Molecular Mechanisms Of Arabidopsis SUMO-specific Protease Genes EL5 And EL6 Regulating Plant Fertility

Sumoylation is a crucial reversible post-translational modification of protein which involved in extensive cellular processes in different eukaryotic organisms.SUMO protease serves as a key balancer to regulate the SUMOylation level in organ ism.The previously indentified SUMO proteases were reported to be implicated in flowering,SA synthesis and positive response to salt stress.Previously in our lab,we cloned two genes named as EL5 (ESD4-like 5) and EL6 from Arabidopsis genome and indentified their SUMO protease activities.We obtained T-DNA null mutants el5-1(semisterile) and el6-2(wild type-like) and the el5-1 el6-1 double mutant which displayed severe sterile phenotype due to defects in flower structure,gametogenesis and embryogenesis. EL5 played a significant role, while EL6 had a minor role in affecting the reproductive process.However,the molecular mechanism of EL5,EL6 regulating the reproductive growth remains unknown.Further analysis of CYCB1 accumulation and cell fate specification marker genes expression pattern in mature pollen grains and embryo sacs from el5-1 el6-2 shows CYCB1 improperly accumulated in embryo sac which likely caused mitosis defect and lost/alter the normal fate specification feature of nuclei and cells. Though CYCB1 did not accumulate in mature pollens from mutant, the cell fate specification feature of nuclei and cells was also altered.We screen out a putative target EDA9 (a 3-Phosphoglycerate Dehydrogenase which involved in embryogenenis and male gametogenesis) interacting with both EL5 and SUMO1. Meanwhile,we also screened out 15 putative targets associated with reproductive growth which interacting with both EL6 and SUMO1.We isolated two novel Arabidopsis ULP1b encoded genes ULP1b(341aa) and ULP1b(309aa) likely derived from two different splicing manners. The both proteins mainly localized in the cell nucleolus and neither interacted with SUMO1.