Metabolite Profiling and Transcriptome Analysis Provide Insight into Seed Coat Color in Brassica juncea

Abstract

The allotetraploid species <i>Brassica juncea</i> (mustard) is grown worldwide as oilseed and vegetable crops; the yellow seed-color trait is particularly important for oilseed crops. Here, to examine the factors affecting seed coat color, we performed a metabolic and transcriptomic analysis of yellow- and dark-seeded <i>B</i>. <i>juncea</i> seeds. In this study, we identified 236 compounds, including 31 phenolic acids, 47 flavonoids, 17 glucosinolates, 38 lipids, 69 other hydroxycinnamic acid compounds, and 34 novel unknown compounds. Of these, 36 compounds (especially epicatechin and its derivatives) accumulated significantly different levels during the development of yellow- and dark-seeded <i>B</i>. <i>juncea</i>. In addition, the transcript levels of <i>BjuDFR</i>, <i>BjuANS</i>,<i>BjuBAN</i>, <i>BjuTT8,</i> and <i>BjuTT19</i> were closely associated with changes to epicatechin and its derivatives during seed development, implicating this pathway in the seed coat color determinant in <i>B</i>. <i>juncea</i>. Furthermore, we found numerous variations of sequences in the <i>TT8</i><i>A</i> genes that may be associated with the stability of seed coat color in <i>B</i>. <i>rapa</i>, <i>B</i>. <i>napus,</i> and <i>B</i>. <i>juncea</i>, which might have undergone functional differentiation during polyploidization in the <i>Brassica</i> species. The results provide valuable information for understanding the accumulation of metabolites in the seed coat color of <i>B</i><i>. juncea</i> and lay a foundation for exploring the underlying mechanism.