Abstract
Plant U-box armadillo repeat (PUB-ARM) ubiquitin (Ub) ligases have important functions in plant defense through the ubiquitination of target proteins. Defense against pathogens involves vesicle trafficking and the formation of extracellular vesicles. The PUB-ARM protein SENESCENCE ASSOCIATED UBIQUITIN E3 LIGASE1 (SAUL1) can form patches at the plasma membrane related to tethering multi-vesicular bodies (MVBs) to the plasma membrane. We uncovered the structure of a full-length plant ubiquitin ligase and the structural requirements of SAUL1, which are crucial for its function in patch formation. We resolved the structure of SAUL1 monomers by small-angle X-ray scattering (SAXS). The SAUL1 model showed that SAUL1 consists of two domains: a domain containing the N-terminal U-box and armadillo (ARM) repeats and the C-terminal ARM repeat domain, which includes a positively charged groove. We showed that all C-terminal ARM repeats are essential for patch formation and that this function requires arginine residue at position 736. By applying SAXS to polydisperse SAUL1 systems, the oligomerization of SAUL1 is detectable, with SAUL1 tetramers being the most prominent oligomers at higher concentrations. The oligomerization domain consists of the N-terminal U-box and some N-terminal ARM repeats. Deleting the U-box resulted in the promotion of the SAUL1 tethering function. Our findings indicate that structural changes in SAUL1 may be fundamental to its function in forming patches at the plasma membrane.
Highlights
Plants are constantly challenged by pathogen infections
The SENESCENCE ASSOCIATED UBIQUITIN E3 LIGASE1 (SAUL1) ubiquitin ligase can be found in patches at the plasma membrane (PM), and the C-terminal
We resolved the structure of a full-length plant ubiquitin ligase, SAUL1, In this study, resolved the family structure of a full-length plant These ubiquitin ligase, SAUL1, whichwe belongs to the of Plant U-box armadillo repeat (PUB-ARM)
Summary
Plants are constantly challenged by pathogen infections. they evolved specific and sensitive mechanisms for recognizing pathogens to initiate defense responses and can often successfully resist pathogen attacks. Many pathogens have evolved systems that secrete effectors into eukaryotic host cells, aiming to inhibit immune signaling at the level of receptors or downstream signaling components [4,5]. To prevent these effectors from causing disease, plant cells express the second type of immune receptors, nucleotide-binding leucine-rich repeat proteins, which monitor the presence or activity of pathogen effectors in the cytosol to initiate effector-triggered immunity (ETI) [6]. The activation of nucleotide-binding leucine-rich repeat proteins results in a defense program similar to PRR-induced defense mechanisms, but ETI, in contrast to PTI, leads to cell death
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