Molecular Mechanisms Of Heme Oxygenase-1 And ABI4 In Mediating Arabidopsis Tolerance Against Salt And Drought Stresses

Plant heme oxygenase(HO)catalyzes the oxygenation of heme to biliverdin,carbon monoxide,and free iron,and is regarded as a stress-responsive protein.Previous studies indicated that the lose of function in HY1 caused salt-hypersensitive phenotypes,while the overexpression of HY1 results in salt tolerance.In vitro studies demonstrated that that HOI and ABI4 involved in ABA-mediated drought stress signaling transduction.However,the physiological function and molecular mechanism of HO1 under salt and drought stress are still unclear.In order to explain BoHO1 improved salt tolerance,and the relationship between HOI and ABI4 in response to drought stress,the pharmacology,genetics and molecular biology methods were used in this study.1.Here,a cabbage HOI gene(named as BoHO1)was isolated and characterized.BoHO1 shares a high degree homology with Arabidopsis AtHO1 and could locate in Arabidopsis chloroplast.BoHO1 mRNA was ubiquitously expressed in cabbage(Brassica oleracea)tissues,and was responsive to several stimuli and chemicals.Genetic evidence illustrated that over-expression of BoHO1 in transgenic Arabidopsis plants significantly alleviated salinity stress-inhibited seedling growth,which were accompanied with the re-establishment of reactive oxygen species and ion homeostasis.Comparative proteomic analysis revealed that protein abundance related to light reactions was greatly suppressed by NaCl stress in wild-type,whereas was partially recovered in BoHO1.Salinity stress also strongly activated stress-related metabolic processes in wild-type,i.e.carbon and energy metabolism,ammonium detoxification,and protein turnover,and these induced tendencies were more intensive in BoHO1.Particularly,proteins related to glutathione metabolism and ion homeostasis were specifically enriched in NaCl-stressed BoHO1.On the basis of above results,we propose that BoHO1 could activate multiple stress-responsive pathways to help Arabidopsis regain cellular homeostasis,thus presenting enhanced adaptation to salinity stress.2.Here we report that the Arabidopsis wide-type,hyl-100,abi4,and rbohD were used in this study.We observed that mutation of HY1 promoted,but over-expression this gene impaired Arabidopsis drought tolerance.This was attributed to the ABA-hypersensitive or-hyposensitive phenotypes,with the regulation of stomatal closure in particularly.However,comparative transcriptomic profile analysis showed that the induction of numerous ABA/stress-dependent genes in dehydrated wild-type plants was differentially impaired in the hy1-100 mutant.In concert,ABA-induced ABI4 transcript accumulation was strengthened in hy1-100 mutant.Genetic analysis further identified that the hy1-associated ABA hypersensitiveness and drought tolerance were arrested in the abi4 background.Moreover,the promotion of ABA-triggered up-regulation of RbohD abundance and reactive oxygen species(ROS)levels in the hy1-00 mutant was almost fully blocked by the mutation of ABI4,suggesting that the HY1-ABI4 signaling in wild-type involved in stomatal closure was dependent on the RbohD-derived ROS production.However,hy1-promoted stomatal closure was not affected by nitric oxide(NO)scavenger.Correspondingly,ABA-insensitive behaviors in rbohD stomata were not affected by either the mutation of HY1 or its ectopic expression in the rbohD background,both of which responded significantly to exogenous ROS.These data indicate that HY1 functioned negatively and acted upstream of ABI4 in drought signaling,which was casually dependent on the RbohD-derived ROS in the regulation of stomatal closure.