SUMO proteases: uncovering the roles of deSUMOylation in plants

Abstract

Plants have evolved to cope with changing environmental conditions. One way plants achieve this is through post-translational modification of target proteins by ubiquitination and SUMOylation. These post-translational modifiers (PMs) can alter stability, protein-protein interactions, and the overall fate of the protein. Both of these systems have remarkable similarities in terms of the process leading to attachment of the PM to its substrate : having to undertake activation, conjugation, and finally ligation to the target. In the ubiquitin system, there are a vast number of ubiquitin ligase enzymes (E3s) that provide specificity for the attachment of ubiquitin. With the SUMO system, only a small number of SUMO E3 ligases have so far been identified in the fully sequenced plant genomes. In Arabidopsis thaliana, there are only two SUMO E3s, compared to over 1400 ubiquitin E3s, a trend also observed in crop species such as Oryza sativa and Zea mays Recent research indicates that removing SUMO from its substrate by the enzymatically active SUMO proteases is a vital part of this system. A class of SUMO proteases called ubiquitin-like proteases (ULPs) are widespread in all eukaryotes; within plants, both monocot and dicot kingdoms have conserved and divergent ULPs and ULP-like proteases. This paper examines the roles ULPs have in stress responses and highlights the 'fine-tuning' of SUMO attachment/removal in balancing growth versus stress.

Exploiting protein modification systems to boost crop productivity: SUMO proteases in focus

“…3), but a number of novel groups also emerge, as was previously suggested (Yates et al , 2016). Meanwhile, the ULP2 group is less clearly defined in cereals.…”

“…More fundamentally, the plant must reliably produce viable seed and enough vegetative growth to sustain the development of many and/or large seeds. A number of these aspects have already been linked to (de)SUMOylation, notably fecundity, germination time, seed development, and stress tolerance (Lois et al , 2003; Novatchkova et al , 2004; Saracco et al , 2007; van den Burg et al , 2010; Augustine et al , 2016; Yates et al , 2016). …”

“…A consensus group of seven ULPs has been identified in Arabidopsis, of which six have been characterized (Murtas et al , 2003; Novatchkova et al , 2004; Conti et al , 2008; Hermkes et al , 2011; Kong et al , 2017; Liu et al , 2017). The observation that substantially more ULPs than E3 ligases are present in Arabidopsis has led to the hypothesis that specificity in the SUMO system may also be conferred by deSUMOylation (Yates et al , 2016). In order to investigate whether this pattern holds true in crops and whether the cultivation level influences the number of ULPs present, we compare the number of putative ULP SUMO proteases in crop plants and their non-crop relatives.…”

Revised nomenclature and functional overview of the ULP gene family of plant deSUMOylating proteases

“…Like ubiquitin (Ub), SUMO acts in the post-translational modification of proteins, and is important for plant development and adaptive responses to the environment (Castro et al , 2012; Yates et al , 2016). The SUMO conjugation and deconjugation cycles have to be tightly regulated, and numerous SUMO proteases are fundamental for this equilibrium.…”

Arabidopsis thaliana SPF1 and SPF2 are nuclear-located ULP2-like SUMO proteases that act downstream of SIZ1 in plant development

“…After the imposition of stress, SUMO conjugates slowly diminish by the action of ULPs. ULPs are fundamental players in the fine-tuning of the SUMO conjugation/deconjugation levels and, consequently, are essential to balance plant growth and stress responses (Conti et al , 2014; Yates et al , 2016). On the other hand, knowledge regarding the importance and functions of SUMO proteases in plant physiology is very limited and many ULPs are yet to be extensively characterized.…”