Abstract
The Arabidopsis thaliana genes PROTEIN INHIBITOR OF ACTIVATED STAT LIKE1 (PIAL1) and PIAL2 encode proteins with SP-RING domains, which occur in many ligases of the small ubiquitin-related modifier (SUMO) conjugation pathway. We show that PIAL1 and PIAL2 function as SUMO ligases capable of SUMO chain formation and require the SUMO-modified SUMO-conjugating enzyme SCE1 for optimal activity. Mutant analysis indicates a role for PIAL1 and 2 in salt stress and osmotic stress responses, whereas under standard conditions, the mutants show close to normal growth. Mutations in PIAL1 and 2 also lead to altered sulfur metabolism. We propose that, together with SUMO chain binding ubiquitin ligases, these enzymes establish a pathway for proteolytic removal of sumoylation substrates.
Highlights
Sumoylation, the conjugation of the small ubiquitin-related modifier (SUMO) to substrate proteins, is an essential posttranslational modification in plants
Two of the Arabidopsis saturating pulse (SP)-RING-containing proteins were characterized in previous work; to complement this, we studied the physiology and biochemistry of the other two proteins
The PIAL2 cDNA was obtained from the RIKEN repository (Seki et al, 2002) and the PROTEIN INHIBITOR OF ACTIVATED STAT LIKE1 (PIAL1) cDNA was isolated by reverse transcription of RNA prepared from plants
Summary
Sumoylation, the conjugation of the small ubiquitin-related modifier (SUMO) to substrate proteins, is an essential posttranslational modification in plants (reviewed in Novatchkova et al, 2004, 2012; Castro et al, 2012; Mazur and van den Burg, 2012; Flotho and Melchior, 2013; Jentsch and Psakhye, 2013; Xu and Yang, 2013). The recent discovery of ubiquitin ligases that bind to SUMO chains (Yin et al, 2012b; Elrouby et al, 2013; Sriramachandran and Dohmen, 2014) suggests that SUMO chains have physiological roles as well. It is currently unclear how widespread SUMO chains really are, how their formation is regulated, and how they influence biological processes in plants
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