STR3 and CYS3 Contribute to 2‑Furfurylthiol Biosynthesis in Chinese Sesame-Flavored Baijiu Yeast

2-Furfurylthiol is an important aroma compound with characteristic sesame flavor. It was recently identified as the representative aroma compound of Chinese sesame-flavored Baijiu. But its formation mechanism is unclear. In this study, the dominant yeast species <i>Saccharomyces cerevisiae</i>, <i>Pichia kudriavzevii</i>, and <i>Wickerhamomyces anomalus</i> were isolated from samples of Chinese sesame-flavored fermentation and were screened for the capacity of 2-furfurylthiol biosynthesis. Some isolates were found to be capable of generating 2-furfurylthiol using furfural and l-cysteine as precursors, among which <i>S. cerevisiae</i> G20 exhibited the strongest capacity with a yield of 3.03 mg/L. Furthermore, the genes <i>STR3</i> and <i>CYS3</i> from <i>S. cerevisiae</i> were cloned and overexpressed in the reference strain <i>S. cerevisiae</i> S288c and the isolate strain G20, respectively, which resulted in a significant increase in 2-furfurylthiol release in the two strains. Moreover, inactivation of <i>STR3</i> gene in S288c and G20 led to obvious reduction in 2-furfurylthiol production, demonstrating that <i>STR3</i> got involved in 2-furfurylthiol biosynthesis in <i>S. cerevisiae.</i> It is the first time that the yeast isolates with high capacity of 2-furfurylthiol biosynthesis were found during Chinese sesame-flavored Baijiu fermentation and confirmed that the genes <i>STR3</i> and <i>CYS3</i> were closely relevant to 2-furfurylthiol biosynthesis

Summary of annotations for the <i>M</i>. <i>purpureus</i> unigene library.

<p>Summary of annotations for the <i>M</i>. <i>purpureus</i> unigene library.</p

<i>De novo</i> assembly of the <i>M</i>. <i>purpureus</i> transcriptome.

<p><i>De novo</i> assembly of the <i>M</i>. <i>purpureus</i> transcriptome.</p

Target genes and primers for <i>M</i>. <i>purpureus</i>.

<p>Target genes and primers for <i>M</i>. <i>purpureus</i>.</p

Length distribution of the unigene library of <i>M</i>. <i>purpureus</i>.

<p>Length distribution of the unigene library of <i>M</i>. <i>purpureus</i>.</p

Transcript homology of five <i>M</i>. <i>purpureus</i> cultivars and Venn diagram of the number of orthologous transcripts (E-value = 1e^-5).

<p>Venn diagram includes 31 possible intersections between five libraries, and the number of genes shows in each of these overlapping categories. Transcriptome data sets are as follows: COG (light-green color), pfam (light-yellow color), Nr (light-purple color), Uniprot (light-pink color), and Est (light-blue color), the immature embryos.</p

Pathway assignment based on KEGG mapping.

<p>Pathway assignment based on KEGG mapping.</p

Down & up regulated genes of transcription factors and target genes in <i>M</i>. <i>purpureus</i> unigene library.

<p>Down & up regulated genes of transcription factors and target genes in <i>M</i>. <i>purpureus</i> unigene library.</p

Expression of genes related to monacolin K (<i>mokA-mokI</i>) at different phase (2, 5, 8, and 12 days) of <i>M</i>. <i>purpureus</i> M1 and M1-36^*.

<p>Expression of genes related to monacolin K (<i>mokA-mokI</i>) at different phase (2, 5, 8, and 12 days) of <i>M</i>. <i>purpureus</i> M1 and M1-36^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0170149#t005fn001" target="_blank">*</a>}.</p

Monacolin K biosynthetic pathway in <i>M</i>. <i>purpureus</i>.

<p>The red rectangles indicate up-regulated genes including <i>mokE</i> and <i>mokC</i> genes.</p