Supplemental light triggers vesicular trafficking in ripening berry accumulating anthocyanins
The transportation of anthocyanins into vacuoles is usually trafficked intra-cellularly by different classes of transporter proteins, such as MATEs, ABCs, and GSTs (Petrussa et al., 2013). The transporters involved in fruit anthocyanin transport in relation to light quality response have not been studied. However, our results demonstrated that a set of genes, including Stx , Bos1, Gos1, Ykt6, Sec20, Sec 22, andSyp7 were highly up-regulated in response to red light treatment. These genes belonged to the SNARE-domain protein family, which includes the common syntaxin-like (Stx, Syp ) genes. Interestingly, the unigenes annotated as Stx -like (1,4) type along with an ABC transporter were up-regulated in response to red light treatment and reacted in the opposite manner to that of blue light treatment. Hence, SNARE domain transporters are candidates to be involved in vesicular trafficking of anthocyanins or trans-membrane transport from endoplasmic reticulum (ER) to golgi and endosomes. It also indicates the potential role of syntaxin genes differentially responding to light-induced anthocyanin transport mechanisms. These different types of SNAREs, barring the ER localized Syp and Sec are usually localized in endosomes and in trans-golgi network (Kim et al., 2012). Our results may indicate a new route for anthocyanin sequestration and transportation in fruit tissues. The proposed vesicular trafficking model of anthocyanins in fruits might be also co-regulated by otherGST s and ABC transporters in addition to the SNARE-domain type proteins before depositing as anthocyanic vacuolar inclusions (AVI) in the vacuole (Zhao, 2015). This mechanism could also relate to the plant tissues that accumulate higher anthocyanin levels under high intensity light and needs to be investigated further.