Abstract
In eukaryotic cells, lipids in the form of triacylglycerols (TAGs) are the major reservoir of cellular carbon and energy. These TAGs are packed into specialized organelles called lipid droplets (LDs). They can be found in most, if not all, types of cells, from bacteria to human. Recent data suggest that rather than being simple storage organelles, LDs are very dynamic structures at the center of cellular metabolism. This is also true in plants and algae, where LDs have been implicated in many processes including energy supply; membrane structure, function, trafficking; and signal transduction. Plant and algal LDs also play a vital role in human life, providing multiple sources of food and fuel. Thus, a lot of attention has been paid to metabolism and function of these organelles in recent years. This review summarizes the most recent advances on LDs degradation as a key process for TAGs release. While the initial knowledge on this process came from studies in oilseeds, the findings of the last decade revealed high complexity and specific mechanisms of LDs degradation in plants and algae. This includes identification of numerous novel proteins associated with LDs as well as a prominent role for autophagy in this process. This review outlines, systemizes, and discusses the most current data on LDs catabolism in plants and algae.
Highlights
Lipids in plants and algae can be generally divided into two major groups, storage lipids and membrane lipids
Mutation in OsATG7 was associated with a lower number of lipid droplets (LDs) in mature pollen and a higher accumulation of LDs in tapetal cells compared to wild type plants. These results, together with the observation that in wild type plants LDs were enclosed in the vacuoles of rice tapetal cells, suggest that ATG7-dependent tapetal autophagy may be responsible for LDs degradation and lipid metabolism in the tapetum (Kurusu et al, 2014)
The findings described by Fan et al (2019) showed that microlipophagy observed in Arabidopsis leaves depends on core components of macroautophagy pathway, as has been described previously in yeast
Summary
Lipids in plants and algae can be generally divided into two major groups, storage lipids and membrane lipids. Overexpression of both these proteins in P. tricornutum was correlated with increased TAGs content and enlarged LDs during N deprivation (Yoneda et al, 2016; Wang et al, 2017), suggesting their analogous role to plant oleosin. TAG lipases play one of the most essential roles in LDs degradation in plants and algae.
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