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  • sphingosine-1-phosphate The relatively less well studied enc


    The relatively less well-studied encodes the E2 type SUMO-conjugating enzyme. In plants, the SCE family members play roles in abiotic stress responses. An E2 enzyme, SaSce9, from plays roles in salinity and drought stress responses (). Furthermore, SCE can respond to heat stress in rice (). However, the role of in drought stress response in rice has not yet been reported. We previously observed upregulation of an gene transcript in rice during drought stress, simulated by polyethylene glycol 6000 (PEG6000) treatment. Therefore, in this study, we performed the isolation and functional validation of the gene to better understand its role in the drought stress response in rice. MATERIALS AND METHODS
    DISCUSSION SUMOylation mediates covalent attachment of SUMO to target sphingosine-1-phosphate and involves the sequential activities of three key enzymes, E1, E2 and E3, which are SUMO-specific (Park et al., 2011, Castro et al., 2016). The SUMOylation process influences the response of plants against environmental stress including both abiotic stress and biotic stress, such as drought (Catala et al., 2007, Karan and Subudhi, 2012, Miura et al., 2013, Zhang et al., 2013), salt (Karan and Subudhi, 2012, Tomanov et al., 2014), heat (Nigam et al, 2008), low temperature (Miura et al, 2007b), phosphate deficiency (Miura et al, 2005) and pathogen infection (Lee et al., 2006, Xiong and Wang, 2013). SUMOylation involves a three-step enzyme pathway for the attachment of SUMO to its target proteins (Park et al, 2011). The first step is the activation of mature SUMO by a SUMO-specific E1 activating enzyme, which promotes C-terminal binding of SUMO to AMP (SUMO-AMP) in an ATP-dependent reaction. The second step is SUMO conjugation, catalyzed by an E2-conjugating enzyme (SCE1), wherein the activated SUMO is transferred to the cysteine residue of the E2 enzyme by transesterification. In the third step, E2s are subsequently capable of transferring SUMO to a target protein. However, this step can be mediated by SUMO E3 ligases, which greatly enhance the SUMOylation process and promote specificity (Park et al., 2011, Castro et al., 2012, 2016). In this study, a SUMO conjugating enzyme gene OsSCE1 from Nipponbare was isolated to validate its function in relation to the drought stress response in rice. Analysis of the protein sequence derived from the isolated OsSCE1 gene revealed the presence of a highly structural homology with SCE orthologs from other monocots and a dicot (Fig. 1-A). A high degree of similarity was also observed between the SaSce9 gene isolated from grass halophyte (S. alterniflora) and SCE-encoding genes of other monocots, dicots, yeast and amoeba (Karan and Subudhi, 2012). The similarity in SCE-encoding gene expression suggests a functional conserved role for SCE1 across eukaryotes. We also observed ubiquitin conjugating enzyme-like (UBC) domain, a common characteristic of UBC family members, in OsSCE1 protein (Fig. 1-A). This observation was previously reported by Nigam et al (2008) and Chaikam and Karlson (2010). Nigam et al (2008) investigated two SCE-encoding genes, designated OsSCE1 and OsSCE2, based on annotated rice genome entries LOC_Os10g39120 and LOC_Os03g03130, respectively. Moreover, three OsSCE1 genes namely OsSCE1a, OsSCE1b and OsSCE1c from the Rice Annotation Project Database (RAP-DB) were investigated by Chaikam and Karlson (2010). The UBC domain is identified, spanning from 8 to 158 amino acid residues in the SCE1 proteins. Expression of the OsSCE1 gene in WT rice plants under normal condition was detected at relatively high levels in certain tissues (root, leaf blade, leaf sheath and flag leaf), in comparison to expressions in the stem and panicle, which were somewhat lower (Fig. 2-A). Chaikam and Karlson (2010) reported similar expression patterns of OsSCE1a, OsSCE1b and OsSCE1c in root and leaf tissues. In addition, expression of OsSCE1 genes was found to be tissue specific, and the highest expression levels were observed in milk seeds (Chaikam and Karlson, 2010). The presence of the OsSCE1 transcript in all the tested tissues may indicate diverse functions for OsSCE1 in different tissues and stages of rice development.