Transcriptomic changes induced by de-activation of lower glycolysis and
its advantage on pentose sugar metabolism in Saccharomyces cerevisiae
Abstract
As a microbial host for cellulosic biofuel production, Saccharomyces
cerevisiae needs to be engineered to express a heterologous xylose
pathway. However, it has been challenging to optimize the engineered
strain for efficient and rapid fermentation of xylose. Deletion of PHO13
(pho13) has been reported to be a crucial genetic perturbation for
improving xylose fermentation. A confirmed mechanism of the
pho13-positive effect on xylose fermentation is that the deletion of
PHO13 transcriptionally activates the genes in the non-oxidative pentose
phosphate pathway (PPP). In the present study, we reported that a
pho13-positive effect was not observed from a couple of engineered
strains, among the many others we have examined. To extend our knowledge
of pho13-mediated metabolic regulation, we performed genome sequencing
of pho13-negative strains. We identified a loss-of-function mutation in
GCR2 responsible for the pho13-negative phenotype. Gcr2 is a
transcriptional activator of the lower glycolytic pathway. Thus, the
deletion of GCR2 (gcr2) led to deactivation of lower glycolysis as
confirmed by RNA-seq. Also, gcr2 resulted in the up-regulation of PPP
genes, which explains the improved xylose fermentation of gcr2 mutants.
As pho13 and gcr2 cause similar transcriptional changes with PPP genes,
there was no synergistic effect between pho13 and gcr2 for improving
xylose fermentation. The present study identified GCR2 as a new knockout
target to improve xylose fermentation and cellulosic biofuel production.