performed (bromatological and glucosinolates analysis) to better describe C1244 in comparison with benchmark varieties. The new variety exhibited early maturity, similar to spring varieties, making this genetic material promising for use in intercropping systems, a high weight of 1000 seeds (1.46 g) which improves and facilitates seeding/harvesting operations and a high oil content (33.62%) akin to winter varieties making it valuable for human and animal food purposes.

Heat stress during reproductive stages reduces camelina seed productivity and changes seed composition

Camelina (Camelina sativa L. Crantz) is a low-input oilseed crop with great potential in bioenergy and industrial oils. Improving tolerance to high temperatures is essential for camelina agronomic sustainability. Two genotypes, Suneson and Pryzeth, were exposed to a transient 14-day heat stress at 37 °C during the reproductive stages. Four cohorts of pods along the main stem, which were at different stages from fully developed pods (C1), young pods (C2), open flowers (C3) and flowering buds (C4) at the time of heat treatment, were examined for morphological and seed quality traits at maturity. The main stem length was shortened in both genotypes. Pods and seeds in all cohorts were negatively affected by heat, resulting in lower seed yield and reduced oil content. Seed size and seed weight had the greatest reduction in C1, pod size reduction was found the most in C3, and the number of fertile pods that contain at least one seed was reduced in C3 and C4. These results suggest that heat stress effects are developmental stage specific. Heat stress significantly reduced fertility during flowering and inhibited storage product biosynthesis and accumulation during seed filling which resulted in smaller and lighter seeds. Analyzing seed composition indicated that oil content decreased while protein content increased in seeds from heat treated plants. In addition, fatty acid composition was altered with the reduction of omega-3 α-linolenic acid and concomitantly increased omega-6 linoleic acid being the most significantly affected. Our results also revealed the different responses in the two genotypes examined, suggesting genetic variation in camelina germplasm which can be explored to improve heat tolerance. This study provides resources and guidance for future studies to understand genetic and physiological mechanisms of heat stress and to assist in improving the sustainability of camelina production facing climate change.

Mapping QTL for vernalization requirement identified adaptive divergence of the candidate gene Flowering Locus C in polyploid Camelina sativa

Vernalization requirement is an integral component of flowering in winter-type plants. The availability of winter ecotypes among Camelina species facilitated the mapping of quantitative trait loci (QTL) for vernalization requirement in Camelina sativa. An inter and intraspecific crossing scheme between related Camelina species, where one spring and two different sources of winter-type habit were used, resulted in the development of two segregating populations. Linkage maps generated with sequence-based markers identified three QTLs associated with vernalization requirement in C. sativa; two from the interspecific (chromosomes 13 and 20) and one from the intraspecific cross (chromosome 8). Notably, the three loci were mapped to different homologous regions of the hexaploid C. sativa genome. All three QTLs were found in proximity to Flowering Locus C (FLC), variants of which have been reported to affect the vernalization requirement in plants. Temporal transcriptome analysis for winter-type Camelina alyssum demonstrated reduction in expression of FLC on chromosomes 13 and 20 during cold treatment, which would trigger flowering, since FLC would be expected to suppress floral initiation. FLC on chromosome 8 also showed reduced expression in the C. sativa ssp. pilosa winter parent upon cold treatment, but was expressed at very high levels across all time points in the spring-type C. sativa. The chromosome 8 copy carried a deletion in the spring-type line, which could impact its functionality. Contrary to previous reports, all three FLC loci can contribute to controlling the vernalization response in C. sativa and provide opportunities for manipulating this requirement in the crop.

Cold stress induces differential gene expression of retained homeologs in Camelina sativa cv Suneson

