Genome-Wide Association Reveals Trait Loci for Seed Glucosinolate Accumulation in Indian Mustard (Brassica juncea L.).

Erwin Tandayu,Ramil Mauleon,Tobias Kretzschmar,Priyakshee Borpatragohain

doi:10.3390/plants11030364

Abstract

Glucosinolates (GSLs) are sulphur- and nitrogen-containing secondary metabolites implicated in the fitness of Brassicaceae and appreciated for their pungency and health-conferring properties. In Indian mustard (Brassica juncea L.), GSL content and composition are seed-quality-determining traits affecting its economic value. Depending on the end use, i.e., condiment or oil, different GSL levels constitute breeding targets. The genetic control of GSL accumulation in Indian mustard, however, is poorly understood, and current knowledge of GSL biosynthesis and regulation is largely based on Arabidopsis thaliana. A genome-wide association study was carried out to dissect the genetic architecture of total GSL content and the content of two major GSLs, sinigrin and gluconapin, in a diverse panel of 158 Indian mustard lines, which broadly grouped into a South Asia cluster and outside-South-Asia cluster. Using 14,125 single-nucleotide polymorphisms (SNPs) as genotyping input, seven distinct significant associations were discovered for total GSL content, eight associations for sinigrin content and 19 for gluconapin. Close homologues of known GSL structural and regulatory genes were identified as candidate genes in proximity to peak SNPs. Our results provide a comprehensive map of the genetic control of GLS biosynthesis in Indian mustard, including priority targets for further investigation and molecular marker development.

Highlights

IntroductionGlucosinolates (GSLs) are a class of well-studied sulphur (S)- and nitrogen (N)- containing secondary metabolites almost exclusively found in Brassicaceae, which include the economically and nutritionally important crops B. napus (canola and rapeseed), B. juncea (Indian mustard), B. oleracea (cabbage) and B. rapa (Chinese cabbage, turnip) [1,2,3]
Glucosinolates (GSLs) are a class of well-studied sulphur (S)- and nitrogen (N)- containing secondary metabolites almost exclusively found in Brassicaceae, which include the economically and nutritionally important crops B. napus, B. juncea (Indian mustard), B. oleracea and B. rapa (Chinese cabbage, turnip) [1,2,3]
An initial filtering for single-nucleotide polymorphisms (SNPs) anchored onto chromosomes for 60% call rate, non-maf filtered and 10% maximum marker heterozygosity resulted in 15,263 SNPs (26% overall with missing SNP calls), and missing states were imputed

Summary

Introduction

Glucosinolates (GSLs) are a class of well-studied sulphur (S)- and nitrogen (N)- containing secondary metabolites almost exclusively found in Brassicaceae, which include the economically and nutritionally important crops B. napus (canola and rapeseed), B. juncea (Indian mustard), B. oleracea (cabbage) and B. rapa (Chinese cabbage, turnip) [1,2,3]. GSLs are categorised into three major classes, depending on the amino acid they are derived from: (i) aliphatic GSLs, predominantly derived from methionine and, to a lesser extent, from leucine, isoleucine and valine; (ii) aromatic GSLs, mostly derived from phenylalanine or tyrosine and (iii) indolic GSLs, derived from tryptophan. A recent comprehensive inventory from the literature and pathway databases (KNApSAcK, KEGG and AraCyc) listed as many as 113 genes associated with GSLs in Arabidopsis that were identified and characterised over the last two decades [4]. This includes 53 biosynthetic genes found in the KEGG or AraCyc databases, 32 experimentally confirmed biosynthetic genes, 23 transcriptional components and five transporters. While the GSL biosynthetic pathways are well understood in Arabidopsis, the respective regulatory and metabolic networks in the allotetraploid Brassica crops (B. napus and B. juncea) are suggested to be much more complex due to their intricate evolutionary history [6]

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