Bioconversion of citrus waste into mucic acid by xylose-fermenting Saccharomyces cerevisiae.

Mucic acid holds promise as a platform chemical for bio-based nylon synthesis; however, its biological production encounters challenges including low yield and productivity. In this study, an efficient and high-yield method for mucic acid production was developed by employing genetically engineered Saccharomyces cerevisiae expressing the NAD+-dependent uronate dehydrogenase (udh) gene. To overcome the NAD+ dependency for the conversion of pectin to mucic acid, xylose was utilized as a co-substrate. Through optimization of the udh expression system, the engineered strain achieved a notable output, producing 20 g/L mucic acid with a highest reported productivity of 0.83 g/L-h and a theoretical yield of 0.18 g/g when processing pectin-containing citrus peel waste. These results suggest promising industrial applications for the biological production of mucic acid. Additionally, there is potential to establish a viable bioprocess by harnessing pectin-rich fruit waste alongside xylose-rich cellulosic biomass as raw materials.

The comparisons of expression pattern reveal molecular regulation of fruit metabolites in S. nigrum and S. lycopersicum.

Solanum nigrum, known as black nightshade, is a medicinal plant that contains many beneficial metabolites in its fruit. The molecular mechanisms underlying the synthesis of these metabolites remain uninvestigated due to limited genetic information. Here, we identified 47,470 unigenes of S. nigrum from three different tissues by de novo transcriptome assembly, and 78.4% of these genes were functionally annotated. Moreover, gene ontology (GO) analysis using 18,860 differentially expressed genes (DEGs) revealed tissue-specific gene expression regulation. We compared gene expression patterns between S. nigrum and tomato (S. lycopersicum) in three tissue types. The expression patterns of carotenoid biosynthetic genes were different between the two species. Comparison of the expression patterns of flavonoid biosynthetic genes showed that 9 out of 14 enzyme-coding genes were highly upregulated in the fruit of S. nigrum. Using CRISPR-Cas9-mediated gene editing, we knocked out the R2R3-MYB transcription factor SnAN2 gene, an ortholog of S. lycopersicum ANTHOCYANIN 2. The mutants showed yellow/green fruits, suggesting that SnAN2 plays a major role in anthocyanin synthesis in S. nigrum. This study revealed the connection between gene expression regulation and corresponding phenotypic differences through comparative analysis between two closely related species and provided genetic resources for S. nigrum.

Organellar genome analysis reveals endosymbiotic gene transfers in tomato.

We assembled three complete mitochondrial genomes (mitogenomes), two of Solanum lycopersicum and one of Solanum pennellii, and analyzed their intra- and interspecific variations. The mitogenomes were 423,596-446,257 bp in length. Despite numerous rearrangements between the S. lycopersicum and S. pennellii mitogenomes, over 97% of the mitogenomes were similar to each other. These mitogenomes were compared with plastid and nuclear genomes to investigate genetic material transfers among DNA-containing organelles in tomato. In all mitogenomes, 9,598 bp of plastome sequences were found. Numerous nuclear copies of mitochondrial DNA (NUMTs) and plastid DNA (NUPTs) were observed in the S. lycopersicum and S. pennellii nuclear genomes. Several long organellar DNA fragments were tightly clustered in the nuclear genome; however, the NUMT and NUPT locations differed between the two species. Our results demonstrate the recent occurrence of frequent endosymbiotic gene transfers in tomato genomes.