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. 2011 Jul;34(3):471-8.
doi: 10.1590/S1415-47572011000300018. Epub 2011 Jul 1.

Genetic analysis of D-xylose metabolism by endophytic yeast strains of Rhodotorula graminis and Rhodotorula mucilaginosa

Ping Xu  1 , Renata Bura, Sharon L Doty
Affiliations

Genetic analysis of D-xylose metabolism by endophytic yeast strains of Rhodotorula graminis and Rhodotorula mucilaginosa

Ping Xu et al. Genet Mol Biol. 2011 Jul.

Abstract

Two novel endophytic yeast strains, WP1 and PTD3, isolated from within the stems of poplar (Populus) trees, were genetically characterized with respect to their xylose metabolism genes. These two strains, belonging to the species Rhodotorula graminis and R. mucilaginosa, respectively, utilize both hexose and pentose sugars, including the common plant pentose sugar, D-xylose. The xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) genes were cloned and characterized. The derived amino acid sequences of xylose reductase (XR) and xylose dehydrogenase (XDH) were 32%∼41% homologous to those of Pichia stipitis and Candida. spp., two species known to utilize xylose. The derived XR and XDH sequences of WP1 and PTD3 had higher homology (73% and 69% identity) with each other. WP1 and PTD3 were grown in single sugar and mixed sugar media to analyze the XYL1 and XYL2 gene regulation mechanisms. Our results revealed that for both strains, the gene expression is induced by D-xylose, and that in PTD3 the expression was not repressed by glucose in the presence of xylose.

Keywords: D-xylose metabolism; Rhodotorula graminis; Rhodotorula mucilaginosa; xylitol; xylitol dehydrogenase; xylose reductase.

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Figures

Figure 1
Figure 1
Growth of WP1 and PTD3 (a) in an MS medium, with 3% glucose as the carbon source, (b) in an MS medium with 3% xylose as the carbon source. Baker’s yeast (BK; ATCC6037) was used as positive control. The experiments were carried out in triplicate, the error bars indicating standard deviation.
Figure 2
Figure 2
Exon/intron structures visualization of XR and XDH-encoding-genes of the Rhodotorula graminis WP1 strain.
Figure 3
Figure 3
Exon/intron structures visualization of XR and XDH-encoding-genes of Pichia stipitis.
Figure 4
Figure 4
WP1 and PTD3 XR/XDH gene-expression in cells grown in 2% glucose (lanes 1,4,7,10), 1% glucose+1% xylose (lane 2, 5, 8,11) and 2% xylose (lanes 3,6,9,12). Lanes 1–6: WP1gene expression; Lanes 7–12: PTD3 gene expression.
Figure 5
Figure 5
WP1 and PTD3 XR/XDH gene-expression in cells grown in 2% glucose, 2% xylose and 2% glucose+2% xylose. RNA templates used under different conditions are labeled in the figure.
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