Huang et al. demonstrate a novel role–and the underlying mechanism–for FREE1 in regulating LD turnover. Plant Cell. https://doi.org/10.1093/plcell/koac195
Background: Lipid droplets (LDs) are major reservoirs providing energy and lipids for seedling establishment. In vascular plants, the peroxisome-localized lipase SDP1 has been shown to play a major role in modulating LD metabolism, while the retromer and ESCRTIII components play a role in LD metabolism via regulating peroxisomal extension and peroxisomal inner membrane formation, respectively, in Arabidopsis. However, how the peroxisome-localized SDP1 traffics to the LD surface for turnover remains elusive. We previously characterized a plant-unique ESCRT (Endosomal Sorting Complex Required for Transport) component FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING 1 (FREE1) and showed multiple functions in the endomembrane system and autophagy. Here we report a new role of FREE1 in LD turnover.
Question: Depletion of FREE1 led to accumulation of LDs in germinating seedlings with unknown mechanism. This study aims to illustrate the underlying mechanism of FREE1 function in regulating LD turnover.
Findings: We showed that both the formation of SDP1- or PEX11e-positive tubules and the engulfment of LDs by the peroxisomes were impaired in free1 mutants. The degradation of LDs was also impaired in free1 mutants. We further showed that FREE1 interacts specifically with the amphipathic helix (AH) motif of PEX11e and SDP1 to regulate peroxisomal tubulation and SDP1 targeting to the LD surface.
Next steps: Future work should investigate the possible involvements and mechanisms of ESCRT-I and other ESCRT components in regulating peroxisome tubule formation and LD mobilization in plants.
Shuxian Huang, Zhiqi Liu, Wenhan Cao, Hongbo Li, Wenxin Zhang, Yong Cui, Shuai Hu, Mengqian Luo, Ying Zhu, Qiong Zhao, Lijuan Xie, Caiji Gao, Shi Xiao, and Liwen Jiang (2022). The plant ESCRT component FREE1 regulates peroxisome-mediated turnover of lipid droplets in germinating Arabidopsis seedlings. Plant Cell. https://doi.org/10.1093/plcell/koac195