Genome-Scale Analysis of the WRI-Like Family in Gossypium and Functional Characterization of GhWRI1a Controlling Triacylglycerol Content

Multi-omics-driven advances in the understanding of triacylglycerol biosynthesis in oil seeds

Vegetable oils are rich sources of polyunsaturated fatty acids and energy as well as valuable sources of human food, animal feed, and bioenergy. Triacylglycerols, which are comprised of three fatty acids attached to a glycerol backbone, are the main component of vegetable oils. Here, we review the development and application of multiple-level omics in major oilseeds and emphasize the progress in the analysis of the biological roles of key genes underlying seed oil content and quality in major oilseeds. Finally, we discuss future research directions in functional genomics research based on current omics and oil metabolic engineering strategies that aim to enhance seed oil content and quality, and specific fatty acids components according to either human health needs or industrial requirements.

Genomic and co-expression network analyses reveal candidate genes for oil accumulation based on an introgression population in Upland cotton (Gossypium hirsutum)

KEY MESSAGE

Integrated QTL mapping and WGCNA condense the potential gene regulatory network involved in oil accumulation. A glycosyl hydrolases gene (GhHSD1) for oil biosynthesis was confirmed in Arabidopsis, which will provide useful knowledge to understand the functional mechanism of oil biosynthesis in cotton. Cotton is an economical source of edible oil for the food industry. The genetic mechanism that regulates oil biosynthesis in cottonseeds is essential for the genetic enhancement of oil content (OC). To explore the functional genomics of OC, this study utilized an interspecific backcross inbred line population to dissect the quantitative trait locus (QTL) interlinked with OC. In total, nine OC QTLs were identified, four of which were novel, and each QTL explained 3.62-34.73% of the phenotypic variation of OC. The comprehensive transcript profiling of developing cottonseeds revealed 3,646 core genes differentially expressed in both inbred parents. Functional enrichment analysis determined 43 genes were annotated with oil biosynthesis processes. Implementation of weighted gene co-expression network analysis showed that 803 differential genes had a significant correlation with the OC phenotype. Further integrated analysis identified seven important genes located in OC QTLs. Of which, the GhHSD1 gene located in stable QTL qOC-Dt3-1 exhibited the highest functional linkages with the other network genes. Phylogenetic analysis showed significant evolutionary differences in the HSD1 sequences between oilseed- and starch- crops. Furthermore, the overexpression of GhHSD1 in Arabidopsis yielded almost 6.78% higher seed oil. This study not only uncovers important genetic loci for oil accumulation in cottonseed, but also provides a set of new candidate genes that potentially influence the oil biosynthesis pathway in cottonseed.

Oil candidate genes in seeds of cotton (Gossypium hirsutum L.) and functional validation of GhPXN1

BACKGROUND

Cottonseed oil is a promising edible plant oil with abundant unsaturated fatty acids. However, few studies have been conducted to explore the characteristics of cottonseed oil. The molecular mechanism of cottonseed oil accumulation remains unclear.

RESULTS

In the present study, we conducted comparative transcriptome and weighted gene co-expression network (WGCNA) analysis for two G. hirsutum materials with significant difference in cottonseed oil content. Results showed that, between the high oil genotype 6053 (H6053) and the low oil genotype 2052 (L2052), a total of 412, 507, 1,121, 1,953, and 2,019 differentially expressed genes (DEGs) were detected at 10, 15, 20, 25, and 30 DPA, respectively. Remarkably, a large number of the down-regulated DEGs were enriched in the phenylalanine metabolic processes. Investigation into the dynamic changes of expression profiling of genes associated with both phenylalanine metabolism and oil biosynthesis has shed light on a significant competitive relationship in substrate allocation during cottonseed development. Additionally, the WGCNA analysis of all DEGs identified eight distinct modules, one of which includes GhPXN1, a gene closely associated with oil accumulation. Through phylogenetic analysis, we hypothesized that GhPXN1 in G. hirsutum might have been introgressed from G. arboreum. Overexpression of the GhPXN1 gene in tobacco leaf suggested a significant reduction in oil content compared to the empty-vector transformants. Furthermore, ten other crucial oil candidate genes identified in this study were also validated using quantitative real-time PCR (qRT-PCR).

CONCLUSIONS

Overall, this study enhances our comprehension of the molecular mechanisms underlying cottonseed oil accumulation.

