Comparative transcriptomic analysis of seed coats with high and low lignin contents reveals lignin and flavonoid biosynthesis in Brassica napus

Yiran Ding,Liezhao Liu,Cunmin Qu,Maoteng Li,Jia Wang,Shizhou Yu,Jiana Li

doi:10.1186/s12870-021-03030-5

Abstract

BackgroundBrassica napus L. (2n = 38, AACC) is one of the most important oil crops and sources of protein for animal feed worldwide. Lignin is a large molecule aromatic polymer and a major cell wall component. However, lignin in the seed coat reduces the availability and restricts the development of rapeseed cake. Therefore, it is critical to reduce the lignin content of the seed coat. Here, high-lignin (H-lignin) and low-lignin (L-lignin) content recombinant inbred lines (RILs) were selected from an RIL population for analysis.ResultsThe cross-section results indicated that the seed coat of the H-lignin lines was thicker than that of the L-lignin lines, especially the palisade layer. The seed coats and embryos at 35, 40 and 46 days after flowering (DAF) were subjected to RNA sequencing (RNA-Seq), and the expression of the BnPAL and BnC4H gene families in the lignin pathway was significantly higher in the H-lignin seed coat than in the L-lignin seed coat. The Bn4CL gene family also showed this trend. In addition, among the genes related to plant hormone synthesis, BnaC02g01710D was upregulated and BnaA07g11700D and BnaC09g00190D were downregulated in H-lignin lines. Some transcription factors were upregulated, such as BnNAC080, BnNAC083, BnMYB9, BnMYB9-1, BnMYB60 and BnMYB60-1, while BnMYB91 was downregulated in H-lignin lines. Moreover, most genes of the flavonoid pathway, such as BnCHS and BnDFR, were strongly expressed in H-lignin seed coat.ConclusionsIn Our study, some key genes such as hormone synthesis genes, transcription factors and miRNAs related to lignin and flavonoid biosynthesis were identified. A regulatory model of B. napus seed coat lignin was proposed. These results provide new insight into lignin and flavonoid biosynthesis in B. napus.

Highlights

Brassica napus L. (2n = 38, AACC) is one of the most important oil crops and sources of protein for animal feed worldwide
It was proven that a reduction in L-Phenylalanine ammonia-lyase (PAL) activity resulted in a decrease in lignin content [9]
Screening and quality trait analysis of H‐ and L‐lignin lines Seeds of 172 recombinant inbred lines (RILs) of B. napus were harvested in May 2014 and May 2015 and scanned by a near-infrared rapid quality analyser

Summary

Introduction

It is critical to reduce the lignin content of the seed coat. Genes encoding the key enzymes in lignin synthesis have been cloned and functionally studied by a large number of researchers with the ultimate goal of altering the content or composition of lignin in plants. The lignin content of transgenic poplar (Populus tremuloides Michx.) and Arabidopsis lines were reduced when 4-coumarate: CoA ligase (4CL) expression was downregulated, and the G- and S-type lignin monomer ratio was reduced [11,12,13]. Many studies have been conducted on related topics, the molecular mechanisms of this phenotype remain unclear due to the genomic complexity of B. napus and the influence of other factors on the rapeseed seed coat [29, 30]

Methods

Results

Discussion

Conclusion