Abstract
The tuberous root of Brassica rapa L. (turnip) is an important modified organ for nutrition storage. A better understanding of the molecular mechanisms involved in the process of tuberous root development is of great value in both economic and biological context. In this study, we analyzed the expression profiles of both mRNAs and miRNAs in tuberous roots at an early stage before cortex splitting (ES), cortex splitting stage (CSS), and secondary root thickening stage (RTS) in turnip based on high-throughput sequencing technology. A large number of differentially expressed genes (DEGs) and several differentially expressed miRNAs (DEMs) were identified. Based on the DEG analysis, we propose that metabolism is the dominant pathway in both tuberous root initiation and secondary thickening process. The plant hormone signal transduction pathway may play a predominant role in regulating tuberous root initiation, while the starch and sucrose metabolism may be more important for the secondary thickening process. These hypotheses were partially supported by sequential DEM analyses. Of all DEMs, miR156a, miR157a, and miR172a exhibited relatively high expression levels, and were differentially expressed in both tuberous root initiation and the secondary thickening process with the expression profiles negatively correlated with those of their target genes. Our results suggest that these miRNAs play important roles in tuberous root development in turnips.
Highlights
The modified tuberous root in many vegetables, such as radishes, carrots, turnips, and sweet potatoes provides a great food source for human consumption
Less than 29% of the clean tags for each library could not be aligned to any reference genes due to incomplete sequences, and these tags were designated as unknown tags
Unknown tags and tags mapped to multi-genes were filtered out, and the unique clean tags mapped to a single gene were reserved for further differentially expressed genes (DEGs) analysis
Summary
The modified tuberous root in many vegetables, such as radishes, carrots, turnips, and sweet potatoes provides a great food source for human consumption. Tuberous roots are rich in nutrition and dietary fiber [1], and convenient for storage. Some are of medicinal importance [2,3]. It is important, in the context of economic value, to study the molecular mechanisms underlying the tuberous root formation and development. Since tuberous roots are important modified organs, studies on tuberous root formation and development is of high biological value.
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