Rice E3 Ligase-Like Protein OsPIAL1 Positively Regulated the Drought Stress Response but Negatively Regulated the Salt Stress Response

Small ubiquitin-like modifier(SUMO)E3 ligases that facilitate the conjugation of SUMO proteins to target substrates contain an SP-RING domain which is like the RING domain found in ubiquitin E3 ligases.In this study,we isolated and characterized the Oryza sativa protein inhibitor of activated STAT like1(OsPIAL1)containing SP-RING domains,as the rice homolog of Arabidopsis PIALs.OsPIAL1 interacts with OsSUMO proteins but does not interact with rice SUMO-conjugating enzymes(OsSCEs).An analysis of transgenic rice plant shows that OsPIAL1 is involved in SUMO conjugation to SCEs but not in SUMO conjugation to substrates.In addition,this OsPIAL1 activity requires drought stress conditions.Expression profiles show that the OsPIAL1 gene is induced by only drought stress in the leaves,whereas it is repressed by ABA and abiotic stresses in the roots.Salt stress leads to the fastest decrease in OsPIAL1 transcripts in the roots.Furthermore,the stress experiments indicate that the transgenic rice plants overexpressing OsPIAL1 exhibit a drought stress-tolerant phenotype but a salt stress hypersensitive phenotype.Our results and those from Arabidopsis pial mutants suggest that PIALs act as a positive regulator in the drought stress response but as a negative regulator in the salt stress response.