Analysis of the metabolome and transcriptome of Brassica carinata seedlings after lithium chloride exposure

Exposure of B. carinata seedlings to increasing concentrations of a non-physiological ion, lithium, showed significant effects on the germination rate, root length, chlorophyll content and fresh weight in brown-seeded and yellow-seeded near-isogenic lines. Metal content analysis and phytochemical profiling indicated that lithium hyper-accumulated and the lipid and phenolic composition dramatically changed in brown-seeded seedlings. Here, sinapic acid esters and chloroplast lipid were replaced by benzoate derivatives, resveratrol and oxylipins after lithium exposure. In contrast, the yellow-seeded plants maintained the same phenolic and lipid composition before and after exposure to lithium and did not tolerate the high metal concentrations tolerated by the brown-seeded line. Microarray analysis using a Brassica napus 15,000 expressed sequence tag (EST) array indicated a total of 89 genes in the brown-seeded line and 95 genes in the yellow-seeded line were differentially expressed more than 20-fold after treatment of B. carinata seedlings with lithium chloride and more than 1083 genes with expression changes greater than 2-fold. The putative functions of the differentially expressed genes included proteins involved in defense, primary metabolism, transcription, transportation, secondary metabolism, cytochrome P450, as well as proteins with unknown functions. Transcriptome changes between yellow-seeded and brown-seeded B. carinata seedlings after lithium chloride exposure indicated that the two lines responded differently to lithium treatment. The expression patterns generally supported the phytochemical data. From the results of this study, B. carinata brown-seeded germplasm showed an ability to survive under moderately high concentrations of lithium chloride (>150 mM). The ability to accumulate this metal ion suggests brown-seeded B. carinata has some potential in phytoremediation of lithium-contaminated water and soil.