Camelina sativa (L.) Crantz, a member of the Brassicaceae, has potential as a biofuel feedstock which is attributable to the production of fatty acids in its seeds, its fast growth cycle, and low input requirements. While a genome assembly is available for camelina, it was generated from short sequence reads and is thus highly fragmented in nature. Using long read sequences, we generated a chromosome-scale, highly contiguous genome assembly (644,491,969 bp) for the spring biotype cultivar 'Suneson' with an N50 contig length of 12,031,512 bp and a scaffold N50 length of 32,184,682 bp. Annotation of protein-coding genes revealed 91,877 genes that encode 133,355 gene models. We identified a total of 4,467 genes that were significantly up-regulated under cold stress which were enriched in gene ontology terms associated with "response to cold" and "response to abiotic stress". Coexpression analyses revealed multiple coexpression modules that were enriched in genes differentially expressed following cold stress that had putative functions involved in stress adaptation, specifically within the plastid. With access to a highly contiguous genome assembly, comparative analyses with Arabidopsis thaliana revealed 23,625 A. thaliana genes syntenic with 45,453 Suneson genes. Of these, 24,960 Suneson genes were syntenic to 8,320 A. thaliana genes reflecting a 3 camelina homeolog to 1 Arabidopsis gene relationship and retention of all three homeologs. Some of the retained triplicated homeologs showed conserved gene expression patterns under control and cold-stressed conditions whereas other triplicated homeologs displayed diverged expression patterns revealing sub- and neo-functionalization of the homeologs at the transcription level. Access to the chromosome-scale assembly of Suneson will enable both basic and applied research efforts in the improvement of camelina as a sustainable biofuel feedstock.

Oilomics: An important branch of foodomics dealing with oil science and technology

Oil is one of three nutritious elements. The application of omics techniques in the field of oil science and technology is attracted increasing attention. Oilomics, which emerged as an important branch of foodomics, has been widely used in various aspects of oil science and technology. However, there are currently no articles systematically reviewing the application of oilomics. This paper aims to provide a critical overview of the advantages and value of oilomics technology compared to traditional techniques in various aspects of oil science and technology, including oil nutrition, oil processing, oil quality, safety, and traceability. Moreover, this article intends to review major issues in oilomics and give a comprehensive, critical overview of the current state of the art, future challenges and trends in oilomics, with a view to promoting the optimal application and development of oilomics technology in oil science and technology.

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.

Homozygosity mapping identified loci and candidate genes responsible for freezing tolerance in Camelina sativa

Homozygosity mapping is an effective tool for detecting genomic regions responsible for a given trait when the phenotype is controlled by a limited number of dominant or co-dominant loci. Freezing tolerance is a major attribute in agricultural crops such as camelina. Previous studies indicated that freezing tolerance differences between a tolerant (Joelle) and susceptible (CO46) variety of camelina were controlled by a small number of dominant or co-dominant genes. We performed whole genome homozygosity mapping to identify markers and candidate genes responsible for freezing tolerance difference between these two genotypes. A total of 28 F3 RILs were sequenced to ∼30× coverage, and parental lines were sequenced to >30-40× coverage with Pacific Biosciences high fidelity technology and 60× coverage using Illumina whole genome sequencing. Overall, about 126k homozygous single nucleotide polymorphism markers were identified that differentiate both parents. Moreover, 617 markers were also homozygous in F3 families fixed for freezing tolerance/susceptibility. All these markers mapped to two contigs forming a contiguous stretch of chromosome 11. The homozygosity mapping detected 9 homozygous blocks among the selected markers and 22 candidate genes with strong similarity to regions in or near the homozygous blocks. Two such genes were differentially expressed during cold acclimation in camelina. The largest block contained a cold-regulated plant thionin and a putative rotamase cyclophilin 2 gene previously associated with freezing resistance in arabidopsis (Arabidopsis thaliana). The second largest block contains several cysteine-rich RLK genes and a cold-regulated receptor serine/threonine kinase gene. We hypothesize that one or more of these genes may be primarily responsible for freezing tolerance differences in camelina varieties.

Genetic Improvement of Camelina sativa (L.) Crantz: Opportunities and Challenges

In recent years, a renewed interest in novel crops has been developing due to the environmental issues associated with the sustainability of agricultural practices. In particular, a cover crop, Camelina sativa (L.) Crantz, belonging to the Brassicaceae family, is attracting the scientific community's interest for several desirable features. It is related to the model species Arabidopsis thaliana, and its oil extracted from the seeds can be used either for food and feed, or for industrial uses such as biofuel production. From an agronomic point of view, it can grow in marginal lands with little or no inputs, and is practically resistant to the most important pathogens of Brassicaceae. Although cultivated in the past, particularly in northern Europe and Italy, in the last century, it was abandoned. For this reason, little breeding work has been conducted to improve this plant, also because of the low genetic variability present in this hexaploid species. In this review, we summarize the main works on this crop, focused on genetic improvement with three main objectives: yield, seed oil content and quality, and reduction in glucosinolates content in the seed, which are the main anti-nutritional substances present in camelina. We also report the latest advances in utilising classical plant breeding, transgenic approaches, and CRISPR-Cas9 genome-editing.