Selection pressure on the rhizosphere microbiome can alter nitrogen use efficiency and seed yield in Brassica rapa

Microbial experimental systems provide a platform to observe how networks of groups emerge to impact plant development. We applied selection pressure for microbiome enhancement of Brassica rapa biomass to examine adaptive bacterial group dynamics under soil nitrogen limitation. In the 9th and final generation of the experiment, selection pressure enhanced B. rapa seed yield and nitrogen use efficiency compared to our control treatment, with no effect between the random selection and control treatments. Aboveground biomass increased for both the high biomass selection and random selection plants. Soil bacterial diversity declined under high B. rapa biomass selection, suggesting a possible ecological filtering mechanism to remove bacterial taxa. Distinct sub-groups of interactions emerged among bacterial phyla such as Proteobacteria and Bacteroidetes in response to selection. Extended Local Similarity Analysis and NetShift indicated greater connectivity of the bacterial community, with more edges, shorter path lengths, and altered modularity through the course of selection for enhanced plant biomass. In contrast, bacterial communities under random selection and no selection showed less complex interaction profiles of bacterial taxa. These results suggest that group-level bacterial interactions could be modified to collectively shift microbiome functions impacting the growth of the host plant under soil nitrogen limitation.

Genetics, Breeding and Genetic Engineering to Improve Cottonseed Oil and Protein: A Review

Upland cotton (Gossypium hirsutum) is the world's leading fiber crop and one of the most important oilseed crops. Genetic improvement of cotton has primarily focused on fiber yield and quality. However, there is an increased interest and demand for enhanced cottonseed traits, including protein, oil, fatty acids, and amino acids for broad food, feed and biofuel applications. As a byproduct of cotton production, cottonseed is an important source of edible oil in many countries and could also be a vital source of protein for human consumption. The focus of cotton breeding on high yield and better fiber quality has substantially reduced the natural genetic variation available for effective cottonseed quality improvement within Upland cotton. However, genetic variation in cottonseed oil and protein content exists within the genus of Gossypium and cultivated cotton. A plethora of genes and quantitative trait loci (QTLs) (associated with cottonseed oil, fatty acids, protein and amino acids) have been identified, providing important information for genetic improvement of cottonseed quality. Genetic engineering in cotton through RNA interference and insertions of additional genes of other genetic sources, in addition to the more recent development of genome editing technology has achieved considerable progress in altering the relative levels of protein, oil, fatty acid profile, and amino acids composition in cottonseed for enhanced nutritional value and expanded industrial applications. The objective of this review is to summarize and discuss the cottonseed oil biosynthetic pathway and major genes involved, genetic basis of cottonseed oil and protein content, genetic engineering, genome editing through CRISPR/Cas9, and QTLs associated with quantity and quality enhancement of cottonseed oil and protein.

Identification and analysis of oil candidate genes reveals the molecular basis of cottonseed oil accumulation in Gossypium hirsutum L

Based on the integration of QTL-mapping and regulatory network analyses, five high-confidence stable QTL regions, six candidate genes and two microRNAs that potentially affect the cottonseed oil content were discovered. Cottonseed oil is increasingly becoming a promising target for edible oil with its high content of unsaturated fatty acids. In this study, a recombinant inbred line (RIL) cotton population was constructed to detect quantitative trait loci (QTLs) for the cottonseed oil content. A total of 39 QTLs were detected across eight different environments, of which five QTLs were stable. Forty-three candidate genes potentially involved in carbon metabolism, fatty acid synthesis and triacylglycerol biosynthesis processes were further obtained in the stable QTL regions. Transcriptome analysis showed that nineteen of these candidate genes expressed during  the developing cottonseed ovules and may affect the cottonseed oil content. Besides, transcription factor (TF) and microRNA (miRNA) co-regulatory network analyses based on the nineteen candidate genes suggested that six genes, two core miRNAs (ghr-miR2949b and ghr-miR2949c), and one TF GhHSL1 were considered to be closely associated with the cottonseed oil content. Moreover, four vital genes were validated by quantitative real-time PCR (qRT-PCR). These results provide insights into the oil accumulation mechanism in developing cottonseed ovules through the construction of a detailed oil accumulation model.

