Abstract
Rocket (Eruca sativa) is a source of health-related metabolites called glucosinolates (GSLs) and isothiocyanates (ITCs) but little is known of the genetic and transcriptomic mechanisms responsible for regulating pre and postharvest accumulations. We present the first de novo reference genome assembly and annotation, with ontogenic and postharvest transcriptome data relating to sulfur assimilation, transport, and utilization. Diverse gene expression patterns related to sulfur metabolism, GSL biosynthesis, and glutathione biosynthesis are present between inbred lines of rocket. A clear pattern of differential expression determines GSL abundance and the formation of hydrolysis products. One breeding line sustained GSL accumulation and hydrolysis product formation throughout storage. Multiple copies of MYB28, SLIM1, SDI1, and ESM1 have increased and differential expression postharvest, and are associated with GSLs and hydrolysis product formation. Two glucosinolate transporter gene (GTR2) copies were found to be associated with increased GSL accumulations in leaves. Monosaccharides (which are essential for primary metabolism and GSL biosynthesis, and contribute to the taste of rocket) were also quantified in leaves, with glucose concentrations significantly correlated with the expression of numerous GSL-related genes. Significant negative correlations were observed between the expression of glutathione synthetase (GSH) genes and those involved in GSL metabolism. Breeding line “B” showed increased GSH gene expression and low GSL content compared to two other lines where the opposite was observed. Co-expression analysis revealed senescence (SEN1) and oxidative stress-related (OXS3) genes have higher expression in line B, suggesting that postharvest deterioration is associated with low GSL concentrations.
Highlights
Sulfur (S) is a critical macronutrient that plants require for growth and development (Kopriva et al, 2016)
We present a de novo E. sativa reference genome sequence, and report on the specific effects harvest, wash treatment, and postharvest storage have on GSL biosynthesis and sulfur metabolism gene expression through RNA sequencing (RNAseq) in three elite inbred lines
Elite breeding line C was assembled into 49,933 contigs (≥500 bp)
Summary
Sulfur (S) is a critical macronutrient that plants require for growth and development (Kopriva et al, 2016). GSLs are found in the leafy vegetable Eruca sativa (“salad” rocket), which has gained significant popularity amongst consumers over the last 10 years (Bell and Wagstaff, 2014). GSLs themselves are not bioactive, and are hydrolyzed by myrosinase enzymes (β-thioglucoside glucohydrolase; TGG) when tissue damage takes place. They form numerous breakdown products including isothiocyanates (ITCs; Wittstock and Burow, 2010), which are of foremost interest for their anticarcinogenic effects in humans (Satyan et al, 2006). The retention of GSLs in the postharvest storage period of rocket is of critical importance for maximizing the potential health benefits for consumers (Martinez-Sanchez et al, 2006)
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