Biomedical Engineering Reference
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traits or slowing down trait degeneration in microalgal feedstock development and
preservation.
(3) Strategies and tools for validation of gene function. Even for the widely
studied C. reinhardtii, nearly 40% of the protein-coding sequences on its genome
remain functionally unknown. One functional characterization strategy is via the
integration of the genome, transcriptome, proteome and metabolome tools. For
example, almost immediately upon completion of the O. tauri genome, proteins
were identified that play roles in key biological processes such as photosynthesis,
photoperiod, flagella assembly, cellular lipid accumulation under nitrogen star-
vation etc. [
27
], and were functionally validated by gene manipulations [
28
].
Another approach in testing gene function builds upon small RNA profiling. In
Chlamydomonas, small RNA interference was used to specifically knock-down the
expression of major lipid droplet protein (MLDP) whose down-regulation
enhanced the volume of cellular lipid-droplet under nitrogen starvation. This
demonstrates the potential of genetic engineering, e.g. small RNA interference, on
breeding/selection of oleaginous microalgae [
27
,
29
,
30
], even though the total
lipid content of the engineered strain is still far lower than that required by large-
scale biofuel production. The genetic apparatuses for small RNAs functioning are
present in Nannochloropsis, indicating the possibility of a microRNA-based gene-
specific knock-down tool to further improve key traits for biofuel production.
(4) Targets and approaches of genetic engineering. For example, in O. tauri,26
selenocysteine-containing proteins were identified while only 10 were found in
Chlamydomonas, whose genome size is almost ten times larger, suggesting the
importance of micronutrients in their ecological strategies and speciation [
21
].
Over-represented genes involved in polyamine metabolism in T. pseudonana
indicated significant roles of long-chain polyamines in silica nanofabrication. In
oleaginous microalgae such as Nannochloropsis, lipid accumulation is induced by
a number of stress conditions that include nitrogen depletion and exposure to high
light intensity. Reconstructed gene co-expression networks and other molecular
phenotype data in response to each of these environmental stimuli and their
combinations should allow the intricate interactions among the different functional
modules to be delineated, thus narrowing down the potential targets of genetic
engineering to a prioritized list of key metabolic or regulatory junctions.
Furthermore, the integrated network should allow probing the nature of regulation;
for example, does the regulation occur at genome, transcriptional, post-tran-
scriptional or post-translational levels?
6 Coupling Feedstock Development with Downstream
Processing
In addition to feedstock development, several crucial research gaps must be
overcome in order to achieve a full-scale operation. A comprehensive research
portfolio should include: (1) a high throughput algal strain selection method and
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