Study On The Effects And Relationship Of Jasmonic Acid,Phospholipase D? And G Protein In Arabidopsis Under Drought Stress

Drought stress has a very important influence on plant growth and development,metabolism,signal transmission and antioxidant enzymes.It causes a large accumulation of endogenous hormones such as Jasmonic acid(JA)in plant cells,thereby improving the adaptability and tolerance of plants to drought stress.The relationship between JA and various signal molecules is complicated.Understanding the relationship between various signal molecules will help us to better understand the mechanism of biological response to drought stress,and also provide the theoretical basis for enhancing drought resistance of crops and improving agriculture production.JA interact with a variety of signaling molecules and induce a variety of cell developmental responses.Lipoxygenase(LOX)is the first key enzyme in JA biosynthesis,which is divided into 9-LOX and 13-LOX.13-LOX is widely considered to be involved in JA biosynthesis,but whether 9-LOX is involved in this process is still unclear.Phospholipase D(PLD)is a generic term for a class of enzymes that catalyze the hydrolysis of phosphodiester bonds and base exchange reactions in phospholipid molecules.Phosphatidic acid(PA),the hydrolysis product of PLD,is considered as the second messenger in plant cells.So PLD is also considered as an important signal enzyme.PLD is encoded by 12 genes in Arabidopsis.These 12 genes play different roles in regulating plant growth and signal transmission because of their difference structure.Some studies showed that PLD?was activated quickly by salt and dehydrat.Others reported that PLD?1 and PA were involved in the JA biosynthesis.However,whether PLD?participates in the JA synthesis under drought stress has not been reported.G protein is involved in a variety of biotic and abiotic stress signaling pathways.The G?subunit is a functional subunit of the G protein and can be bind to the DRY motif on PLD?.The G?subunit regulates the expression of JA-inducible genes,and JA may act directly as a ligand in G protein signal in the Arabidopsis.However,the role of G protein in JA-regulated signals under drought stress is also unclear.To sum up,we used Arabidopsis Columbia wild type(WT),GPA1 deletion mutant(gpa1-4),phospholipase D?(PLD?)deletion mutant(pld?),and lipoxygenase(9-LOX)deletion mutants(lox1 and lox5)seeds and seedlings as experimental materials,and combined with 0.3 mol·L~-11 mannitol simulation and traditional soil water deficit method for drought stress treatment.The effects of PLD?and 9-LOX on JA biosynthesis under drought stress,and the signal transduction relationship between JA,G proteins and PLD?were studied.Understanding the role of them participate in plant drought resistance to elucidate the mechanism of JA,G protein and PLD?the signal transduction pathway under drought stress.The results are as follows:1.Drought stress markedly increased the activities of PLD and LOX and the gene expressions of PLD?and LOX1.Under drought stress,the LOX activity and JA content in pld?seedlings were significantly lower than those in WT.Both LOX and JA significantly increased after phosphatidic acid(PA)addition and were higher than those in WT.Drought stress significantly inhibited seed germination of pld?,lox1 and lox5 mutants,with the strongest inhibitory effect on lox1;Under drought stress,the application of PA promoted the seed germination of WT,pld?and lox1,but had no significant effect on lox5.Under drought stress,the application of JA promoted the seed germination of WT and pld?,but couldn`t promote the seed germination of lox1and lox5.Studies have shown that under drought stress,the enhancement of PLD activity was related to PLD?expression while the increasing activity of LOX was related to LOX1 and LOX5 expressions,with the dominant role from LOX1.PLD?/PA was located at the upstream of 9-LOX and involved in the JA synthesis.All PLD?,LOX1 and LOX5 participated in seed germination of Arabidopsis under drought stress,with a dominant role of LOX1 in this process.Both PLD?and 9-LOX were involved in PA and JA-mediated seed germination.2.JA regulated the PLD activity and expression of PLD?gene by regulating GPA1;GPA1 participated in the regulation of exogenous MeJA on seed germination,GPA1 and PLD?didn`t participate in the regulation of endogenous JA on seed germination;exogenous MeJA decreased the MDA content and REC level in WT,and increased the MDA content and REC level in both gpa1-4 and pld?mutants.JA synthesis inhibitor had no significant effect on MDA content and REC level;The stomatal density and opening of WT,gpa1-4 and pld?were increased significantly under droeght stress.Applicating of MeJA reduced significantly the stomatal density of WT,gpa1-4 and pld?,had no significant effect on the stomatal opening of WT and gpa1-4,but reduced significantly of the stomatal opening of pld?;Under drought stress,the gene expression of drought response gene RD29A was higher than that of pld?significantly in WT,after applicating of MeJA,the expression of RD29A was significantly up-regulated in WT and pld?.Studies had shown that under drought stress,JA regulatesPLD activityandPLD?geneexpressionwas a concentration-dependent manner,and G protein was also involved in this regulation process;GPA1 and PLD?are involved in the regulation of JA on seed germination.GPA1 and PLD?played a role in the protection of MeJA on cell membrane;The loss of PLD?gene maked drought resistance weaken in Arabidopsis;MeJA can improve drought tolerance by decreasing stomatal density and reducing stomatal opening in plants,and speculating that the regulation of this process dependented on G protein;One of the reasons why pld?mutant plants lowed drought-tolerant was that the expression of RD29A in response to drought stress was lowed,and applicating of MeJA can up-regulate the expression of RD29A gene to increase the drought tolerance of plants.