Exploring the Potential Applications of the Noninvasive Reporter Gene IRUBY/I in Plant Genetic Transformation

Betalains can be conveniently observed and quantified and, accordingly, have the potential as naked-eye visual screening reporters during plant transformation. RUBY is a new reporter system that uses “2A” peptides to fuse three key genes, CYP76AD1, DODA, and glucosyl transferase, for betalain biosynthesis, and has been successfully used for transformation of rice, Arabidopsis, and cotton, but its potential applications in the genetic transformation of various other plant species remain to be verified. In this study, RUBY was transferred into the hairy roots of Plukenetia volubilis and Nicotiana benthamiana, and was transferred into Arabidopsis by the floral-dip method. The expression levels of CYP76AD1, DODA, and glucosyl transferase were detected by RT−PCR and RT−qPCR, the relationship between the expression level of RUBY and red coloration was analyzed, and the genetic stability of RUBY in transgenic Arabidopsis was studied. The results showed that the expression of RUBY could reconstruct the betalain biosynthesis pathway in the hairy roots of P. volubilis, N. benthamiana, and Arabidopsis plants, indicating that it has the potential for versatile use across species. As a reporter, betalain did not affect callus induction, plant regeneration, development, or fertility. However, when used in plant transformation for observation and visual screening, it needed to accumulate to a certain extent to show red coloration, and it was positively correlated with gene expression. In general, RUBY is a convenient reporter for plant transformation, and has no obvious side effects during plant growth and development. However, the potential application of RUBY for visual screening is highly determined by the expression level, and further improvement is needed.