Transcriptomic profiling of purple broccoli reveals light-induced anthocyanin biosynthetic signaling and structural genes

Chunqing Liu; Xueqin Yao; Guangqing Li; Lei Huang; Zhujie Xie

doi:10.7717/peerj.8870

Transcriptomic profiling of purple broccoli reveals light-induced anthocyanin biosynthetic signaling and structural genes

PeerJ. 2020 May 5:8:e8870. doi: 10.7717/peerj.8870. eCollection 2020.

Authors

Chunqing Liu^#¹, Xueqin Yao^#¹, Guangqing Li¹, Lei Huang², Zhujie Xie¹

Affiliations

¹ Shanghai Academy of Agricultural Sciences, Institute of Horticulture, Shanghai, China.
² School of Ecological Technology and Engineering, Shanghai Institute of Technology, Shanghai, China.

^# Contributed equally.

Abstract

Purple Broccoli (Brassica oleracea L. var italica) attracts growing attention as a functional food. Its purple coloration is due to high anthocyanin amounts. Light represents a critical parameter affecting anthocyanins biosynthesis. In this study, 'Purple Broccoli', a light-responding pigmentation cultivar, was assessed for exploring the mechanism underlying light-induced anthocyanin biosynthesis by RNA-Seq. Cyanidin, delphinidin and malvidin derivatives were detected in broccoli head samples. Shading assays and RNA-seq analysis identified the flower head as more critical organ compared with leaves. Anthocyanin levels were assessed at 0, 7 and 11 days, respectively, with further valuation by RNA-seq under head-shading and light conditions. RNA sequences were de novo assembled into 50,329 unigenes, of which 38,701 were annotated against four public protein databases. Cluster analysis demonstrated that anthocyanin/phenylpropanoid biosynthesis, photosynthesis, and flavonoid biosynthesis in cluster 8 were the main metabolic pathways regulated by light and had showed associations with flower head growth. A total of 2,400 unigenes showed differential expression between the light and head-shading groups in cluster 8, including 650 co-expressed, 373 specifically expressed under shading conditions and 1,377 specifically expressed under normal light. Digital gene expression (DGE) analysis demonstrated that light perception and the signal transducers CRY3 and HY5 may control anthocyanin accumulation. Following shading, 15 structural genes involved in anthocyanin biosynthesis were downregulated, including PAL, C4H, 4CL, CHS, CHI, F3H and DFR. Moreover, six BoMYB genes (BoMYB6-1, BoMYB6-2, BoMYB6-3, BoMYB6-4, BoMYBL2-1 and BoMYBL2-2) and three BobHLH genes (BoTT8_5-1, BoTT8_5-2 and BoEGL5-3) were critical transcription factors controlling anthocyanin accumulation under light conditions. Based on these data, a light-associated anthocyanin biosynthesis pathway in Broccoli was proposed. This information could help improve broccoli properties, providing novel insights into the molecular mechanisms underpinning light-associated anthocyanin production in purple vegetables.

Keywords: Anthocyanins; Broccoli; Light induction; Transcriptome.

Grants and funding

This work was supported by the National Key R&D Program of China (2017YFD0101805), the Shanghai Agriculture Applied Technology Development Program, China (Grant No. G2016060105), and the Youth Talent Development Plan of Shanghai Municipal Agricultural System, China (Grant No. 20180116). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.