Drought Resistance And Its Signal Transduction Were Regulated By Molybdenum In Winter Wheat

Molybdenum(Mo)is an essential trace element for plants,which is involved in carbon,nitrogen,sulfur and hormone metabolisms by Mo-enzymes,it thus plays a significant role in plant growth.The Mo-enzymes aldehyde oxidase(AO)and nitrate reductase(NR)are involved in abscisic acid(ABA)and nitric oxide(NO)synthesis respectively,which have important roles in the regulation of drought tolerance in plants.Therefore,this study is premised on the effects of Mo on drought resistance in wheat,and based on the mainline of signal transduction regulated by Mo-enzymes AO and NR,uncovering the physiological and molecular mechanisms by which Mo improves drought tolerance in wheat.The main results are as follows:1)It is confirmed that Mo application can improve the drought resistance of wheat.The results showed that Mo application increased dry biomass and grain yield due to improvement of photosythesis in two cultivars of wheat under drought stress,and the yield increased rates of wheat by applying Mo under drought conditions were more than those under non-drought conditions.Supplemental Mo decreased water loss as result of the decreases of stomatal conductance(Gs)and transpiration rate(Tr),and then increased the relative water contents,eventually improved the water use efficiency of wheat leaf under polyethylene glycol 6000 simulated drought stress(PSD).The ability of reactive oxygen species scavenging were improved by Mo-increased antioxidant defense conferred by antioxidant enzymes and non-enzymatic antioxidants,which alleviated the peroxidation of membrane lipid,and then resulted in the decrease lipid peroxidation products in wheat under PSD.The osmotic-adjustment products were also increased by Mo application under PSD,indicating that Mo improved the osmotic adjustment ability in wheat,which is contributed to the cell turgor.2)Mo mainly affected the genes expression that related to root growth,lipid metabolism,cell wall remodeling,flavonoid metabolism and oxidation-reduction in wheat under drought stress.The RNA-sequencing(RNA-Seq)technology was applied to study the effects of Mo on the expressions of drought-response gene in wheat under drought stress.The results showed that total 509 differential expression genes(DEGs)were measured by RNA-Seq(?Log2FC??1.5,P-value<0.05)in wheat leaf between-Mo and +Mo treatments under PSD condition.Of them,282 DEGs were down-regulated by Mo application,and 227 DEGs were up-regulated by Mo application.Moreover,the results of q PCR verification are basically consistent with the results of RNA-Seq.Kyoto encyclopedia of genes and genomes(KEGG)enrichment analysis of DEGs showed that the DEGs were mainly enriched in lipid metabolism,flavonoid metabolism,nitrogen metabolism,carbon metabolism,plant hormone signal transduction and photosynthesis and so on.We focused on the potential roles of root growth,lipid metabolism,oxidation-reduction,cell wall remodeling and flavonoids metabolism in Mo-improved drought tolerance in wheat under PSD condition.3)It is highlighted the role of Mo-enzymes AO and NR in Mo-improved oxidative tolerance in wheat under drought stress.The complementary experiments showed that Mo increased AO and NR activities,correspondingly,increased ABA and NO contents,however,AO and NR inhibitors respectively decreased AO and NR activities,meanwhile,reduced ABA and NO accumulations,suggesting that Mo-enzymes AO and NR involves in regulation of Mo-induced ABA and NO synthesis in wheat under PSD,respectively.Mo enhanced activities and expressions of antioxidant enzyme,and thus alleviated oxidative damages,while these effects of Mo were reversed by AO and NR inhibitors,ABA synthesis inhibitor and NO scavenger due to decreased ABA and NO contents,but regained by exogenous ABA and NO donor,indicating that Mo induces oxidative tolerance through ABA and NO whose synthesis was activated by Mo-enzyme AO and NR in wheat under PSD,respectively.Further experiment indicated that NO scavenger inhibits activities of antioxidant enzyme induced by Mo and exogenous ABA,but the inhibitions were eliminated by NO donor.These results suggested that there are crosstalk at some degree between ABA signal pathway and NO signal pathway regulated by Mo in Mo-induced oxidative tolerance in wheat under PSD.4)The expressions of drought-resistant gene(DRG)were regulated by Mo via ABA signal pathway.In ABA-dependent pathway,Mo regulated the expressions of DRGs,such as Wrab17,mainly through the activation of upstream transcription factor(TF)gene Wabi5 under PSD,and then improved dought tolerance in wheat.In ABA-independent pathway,Mo might regulate the expressions of DRGs,such as Ta Sn RK2.3,mainly through the activation of upstream TF gene Ta AIDFa under PSD,and then improved dought tolerance in wheat.There are differences between cultivar 97003 and cultivar 97014 in Mo-improved drought tolerance by the regulation of expressions of DRGs: cultivar 97003 is by ABA-dependent pathway and ABA-independent pathway,however,cultivar 97014 is by ABA-dependent pathway.5)Mo regulated root growth by NO signal,which further affected root water uptake and homeostasis of mineral nutrients in wheat under PSD.The results showed that Mo supply and NO donors enhanced the parameters of root morphology such as lateral root length and rot tips;however,NO scavengers decreased parameters of root morphology,suggesting that the improvement of root growth by Mo is regulated through NO signal in wheat under PSD.Moreover,the root tips and lateral root length have positive correlations with rates of water uptake;meanwhile Mo supply improved the expressions of aquaporins(AQPs)in wheat root,particularly the expressions of Ta PIPs,suggesting that Mo-improved extensive root morphology and expression of AQPs were involved in Mo-increased water uptake in wheat root under PSD condition.Further study showed that Mo application decreased transpiration of wheat leaf,but increased osmotic-adjustment products potassium,calcium and magnesium contents in root,and thus increased root osmotic pressure,indicating that,on one hand,root osmotic pressure,not the transpiration,is the power of Mo-increased water uptake in wheat root under PSD condition;On the other hand,Mo supply increased mineral nutrients uptake at different degrees in wheat root,and then maintenance of the homeostasis of mineral nutrients.6)Mo regulated the membrane stability and fluidity by increased lipid contents and unsaturated fatty acid contents,which were involved in Mo-improved drought tolerance in wheat.The results showed that Mo increased the contents of DGDG,MGDG,PC and PE in wheat leaf and root by Mo-regulated the expressions of Ta MGDs,Ta DGD and Ta AAPTs that related to lipid synthesis under PSD condition.Moreover,Mo had bigger effects on contents of component of lipid in wheat root than those in wheat leaf.The ratios of digalactosyl-diacylglycerol(DGDG)to monogalactosyl-diacylglycerol(MGDG)and phosphatidylcholine(PC)to phosphatidylethanolamine(PE)in wheat were affected by Mo,which were involved in maintenance of the membranes stability of wheat under PSD condition.Mo supply enhanced the degrees of unsaturation of fatty acids by Mo-increased the expressions of fatty acids desaturase genes,which may be contributed to the cell membrane fluidity of wheat under PSD.