Abstract
In a recent study, it has been shown that biosynthesis of triacylglycerol (TAG) in the oleaginous green alga Chlorella desiccata is preceded by a large increase in acetyl-coenzyme A (Ac-CoA) levels and by upregulation of plastidic pyruvate dehydrogenase (ptPDH). It was proposed that the capacity to accumulate high TAG critically depends on enhanced production of Ac-CoA. In this study, two alternative Ac-CoA producers-plastidic Ac-CoA synthase (ptACS) and ATP citrate lyase (ACL)-are shown to be upregulated prior to TAG accumulation under nitrogen deprivation in the oleaginous species C. desiccata, but not in the moderate TAG accumulators Dunaliella tertiolecta and Chlamydomonas reinhardtii. Measurements of endogenous acetate production and of radiolabelled acetate incorporation into lipids are consistent with the upregulation of ptACS, but suggest that its contribution to the overall TAG biosynthesis is negligible. Induction of ACS and production of endogenous acetate are correlated with activation of alcohol dehydrogenase, suggesting that the upregulation of ptACS is associated with activation of PDH-bypass in C. desiccata. It is proposed that activation of the PDH-bypass in C. desiccata is needed to enable a high rate of lipid biosynthesis under nitrogen deprivation by controlling the level of pyruvate reaching ptPHD and/or mtPDH. This may be an important parameter for massive TAG accumulation in microalgae.
Highlights
Many green algae accumulate, under growth limiting conditions—such as nitrogen deprivation, large quantities of storage products such as starch or triacylglycerol (TAG)
The authors have previously shown that acetyl-coenzyme A (Ac-CoA) is accumulated in response to N deprivation and that this increase could be largely attributed to the rapid induction of plastidic pyruvate dehydrogenase (ptPDH) in a TAG-accumulating alga C. desiccata (Avidan et al, 2015)
It is interesting to assess whether the primary role of the pathway in C. desiccata is to supply Ac-CoA for fatty acids (FA) biosynthesis or alternatively, to support respiration and photosynthesis
Summary
Under growth limiting conditions—such as nitrogen deprivation, large quantities of storage products such as starch or triacylglycerol (TAG). Recent reports have linked between the availability of carbon precursors that can be utilized for fatty acids (FA) biosynthesis—such as acetate or pyruvate—and the rate of TAG accumulation in plants and algae (Goodson et al, 2011; Siaut et al, 2011; Fan et al, 2012; Ramanan et al, 2013; Goodenough et al, 2014), implying that carbon flux is a major determinant controlling the rate of lipid synthesis and accumulation in these. It was suggested that the capacity to accumulate high levels of TAG in algae critically depends on their ability to divert carbon flow towards the synthesis of Ac-CoA following N limitation, consistent with the idea that carbon flux is a major determinant controlling TAG accumulation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
