Suppression Subtractive Hybridization Reveals Transcript Profiling of Chlorella under Heterotrophy to Photoautotrophy Transition

Abstract

BackgroundMicroalgae have been extensively investigated and exploited because of their competitive nutritive bioproducts and biofuel production ability. Chlorella are green algae that can grow well heterotrophically and photoautotrophically. Previous studies proved that shifting from heterotrophy to photoautotrophy in light-induced environments causes photooxidative damage as well as distinct physiologic features that lead to dynamic changes in Chlorella intracellular components, which have great potential in algal health food and biofuel production. However, the molecular mechanisms underlying the trophic transition remain unclear.Methodology/Principal FindingsIn this study, suppression subtractive hybridization strategy was employed to screen and characterize genes that are differentially expressed in response to the light-induced shift from heterotrophy to photoautotrophy. Expressed sequence tags (ESTs) were obtained from 770 and 803 randomly selected clones among the forward and reverse libraries, respectively. Sequence analysis identified 544 unique genes in the two libraries. The functional annotation of the assembled unigenes demonstrated that 164 (63.1%) from the forward library and 62 (21.8%) from the reverse showed significant similarities with the sequences in the NCBI non-redundant database. The time-course expression patterns of 38 selected differentially expressed genes further confirmed their responsiveness to a diverse trophic status. The majority of the genes enriched in the subtracted libraries were associated with energy metabolism, amino acid metabolism, protein synthesis, carbohydrate metabolism, and stress defense.Conclusions/SignificanceThe data presented here offer the first insights into the molecular foundation underlying the diverse microalgal trophic niche. In addition, the results can be used as a reference for unraveling candidate genes associated with the transition of Chlorella from heterotrophy to photoautotrophy, which holds great potential for further improving its lipid and nutrient production.

Lipid accumulation and biosynthesis genes response of the oleaginous Chlorella pyrenoidosaunder three nutrition stressors

“…In order to target the genes related to TAG accumulation and learn more about the transcriptional changes in response to nutrient limitation in microalgae, we made an initial effort to search differentially expressed genes using the suppression subtractive hybridization approach under trophic transition: the results indicated that the transition from heterotrophy to photo-induction culture can stimulate lipid accumulation in Chlorella coupled with a series differentially expressed genes in the lipid metabolic pathway [ 42 ].…”

Genomic Foundation of Starch-to-Lipid Switch in Oleaginous Chlorella spp.

“…To model the temporal process featuring the switch of the intracellular metabolite profile from one dominated by starch to one dominated by proteins and lipids, we changed the C. pyrenoidosa cultivation mode from heterotrophy to photoautotrophy at 72 h (Fan et al, 2012a(Fan et al, , 2012bHan et al, 2012), followed by a 48-h light illumination. At each of the six time points during this SHDP process, three biological replicates of separate culture experiments were each sampled for transcriptome analysis via deep mRNA sequencing and metabolite analysis (Fig.…”

“…Remarkably, when cells are shifted from heterotrophic to photoautotrophic conditions, a short duration (1 to 2 d depending on the weather) of illumination induces a prominent change in the intracellular profile, with marked decreases in starch yet 70% to 120% increases in lipids and proteins (Fan et al, 2012a(Fan et al, , 2012bHan et al, 2012;Li et al, 2014b), resulting in both high target product contents (lipids and proteins) and high biomass productivity ( Fig. 1; Supplemental Fig.…”

Comparative Analyses of Three Chlorella Species in Response to Light and Sugar Reveal Distinctive Lipid Accumulation Patterns in the Microalga C. sorokiniana

“…Instead, other Chlorella species have been cultivated under mixo– and heterotrophic conditions for the production of lutein and astaxanthin (antioxidants) and have served as the basis for mathematical models of sugar-based growth [39] – [44] . Recent metabolic flux analyses and transcriptomic studies performed under different trophic conditions also provide compelling information about shifts in Chlorella lipid metabolism [21] , [45] – [47] .…”