Visual Assay for Gene Editing Using a CRISPR/Cas9 System in Carrot Cells

OsGSTU34, a Bz2-like anthocyanin-related glutathione transferase transporter, is essential for rice (Oryza sativa L.) organs coloration

Anthocyanins are a flavonoid compound known as one of the most important chromogenic substances. They play several functions, including health promotion and sustaining plants during adverse conditions. They are synthesized at the endoplasmic reticulum and sequestered in the vacuole. In this work, we generated knock-out lines of OsGSTU34, a glutathione transporter's tau gene family, with no transgene line and off-target through CRISPR/Cas9 mutagenesis and highlighted the loss of pigmentation in rice flowers, leaves, stems, shoots, and caryopsis. The anthocyanin quantification in the wild-type BLWT and mutant line BLG34-8 caryopsis showed that cyanidin-3-O-glucoside (C3G) and peonidin-3-O-glucoside (P3G) were almost undetectable in the mutant line. A tandem mass tag (TMT) labeling proteomic analysis was conducted to elucidate the proteomic changes in the BLWT and BLG34-8. The result revealed that 1175 proteins were altered, including 408 that were down-regulated and 767 that were upregulated. The accumulation of the OsGSTU34-related protein (Q8L576), along with several anthocyanin-related proteins, was down-regulated. The enrichment analysis showed that the down-regulated proteins were enriched in different pathways, among which the phenylpropanoid biosynthesis pathway, flavonoid biosynthesis metabolites, and anthocyanin biosynthesis pathway. Protein interaction network prediction revealed that glutathione-S-transferase (Q8L576) was connected to the proteins involved in the flavonoid and anthocyanin biosynthesis pathways, such as flavanone 3-dioxygenase 1 (Q7XM21), leucoanthocyanidin dioxygenase 1 (Q93VC3), 4-coumarate-CoA ligase 2 (Q42982), phenylalanine ammonia-lyase (P14717), chalcone synthase 1 (Q2R3A1), and 4-coumarate-CoA ligase 5 (Q6ZAC1). However, the expression of the most important anthocyanin biosynthesis gene was not altered, suggesting that only the transport mechanism was affected. Our findings highlight new insight into the anthocyanin pigmentation in black rice and provide new perspectives for future research.

Development and Application of CRISPR/Cas9 to Improve Anthocyanin Pigmentation in Plants: Opportunities and Perspectives

Since its discovery in 2012, the novel technology of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) has greatly contributed to revolutionizing molecular biology. It has been demonstrated to be an effective approach for identifying gene function and improving some important traits. Anthocyanins are secondary metabolites responsible for a wide spectrum of aesthetic coloration in various plant organs and are beneficial for health. As such, increasing anthocyanin content in plants, especially the edible tissue and organs, is always a main goal for plant breeding. Recently, CRISPR/Cas9 technology has been highly desired to enhance the amount of anthocyanin in vegetables, fruits, cereals, and other attractive plants with more precision. Here we reviewed the recent knowledge concerning CRISPR/Cas9-mediated anthocyanin enhancement in plants. In addition, we addressed the future avenues of promising potential target genes that could be helpful for achieving the same goal using CRISPR/Cas9 in several plants. Thus, molecular biologists, genetic engineers, agricultural scientists, plant geneticists, and physiologists may benefit from CRISPR technology to boost the biosynthesis and accumulation of anthocyanins in fresh fruits, vegetables, grains, roots, and ornamental plants.