Genome-Wide Identification and Expression Analysis of Fatty Acid Desaturase (FAD) Genes in Camelina sativa (L.) Crantz

Camelina sativa (L.) Crantz is an indispensable oilseed crop, and its seeds contain many unsaturated fatty acids. FAD (fatty acid desaturase) regulates the synthesis of unsaturated fatty acids. In this research, we performed CsFAD gene family analysis and identified 24 CsFAD genes in Camelina, which were unevenly distributed on 14 of the 19 total chromosomes. Phylogenetic analysis showed that CsFAD includes four subfamilies, supported by the conserved structures and motifs of CsFAD genes. In addition, we investigated the expression patterns of the FAD family in the different tissues of Camelina. We found that CsFAD family genes were all expressed in the stem, and CsFAD2-2 was highly expressed in the early stage of seed development. Moreover, during low temperature (4 °C) stress, we identified that the expression level of CsFAD2-2 significantly changed. By observing the transient expression of CsFAD2-2 in Arabidopsis protoplasts, we found that CsFAD2-2 was located on the nucleus. Through the detection and analysis of fatty acids, we prove that CsFAD2-2 is involved in the synthesis of linolenic acid (C18:3). In conclusion, we identified CsFAD2-2 through the phylogenetic analysis of the CsFAD gene family and further determined the fatty acid content to find that CsFAD2-2 is involved in fatty acid synthesis in Camelina.

The identification of the missing maternal genome of the allohexaploid camelina (Camelina sativa)

Hexaploid camelina (Camelina sativa; 2n = 6x = 40) is an important oilseed crop closely related to Arabidopsis. Compared to other polyploid crops, the origin of the three camelina subgenomes has begun to be unveiled only recently. While phylogenomic studies identified the diploid C. hispida (2n = 2x = 14) as the paternal genome of C. sativa, the maternal donor genome remained unknown. Because the chromosomes assigned to a putative maternal genome resembled those of diploid C. neglecta (2n = 12), a tetraploid C. neglecta-like genome (2n = 4x = 26) was hypothesized to be the likely maternal ancestor of the hexaploid crop. Here we report the chromosome-level structure of the predicted tetraploid Camelina genome identified among genotypes previously classified together as C. microcarpa and referred to here as C. intermedia. Detailed cytogenomic analysis of the tetraploid genome revealed high collinearity with two maternally inherited subgenomes of the hexaploid C. sativa. The identification of the missing donor tetraploid genome provides new insights into the reticulate evolutionary history of the Camelina polyploid complex and allows us to postulate a comprehensive evolutionary model for the genus. The herein elucidated origin of the C. sativa genome opens the door for subsequent genome modifications and resynthesis of the allohexaploid camelina genome.

Molecular and archaeological evidence on the geographical origin of domestication for Camelina sativa

PREMISE

Camelina (gold-of-pleasure or false flax) is an ancient oilseed crop with emerging applications in the production of sustainable, low-input biofuels. Previous domestication hypotheses suggested a European or western Asian origin, yet little genetic evidence has existed to assess the geographical origin for this crop, and archaeological data have not been systematically surveyed.

METHODS

We utilized genotyping-by-sequencing of 185 accessions of C. sativa and its wild relatives to examine population structure within the crop species and its relationship to populations of its wild progenitor, C. microcarpa; cytotype variation was also assessed in both species. In a complementary analysis, we surveyed the archaeological literature to identify sites with archaeobotanical camelina remains and assess the timing and prevalence of usage across Europe and western Asia.

RESULTS

The majority of C. microcarpa sampled in Europe and the United States belongs to a variant cytotype (2n = 38) with a distinct evolutionary origin from that of the crop lineage (2n = 40). Populations of C. microcarpa from Transcaucasia (South Caucasus) are most closely related to C. sativa based on cytotype and population structure; in combination with archaeological insights, these data refute prior hypotheses of a European domestication origin.

CONCLUSIONS

Our findings support a Caucasus, potentially Armenian, origin of C. sativa domestication. We cannot definitively determine whether C. sativa was intentionally targeted for domestication in its own right or instead arose secondarily through selection for agricultural traits in weedy C. sativa, as originally proposed by Vavilov for this species.