Laser capture microdissection transcriptome (LCM RNA-seq) reveals BcDFR is a key gene in anthocyanin synthesis of Non-heading Chinese cabbage

Abstract Background: Non-heading Chinese cabbage [Brassica campestris (syn. Brassica rapa) ssp. chinensis]is an important leafy vegetable that is mainly grown in Asian. Purple non-heading Chinese cabbage has become popular because of it rich in anthocyanin. However, since anthocyanins only accumulate in the upper epidermis of leaves, further studies are needed to investigate the molecular mechanisms underlying the specific accumulation of anthocyanins in the upper epidermis of leaves. Results: In this study, we used laser capture frozen section method (LCM) to divide purple (ZBC) and green (LBC) non-heading Chinese cabbage leaves into upper and lower epidermis parts (ZS represents the purple upper epidermis, ZX represents the purple lower epidermis, LS represents the green upper epidermis, LX represents the green lower epidermis). Through transcriptome sequencing, we found that the DIHYDROFLAVONOL 4-REDUCTASE-encoding gene BcDFR, shows highly expressed in ZS but hardly in others (ZX, LS, LX). Further, a deletion and insertion in the promoter of BcDFR in LBC was found, which may interfere BcDFRexpression. Subsequent analysis of gene structure and conserved structural domains showed that BcDFR is highly conserved in Brassica species. Predicted protein-protein interaction network of BcDFR suggests that it interacts with almost all functional proteins in the anthocyanin biosynthesis pathway. Finally, the results of the tobacco transient expression also demonstrated that BcDFR promotes the synthesis and accumulation of anthocyanin. Conclusions: BcDFRis specifical highly expressed on the upper epidermis of purple non-heading Chinese cabbage leaves and regulates anthocyanin biosynthesis and accumulation. Our study provides new insights into the functional analysis and transcriptional regulatory network of anthocyanin-related genes in purple non-heading Chinese cabbage.