Protein Ubiquitination and Sumoylation in ABA Signaling - Abscisic Acid: Metabolism, Transport and Signaling - page 173

Fig. 9.1 The three-
dimensional structure of
UBQ 14 (AT4G02890) and
SUMO 1 (AT4G26840) is
predicted at the Web site
http://swissmodel.expasy.org

UBQ 14 SUMO 1

GG

GG

SUMO genes were processed by ubiquitin-like SUMO-specific proteases (ULP)
that delete about 10 amino acids directly after C terminus diglycine (GG) motif,
leaving diglycine residues in mature SUMO proteins (Colby et al. 2006 ). Plant
ULP also possesses isopeptidase activity to recycle SUMO from substrates, indi-
cating sumoylation is a kind of reversible post-translational modification.
Similar to ubiquitination process, sumoylation of substrate involves sequen-
tial catalytic reaction by a cascade of enzymes: SUMO E1 activating enzyme,
SUMO E2 conjugating enzyme, and SUMO E3 ligase. In Arabidopsis, SUMO
E1, a heterodimer SAE1/SAE2 (different from ubiquitination with a single
E1), activates sumoylation primarily and subsequently transfer SUMO through
a thioester linkage from a catalytic cysteine residue in E1 to the single known
SUMO-conjugating E2 (SCE1). Whereas more than 1,500 ubiquitin E3s (or
complexes) were identified, up to now only two SUMO E3 ligases were identi-
fied in Arabidopsis, AtSIZ1 and HPY2/AtMMS21, which facilitate the transfer
of SUMO from SUMO E2-conjugating enzyme to substrate protein (Miura and
Hasegawa 2010 ). A covalent bond linkage occurs between diglycine of SUMO
and ʵ amino group of lysine residue located in a conserved sumoylation motif
ˈ KXE/D ( ˈ , an aliphatic residue, preferably L, I or V; X, any amino acid).
Mostly from yeast and mammalian, it has been shown that sumoylation con-
trolled a broad of cellular activities, including roles in gene expression, main-
tenance of chromatin integrity, signal transduction, protein trafficking, and
stabilizing proteins by protecting them from ubiquitination-dependent protein
degradation.
Proteomic and genetic analysis mainly in Arabidopsis highlight the importance
of ubiquitination and sumoylation action to control the key factors during hor-
mone synthesis, perception, and downstream signaling in the most plant hormone
signaling, including auxin, ABA, brassinosteroid (BR), cytokinin, ethylene (ET),
gibberellins (GA), jasmonic acid (JA), salicylic acid (SA), strigolactone (SL), and
zeatin. Here, we summarize the current knowledge on the protein ubiquitination
and sumoylation in ABA signaling in the plants.