Genome-wide association study of the oil content in upland cotton (Gossypium hirsutum L.) and identification of GhPRXR1, a candidate gene for a stable QTLqOC-Dt5-1

Cottonseed oil is one of the most important renewable resources for edible oil and biodiesel. To detect QTLs associated with cottonseed oil content (OC) and identify candidate genes that regulate oil biosynthesis, a panel of upland cotton germplasm lines was selected among those previously used to perform GWASs in China. In the present study, 13 QTLs associated with 53 common SNPs on 13 chromosomes were identified in multiple environments based on 15,369 polymorphic SNPs using the Cotton63 KSNP array. Of these, the OC QTL qOC-Dt5-1 delineated by nine SNPs occurred in a confidence interval of 4 SSRs with previously reported OC QTLs. A combined transcriptome and qRT-PCR analysis revealed that a peroxidase gene (GhPRXR1) was predominantly expressed during the middle-late stage (20-35 days post anthesis) of ovule development. The overexpression of GhPRXR1 in yeast significantly increased the OC by 20.01-37.25 %. Suppression of GhPRXR1 gene expression in the virus-induced gene-silenced cotton reduced the OC by 18.11%. Our results contribute to identifying more OC QTLs and verifying a candidate gene that influences cottonseed oil biosynthesis.

A genome-wide analysis of the phospholipid: diacylglycerol acyltransferase gene family in Gossypium

Background

Cotton (Gossypium spp.) is the most important natural fiber crop worldwide, and cottonseed oil is its most important byproduct. Phospholipid: diacylglycerol acyltransferase (PDAT) is important in TAG biosynthesis, as it catalyzes the transfer of a fatty acyl moiety from the sn-2 position of a phospholipid to the sn-3 position of sn-1, 2-diacylglyerol to form triacylglycerol (TAG) and a lysophospholipid. However, little is known about the genes encoding PDATs involved in cottonseed oil biosynthesis.

Results

A comprehensive genome-wide analysis of G. hirsutum, G. barbadense, G. arboreum, and G. raimondii herein identified 12, 11, 6 and 6 PDATs, respectively. These genes were divided into 3 subfamilies, and a PDAT-like subfamily was identified in comparison with dicotyledonous Arabidopsis. All GhPDATs contained one or two LCAT domains at the C-terminus, while most GhPDATs contained a preserved single transmembrane region at the N-terminus. A chromosomal distribution analysis showed that the 12 GhPDAT genes in G. hirsutum were distributed in 10 chromosomes. However, none of the GhPDATs was co-localized with quantitative trait loci (QTL) for cottonseed oil content, suggesting that their sequence variations are not genetically associated with the natural variation in cottonseed oil content. Most GhPDATs were expressed during the cottonseed oil accumulation stage. Ectopic expression of GhPDAT1d increased Arabidopsis seed oil content.

Conclusions

Our comprehensive genome-wide analysis of the cotton PDAT gene family provides a foundation for further studies into the use of PDAT genes to increase cottonseed oil content through biotechnology.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5728-8) contains supplementary material, which is available to authorized users.

A genome-wide analysis of the phospholipid: diacylglycerol acyltransferase gene family in Gossypium

BACKGROUND

Cotton (Gossypium spp.) is the most important natural fiber crop worldwide, and cottonseed oil is its most important byproduct. Phospholipid: diacylglycerol acyltransferase (PDAT) is important in TAG biosynthesis, as it catalyzes the transfer of a fatty acyl moiety from the sn-2 position of a phospholipid to the sn-3 position of sn-1, 2-diacylglyerol to form triacylglycerol (TAG) and a lysophospholipid. However, little is known about the genes encoding PDATs involved in cottonseed oil biosynthesis.

RESULTS

A comprehensive genome-wide analysis of G. hirsutum, G. barbadense, G. arboreum, and G. raimondii herein identified 12, 11, 6 and 6 PDATs, respectively. These genes were divided into 3 subfamilies, and a PDAT-like subfamily was identified in comparison with dicotyledonous Arabidopsis. All GhPDATs contained one or two LCAT domains at the C-terminus, while most GhPDATs contained a preserved single transmembrane region at the N-terminus. A chromosomal distribution analysis showed that the 12 GhPDAT genes in G. hirsutum were distributed in 10 chromosomes. However, none of the GhPDATs was co-localized with quantitative trait loci (QTL) for cottonseed oil content, suggesting that their sequence variations are not genetically associated with the natural variation in cottonseed oil content. Most GhPDATs were expressed during the cottonseed oil accumulation stage. Ectopic expression of GhPDAT1d increased Arabidopsis seed oil content.

CONCLUSIONS

Our comprehensive genome-wide analysis of the cotton PDAT gene family provides a foundation for further studies into the use of PDAT genes to increase cottonseed oil content through biotechnology.