Abstract
Salvia miltiorrhiza Bunge (Labiatae) is an emerging model plant for traditional medicine, and tanshinones are among the pharmacologically active constituents of this plant. Although extensive chemical and pharmaceutical studies of these compounds have been performed, studies on the basic helix-loop-helix (bHLH) transcription factors that regulate tanshinone biosynthesis are limited. In our study, 127 bHLH transcription factor genes were identified in the genome of S. miltiorrhiza, and phylogenetic analysis indicated that these SmbHLHs could be classified into 25 subfamilies. A total of 19 sequencing libraries were constructed for expression pattern analyses using RNA-Seq. Based on gene-specific expression patterns and up-regulated expression patterns in response to MeJA treatment, 7 bHLH genes were revealed as potentially involved in the regulation of tanshinone biosynthesis. Among them, the gene expression of SmbHLH37, SmbHLH74 and SmbHLH92 perfectly matches the accumulation pattern of tanshinone biosynthesis in S. miltiorrhiza. Our results provide a foundation for understanding the molecular basis and regulatory mechanisms of bHLH transcription factors in S. miltiorrhiza.
Highlights
Role of SmMYB39 in the rosmarinic acid pathway has been characterised through overexpression and RNAi-mediated silencing[12]
The number of basic helix-loop-helix (bHLH) genes in S. miltiorrhiza is similar to the number of bHLH genes in A. thaliana, O. sativa, N. tabacum and V. vinifera
A neighbour-joining tree constructed among the 127 bHLH members identified in S. miltiorrhiza indicated a total of 25 distinct subfamilies (Fig. 1), with subfamily A having the largest number of members (20 SmbHLHs) and subfamilies C, L, Q and X the fewest (1 bHLH)
Summary
Role of SmMYB39 in the rosmarinic acid pathway has been characterised through overexpression and RNAi-mediated silencing[12]. An analysis of the S. miltiorrhiza transcriptome revealed 1,341 unigenes belonging to 46 transcription factor families, including 76 unigenes of bHLH transcription factors[13]. Upon treatment with yeast extract and Ag+14, 412 transcription factors (40 bHLH genes) were identified among the differentially expressed genes in S. miltiorrhiza hairy roots. Transcriptome sequencing is not likely to identify all bHLH genes simultaneously, especially those genes expressed under specific conditions. To systematically elucidate the regulatory role of bHLH transcription factors in S. miltiorrhiza, a genome-wide analysis of bHLH transcription factors was performed. Based on various expression patterns and the results of MeJA treatment and qPCR analyses, 3 bHLH genes that likely regulate tanshinone biosynthesis were identified. The findings from this study provide a foundation for understanding the molecular basis and regulatory mechanisms of bHLH transcription factors in S. miltiorrhiza
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