Dynamics of gene expression associated with anabolism
Biomass as an important process parameter oscillated periodically in
CVEF, indicating that the anabolism of yeast cells may also experience
the changing cycle. Transcriptome analysis showed that a large amount of
genes related to ribosome synthesis were also expressed in a periodic
pattern. As shown in Figure 6, most DEGs of yeast cells at P2 were
up-regulated in comparison with P1, and also in the comparison of gene
expression of yeast cells at P5 to P4, while the DEGs of yeast cells at
P4 were down-regulated compared with P3. However, there was no
significant difference between the gene expression of yeast cells at P2
and P3. Further, the overview of changes in expression of the ribosome
synthesis genes were presented as the non-standard 0π phase pattern that
only decreased in π/2 period, not in the π period. It was indicated that
ribosome synthesis was robust in the 3π/2 period of the oscillation (the
phase from P4, P1, P2 to P3), while much lower in the remaining 1/4
oscillation period (the phase from P3 to P4).
The up-regulated expression of genes related to ribosome synthesis
symbolized the start of anabolism. Thus, it can be speculated that cell
anabolism was initiated at P4, and continued to P3 (P4→P5(P1)→P2→P3, 3/4
oscillation period), while the biomass presented as the π phase pattern
that exist about π phase later than the ribosome synthesis. The
increased expression of ribosomal genes prior to biomass accumulation
indicated that ribosome synthesis was a material preparation process
during the interval of cell division and that the genes related to
ribosome synthesis were prioritized and expressed. In addition, the
periodic change of ribosomal synthesis gene were opposite to the ethanol
concentration, and there was a π phase difference between them, which
may suggest that the regulation of ribosomal synthesis during VHG
oscillation is also related to the ethanol stress.