Abstract
BackgroundSUMO (Small Ubiquitin related Modifier) conjugation is a post translational regulatory process found in all eukaryotes, mediated by SUMO activating enzyme, SUMO conjugating enzyme, and SUMO ligase for the attachment of SUMO to its target protein. Although the mechanism for regulation of SUMO conjugation pathway genes under abiotic stress has been studied to certain extent, the role of SUMO conjugating enzyme in improving abiotic stress tolerance to plant is largely unexplored. Here, we have characterized a SUMO conjugating enzyme gene ‘SaSce9’ from a halophytic grass Spartina alterniflora and investigated its role in imparting abiotic stress tolerance.ResultsSaSce9 gene encodes for a polypeptide of 162 amino acids with a molecular weight of ~18 kD and isoelectric point 8.43. Amino acid sequence comparisons of SaSce9 with its orthologs from other plant species showed high degree (~85-93%) of structural conservation among each other. Complementation analysis using yeast SCE mutant, Ubc9, revealed functional conservation of SaSce9 between yeast and S. alterniflora. SaSce9 transcript was inducible by salinity, drought, cold, and exogenously supplied ABA both in leaves and roots of S. alterniflora. Constitutive overexpression of SaSce9 in Arabidopsis through Agrobacterium mediated transformation improved salinity and drought tolerance of Arabidopsis. SaSce9 overexpressing Arabidopsis plants retained more chlorophyll and proline both under salinity and drought stress. SaSce9 transgenic plants accumulated lower levels of reactive oxygen under salinity stress. Expression analysis of stress responsive genes in SaSce9 Arabidopsis plants revealed the increased expression of antioxidant genes, AtSOD and AtCAT, ion antiporter genes, AtNHX1 and AtSOS1, a gene involved in proline biosynthesis, AtP5CS, and a gene involved in ABA dependent signaling pathway, AtRD22.ConclusionsThese results highlight the prospect of improving abiotic stress tolerance in plants through genetic engineering of the sumoylation pathway. The study provides evidence that the overexpression of SaSce9 in plant can improve salinity and drought stress tolerance by protecting the plant through scavenging of ROS, accumulation of an osmolyte, proline, and expression of stress responsive genes. In addition, this study demonstrates the potential of the halophyte grass S. alterniflora as a reservoir of abiotic stress related genes for crop improvement.
Highlights
SUMO (Small Ubiquitin related Modifier) conjugation is a post translational regulatory process found in all eukaryotes, mediated by SUMO activating enzyme, SUMO conjugating enzyme, and SUMO ligase for the attachment of SUMO to its target protein
Embryo lethality caused by insertional mutation in AtSAE2 or AtSCE1 or double mutations in AtSUMO1 and AtSUMO2 genes of Arabidopsis inferred its role in plant growth and development [17]
SaSce9 of spartina alterniflora is an ortholog of SUMO conjugating enzyme A full length cDNA clone of 489 bp open reading frame, encoding a SUMO conjugating enzyme, named as SaSce9, was obtained from the salt stressed cDNA library of Spartina alterniflora constructed in our laboratory [24]
Summary
SUMO (Small Ubiquitin related Modifier) conjugation is a post translational regulatory process found in all eukaryotes, mediated by SUMO activating enzyme, SUMO conjugating enzyme, and SUMO ligase for the attachment of SUMO to its target protein. Sumoylation or SUMO (Small Ubiquitin related Modifier) conjugation is one of the essential post translational regulatory process essentially found in all eukaryotes It is a three step enzymatic cascade mediated by SUMO activating enzyme (E1 or SAE), SUMO conjugating enzyme (E2 or SCE), and SUMO ligase (E3) for the attachment of SUMO to its target protein [4,5]. Several studies in Arabidopsis highlighted the importance of sumoylation in post translational regulation in response to stresses such as salt, cold, drought, heat, copper toxicity, and nutrient deprivation [14,15,16,17,18]. Detailed understanding of SCE for abiotic stress tolerance in plant is still in its infancy
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