The Functions Of MAPRs And Pollen Ole E 1 Under Endoplasmic Reticulum Stress In Arabidopsis Thaliana

The maintenance of intracellular homeostasis is critical to plant survival under adverse conditions,and the homeostasis of the endoplasmic reticulum can be affected by various stress resulting in ER stress.Once ER stress occurs,unfolded protein response(UPR)will be initiated to alleviate the damage and help the plant resume growth.At present,little is known about the key factors regulating ER stress resistance and the relationship between ER stress regulation and hormone signaling pathways or environmental signals in plants.In Arabidopsis thaliana,Golgi anti-apoptotic proteins(GAAPs)resist cell death upon ER stress and are negative regulators of the UPR MAPR3(Membrane-associated progesterone receptor 3)and POLE1(Pollen Ole e 1)are characterized as interactors of GAAPs by our group.MAPR3 plays positive role against ER stress by interacting with GAAPs.It has been reported that the protein MAPR5,which is highly homologous to MAPR3,is a negative regulator of BR(Brassinolide)signaling pathway.However,there are some questions as follows.What is the effect of the interaction between MAPR3 and GAAPs on the BR signaling pathway?How is the interaction between the function of MAPR3 and GAAPs in resisting to ER stress and their function in the BR signal pathway?What is the relationship between ER stress regulation pathway and light or dark signals?What is the function of POLEs in ER stress.In this study,single mutants of MAPRs,double mutants of MAPR3 and BRI1 and multiple mutants of MAPR3 and GAAPs were used to analyze the functions and regulatory mechanisms of MAPR3 and GAAPs in BR signaling pathway and ER stress.Single mutants of POLEs and double mutants of POLE1 and GAAP 1/GAAP3 were used to analyze the function of POLEs under ER stress.The main findings are as follows1.The results of the phenotype and the sensitivity of mutants to eBL(epi-Brassinolide)or Brz(Brassinazole)analysis showed that the mutation of MAPR3 restores the growth defect phenotype of BRI1 mutants partially.And the results of the promotion of hypocotyl elongation by exogenous eBL indicated that MAPR3 and GAAP3 coordinately negatively regulated the BR signaling pathway,while GAAP1,GAAP2 and GAAP4 were positive regulators which antagonized the function of MAPR32.The analysis of mutants' sensitivity to high temperature and IAA showed that the mutation of MAPR3 enhanced the promotion of hypocotyl elongation by high temperature and also enhanced the sensitivity of hypocotyl to IAA,but decreased the sensitivity to IAA in roots.The results indicated that MAPR3 was a negative regulator in hypocotyl,while it played a positive role in root in regulating the response to IAA GAAP2 antagonized MAPR3 function in the hypocotyls and played a positive regulatory role in IAA perception.GAAP2 and MAPR3 synergistically promote the perception of IAA in root.The results of gravitropism analysis of the mutant also indicated that MAPR3 was involved in regulating BR and IAA signal responses.The subcellular location analysis showed that MAPR3 was located in endometrial systems like endoplasmic reticulum,cytoplasm and intracellular bodies3.The results of ER stress sensitivity experiment under light and dark conditions showed that the resistance of plants to ER stress was increased under dark conditions compared to light conditions.The function of GAAP1-GAAP3 and MAPR3 positively regulated the resistance to ER stress depended on light signals.And the function of MAPR3 under light also depended on BRI1 or was antagonized by BRI1.Under dark condition,GAAP1-GAAP3,GAAP1 and MAPR3 co-negatively regulated ER stress resistance in plants,while BRI1 mainly played as a negative regulator to the resistance of ER stress in dark.In terms of the induction of ROS,BRI1 only had inhibitory effect under light condition,and had no obvious effect on ER stress under dark condition MAPR3 has the same effect as BRI1 under light condition and inhibited the production of ROS,while MAPR3 enhanced the production of ROS under dark condition,which will be antagonized by BRI1.4.qRT-PCR was conducted to detect the expression levels of circadian clock-related genes and UPR pathway-related genes under different light conditions.The mutations ofMAPR3 and GAAP1 changed the expression levels and expression patterns of circadian clock-related genes under different light conditions,and the expression levels of Bip3 and bZip60s were affected by the circadian clock5.Morphological and cytological experiments were performed to analyze membrane permeability and ROS levels under ER stress.The results showed that POLE1 and POLE2 can inhibit cell damage induced by ER stressIn summary,MAPR3,as an interactor of GAAPs,played a negative role in the BR signaling pathway,while GAAPs played a positive role.The two type proteins were also involved in the perception of auxin,in which they had different roles in the ground and underground parts.They also played a role in the regulation of ER stress resistance The interaction between MAPR3 and GAAPs against ER stress was affected by the BR signaling pathway,and also influenced by the circadian clock.The expression of POLE1,another interaction factor of GAAPs,and its homologous protein POLE2 positively regulated the resistance to ER stress.In order to help people more fully understand the response of plants to abiotic stress and know the relationship between plant hormones and plant stress resistance,to provide a basis for improving the survival rate of plants in adversity,how MAPRs,POLEs and GAAPs regulate the resistance under ER stress and what is the relationship between ER stress regulation and hormone pathways need to be further addressed.