Identification and Functional Characterization of Tomato CircRNAs Derived from Genes Involved in Fruit Pigment Accumulation

CircRNAs, a class of widespread circular RNAs produced from precursor mRNA back-splicing, have been implicated in regulation of gene expression in eukaryotes, but their biological functions in plants have not yet been elucidated. By deep sequencing of rRNA-removed and RNase R-digested RNA samples we have identified several thousands of putative back-splicing sites in tomato fruit ( Solanum lycopersicum ) and show that the abundance of some of these circRNAs derived from fruit pigment biosynthesis genes are regulated by fruit ripening. Herein, we overexpressed a circRNA derived from Phytoene Synthase 1 ( PSY1 ) in tomato ‘Ailsa Craig’ and microTom. The PSY1 mRNA abundance, the lycopene and β-carotene accumulation were decreased significantly in the transgenic tomato fruits, likely due to the continuous highly expressed circRNAs and/or the low abundant linear RNAs generated from the overexpression vector. Besides, overexpression of a circRNA derived from Phytoene Desaturase ( PDS ) showed similar results. Our results provide biological insights into plant circRNAs.