Abstract
CRISPR/Cas, one of the most rapidly developing technologies in the world, has been applied successfully in plant science. To test new nucleases, gRNA expression systems and other inventions in this field, several plant genes with visible phenotypic effects have been constantly used as targets. Anthocyanin pigmentation is one of the most easily identified traits, that does not require any additional treatment. It is also associated with stress resistance, therefore plants with edited anthocyanin genes might be of interest for agriculture. Phenotypic effect of CRISPR/Cas editing of PAP1 and its homologs, DFR, F3H and F3′H genes have been confirmed in several distinct plant species. DFR appears to be a key structural gene of anthocyanin biosynthesis, controlled by various transcription factors. There are still many promising potential model genes that have not been edited yet. Some of them, such as Delila, MYB60, HAT1, UGT79B2, UGT79B3 and miR156, have been shown to regulate drought tolerance in addition to anthocyanin biosynthesis. Genes, also involved in trichome development, such as TTG1, GLABRA2, MYBL2 and CPC, can provide increased visibility. In this review successful events of CRISPR/Cas editing of anthocyanin genes are summarized, and new model genes are proposed. It can be useful for molecular biologists and genetic engineers, crop scientists, plant genetics and physiologists.
Highlights
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The clustered regularly interspaced short palindromic repeats (CRISPR) system had been occasionally discovered in bacteria at the end of the XXth century, but only in the last 10 years was it applied for precise genome editing in mammalian cells and plants [1,2,3,4]
MYB1 gene cannot be used as a universal target for genome editing in many plant species. It several species, such as onion and strawberry, where MYB1 loss of function mutations have already been studied, this gene can be of some interest within the framework of CRISPR/Cas editing (Table 2)
Summary
Anthocyanins are secondary metabolites, contributing to the red, purple and blue pigmentation in all tissues of higher plants. Anthocyanin biosynthesis pathway and all structural and regulatory genes involved in it are well studied in many plant species (Figure 1). Transcription factors MYB, bHLH (MYC) and WD40 control the expression of late structural genes by binding to specific cis-acting elements in their promoter regions [41,50,51,52,53]. These three types of transcription factors form MBW complexes. Combination of MYB and bHLH transcription factors are required for anthocyanin biosynthesis regulation in Arabidopsis, but they can act alone in maize [60]. Ectopic expression of the same gene in different varieties of the same species can result in accumulation of anthocyanins in various tissues and organs [61]
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