Anthocyanin metabolic engineering of Euphorbia pulcherrima: advances and perspectives

The range of floral colors is determined by the type of plant pigment accumulated by the plant. Anthocyanins are the most common flavonoid pigments in angiosperms; they provide a wide range of visible colors from red-magenta to blue-purple, products of cyanidin and delphinidin biosynthesis, respectively. For the floriculture industry, floral color is one of the most important ornamental characteristics for the development of new commercial varieties; however, most plant species are restricted to a certain color spectrum, limited by their own genetics. In fact, many ornamental crops lack bluish varieties due to the lack of activity of essential biosynthetic enzymes for the accumulation of delphinidin. An example is the poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch), the ornamental plant symbol of Christmas and native to Mexico. Its popularity is the result of the variety of colors displayed by its bracts, a kind of modified leaves that accumulate reddish pigments based mainly on cyanidin and, to a lesser extent, on pelargonidin. The commercial success of this plant lies in the development of new varieties and, although consumers like the typical red color, they are also looking for poinsettias with new and innovative colors. Previous research has demonstrated the possibility of manipulating flower color through metabolic engineering of the anthocyanin biosynthesis pathway and plant tissue culture in different ornamental plant species. For example, transgenic cultivars of flowers such as roses, carnations or chrysanthemums owe their attractive bluish colors to a high and exclusive accumulation of delphinidin. Here, we discuss the possibilities of genetic engineering of the anthocyanin biosynthetic pathway in E. pulcherrima through the introduction of one or more foreign delphinidin biosynthetic genes under the transcriptional control of a pathway-specific promoter, and the genome editing possibilities as an alternative tool to modify the color of the bracts. In addition, some other approaches such as the appropriate selection of the cultivars that presented the most suitable intracellular conditions to accumulate delphinidin, as well as the incorporation of genes encoding anthocyanin-modifying enzymes or transcription factors to favor the bluish pigmentation of the flowers are also revised.

Discovery of genes involved in anthocyanin biosynthesis from the rind and pith of three sugarcane varieties using integrated metabolic profiling and RNA-seq analysis

BACKGROUND

Sugarcane (Saccharum officinarum) is one of the most valuable feedstocks for sugar production. In addition to the production of industrial raw materials such as alcohol, papermaking, the fiber of livestock feed, respectively, sugarcane can produce bioactive compounds such as anthocyanins. Elucidation of the anthocyanin biosynthesis pathway is critical for the molecular breeding of sugarcane varieties with favorable traits. We aimed to identify candidate genes involved in anthocyanin biosynthesis by transcriptomic and metabolomic analyses.

RESULTS

Three varieties of sugarcane displaying different colors were used in this study: FN15 (greed rind), ROC22 (red rind), and Badila (purple rind). Sample materials were subjected to metabolomic analysis using UPLC-Q-TOF/MS and RNA-seq analysis. The metabolomic profiling results showed Cyanidin, Cyanidin (6'-malonylglucoside), Cyanidin O-glucoside, and Peonidin O-glucoside were the main components responsible for the rind color. Then, through RNA-seq analysis, we identified a total of 3137, 3302, 3014 differentially expressed genes (DEGs) between the rind and pith tissues for the corresponding varieties Badila rind, ROC22, and FN15. We then compared the expression levels of genes among the rind tissues from the three varieties. We identified 2901, 2821, and 3071 DEGs between Badila rind vs. ROC22 rind, Badila rind vs. FN15 rind, ROC22 rind vs. FN15 rind, respectively. We identified two enriched pathways, including phenylpropanoid biosynthesis and flavonoid biosynthesis. Sequencing similarity search identified a total of 50 unigenes belonging to 15 enzyme families as putative genes involved in anthocyanin biosynthesis in sugarcane rind. Seven of them were identified as candidate genes related to anthocyanin biosynthesis in the rind of sugarcane through co-localization analysis with the anthocyanin content in sugarcane. In total, 25 unigenes were selected and subjected to RT-qPCR analysis, and qRT-PCR results were consistent with those obtained with the RNA-Seq experiments.

CONCLUSIONS

We proposed a pathway for anthocyanin biosynthesis in sugarcane rind. This is the first report on the biosynthesis of anthocyanin in sugarcane using the combined transcriptomic and metabolomic methods. The results obtained from this study will lay the foundation for breeding purple pith sugarcane varieties with high anthocyanin contents.