Identification and transcript analysis of MATE genes involved in anthocyanin transport in radish ( Raphanus sativus L.)

Abstract Radish is rich in anthocyanin pigments which are beneficial both to plants and humans. Although the anthocyanin synthesis has been widely investigated, limited information is available on the mechanism underlying transport of these pigments. Recent research indicates that Multi-drug and toxic extrusion proteins (MATE) are possible anthocyanin transporters. In the present study, a total of 51 deferentially expressed transcripts (DETs) were annotated as MATEs, with 21 and 30 transcripts up-regulated at the cortex splitting and taproot thickening stages, respectively. The RsMATE proteins comprised of 490–510 residues and phylogeny analysis clustered RsMATE2, RsMATE3, RsMATE7, RsMATE8 and RsMATE9 with anthocyanin MATE transporters, implying that they might be involved in the transport of anthocyanin in radish. RT-qPCR revealed that transcript levels of RsMATE2 , RsMATE3 , RsMATE7 , RsMATE8 and RsMATE9 were significantly expressed in all colored tissues at both pre-cortex splitting and cortex splitting stages. The expression pattern indicated RsMATE5 is involved in both anthocyanin transport and other secondary metabolites due to its commensurate expression in both the colored and non-colored radish. Microscopic analysis of the spatial distribution of anthocyanin in radish was also performed, and provided evidence that anthocyanin is differentially translocated in plant tissues. Additionally, reciprocal grafting indicated that long distance transport is involved in the sequestration of anthocyanin in radish. These results show that anthocyanin type MATE transporter genes might be involved in the mutual movement of anthocyanin across cell membranes in conjunction with other mechanisms, which provided fundamental information for clarification of mechanism underlying anthocyanin accumulation and facilitated development of nutritionally enhanced taproots in radish.