Zhao et al. identify RESURRECTION 1 as a suppressor of free1 that negatively regulates endomembrane trafficking.
Plant Cell https://doi.org/10.1105/tpc.19.00003
By Qiong Zhao
The Chinese University of Hong Kong
Background: Plants have an evolutionarily conserved endomembrane system, which includes the endoplasmic reticulum, Golgi apparatus, nuclear envelope, endosomes, multivesicular bodies (MVBs), and vacuoles. MVBs are unique membrane-bound organelles that contain in their lumen smaller vesicles derived from their outer membrane through inward budding. The sorting and packaging of ubiquitinated membrane proteins into MVBs are facilitated by a set of protein complexes named the Endosomal Sorting Complex Required for Transport (ESCRT) machinery in eukaryotic cells. Plants regulate membrane protein homeostasis through the MVB-mediated endomembrane trafficking system. FREE1, a unique ESCRT component in plants, is essential for MVB and vacuole biogenesis and has multiple functions.
Question: We aimed to determine how FREE1 performs multiple functions in plants and whether other players work co-ordinately with FREE1.
Findings: Through a forward genetic suppressor screen, we identified RST1 (RESURRECTION 1) as a suppressor of free1 that negatively regulates the endomembrane trafficking pathway, in the model plant Arabidopsis. Depletion of FREE1 causes significant accumulation of RST1, and transgenic Arabidopsis plants over-expressing RST1 display retarded seedling growth with dilated MVBs, and inhibition of endocytosed FM4-64 dye to the tonoplast. In addition, endocytic degradation of membrane vacuolar cargoes is enhanced in the rst1 mutant. Thus, RST1 is a novel negative regulator of membrane protein homeostasis regulators. Furthermore, we reveal a coordinated positive and negative regulatory mechanism that maintains MVB-mediated membrane protein homeostasis.
Next steps: As this study does not provide direct evidence of how the cytosolic RST1 performs its molecular function and how RST1 associates with membrane, these topics will be our next major research focus. At the molecular level, RST1 may directly interact with yet-to-be-identified key components in the cytosol to prevent their function at the membrane.
Qiong Zhao, Jinbo Shen, Caiji Gao, Yong Cui, Yongyi Wang, Jie Cui, Lixin Cheng, Wenhan Cao, Ying Zhu, Shuxian Huang, Qianzi Zhou, Cheuk Ka Leong, King Pong Leung, Xuemei Chen and Liwen Jiang (2019). RST1 is a FREE1 Suppressor that Negatively Regulates Vacuolar Trafficking in Arabidopsis. Plant Cell; DOI: https://doi.org/10.1105/tpc.19.00003
Key words: FREE1, vacuolar trafficking, RST1, suppressor screen