Insights into glucosinolate accumulation and metabolic pathways in Isatis indigotica Fort.

Shu Yang,Miaomiao Qin,Rui Liu,Yuanyuan Wang,Xiangyang Hu,Jinyu Zheng,Tianyi Zhang,Tao Li,Zirong Wang,Tian’E Gao

doi:10.1186/s12870-022-03455-6

Abstract

BackgroundGlucosinolates (GSLs) play important roles in defending against exogenous damage and regulating physiological activities in plants. However, GSL accumulation patterns and molecular regulation mechanisms are largely unknown in Isatis indigotica Fort.ResultsTen GSLs were identified in I. indigotica, and the dominant GSLs were epiprogoitrin (EPI) and indole-3-methyl GSL (I3M), followed by progoitrin (PRO) and gluconapin (GNA). The total GSL content was highest (over 20 μmol/g) in reproductive organs, lowest (less than 1.0 μmol/g) in mature organs, and medium in fresh leaves (2.6 μmol/g) and stems (1.5 μmol/g). In the seed germination process, the total GSL content decreased from 27.2 μmol/g (of seeds) to 2.7 μmol/g (on the 120th day) and then increased to 4.0 μmol/g (180th day). However, the content of indole GSL increased rapidly in the first week after germination and fluctuated between 1.13 μmol/g (28th day) and 2.82 μmol/g (150th day). Under the different elicitor treatments, the total GSL content increased significantly, ranging from 2.9-fold (mechanical damage, 3 h) to 10.7-fold (MeJA, 6 h). Moreover, 132 genes were involved in GSL metabolic pathways. Among them, no homologs of AtCYP79F2 and AtMAM3 were identified, leading to a distinctive GSL profile in I. indigotica. Furthermore, most genes involved in the GSL metabolic pathway were derived from tandem duplication, followed by dispersed duplication and segmental duplication. Purifying selection was observed, although some genes underwent relaxed selection. In addition, three tandem-arrayed GSL-OH genes showed different expression patterns, suggesting possible subfunctionalization during evolution.ConclusionsTen different GSLs with their accumulation patterns and 132 genes involved in the GSL metabolic pathway were explored, which laid a foundation for the study of GSL metabolism and regulatory mechanisms in I. indigotica.

Highlights

Glucosinolates (GSLs) play important roles in defending against exogenous damage and regulating physiological activities in plants
The results revealed that Methyl jasmonate (MeJA), NaCl and ABA had the most remarkable effects on the total GSL accumulations, and the peak contents were 3.85 (10.7-fold compared to control groups, 6 h), 2.96 (7.7-fold, 3 h) and 3.32 μmol/g (8.9-fold, 24 h), respectively
Both of these results suggest that more aliphatic GSLs and fewer aromatic and (See figure on page.) Fig. 3 Chromosome locations of GSL metabolism genes. a Numbers on the left show the location (Mb) of genes on pseudochromosomes; Arrows on the right are the relative direction; Genes with gradient green rectangle background represent side-chain elongation process, core structure formation process, side-chain modification process and co-substrate process, respectively; Light red rectangles represent myrosinases, and dark red shapes represent co-factor; Yellow rectangles mean transcription factors; Similar sequences of biosynthetic genes and breakdown genes are filled with light and dark grey, respectively; Boxes of transportation genes are painted with blue; Segments filled in orange on the pseudochromosome are enlarged in b

Summary

Introduction

Glucosinolates (GSLs) play important roles in defending against exogenous damage and regulating physiological activities in plants. GSL accumulation patterns and molecular regulation mechanisms are largely unknown in Isatis indigotica Fort. Isatis indigotica Fort., belonging to Brassicaceae, is widely used in the food, pharmaceutical and cosmetics industries, and its dried leaves and roots, named “Da Qing Ye” and “Ban Lan Gen”, have been proven to have antiviral and antifungal effects and to activate the immune system [1, 2]. There are numerous compounds in I. indigotica, such as indole alkaloids, lignan metabolites, radix isatidis polysaccharides and glucosinolates. Glucosinolates (GSLs), known as secondary metabolites in plants, are widely distributed in over 3000 species in 16 families, and are well studied in Arabidopsis thaliana [7].

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