Dissecting The Molecular Mechanism Of An Arabidopsis MYB Transcription Factor That Regulates Jasmonate Synthesis And Insect Resistance

Jasmonic acid(JA)is a lipogenic phytohormone in higher plants,which plays an important role in plant growth and development,biotic stress,abiotic stress and other processes.In a previous work,it was found that the expression of a R2R3-type AtMYBx was specifically induced by JA and overexpression of AtMYBx could promote JA synthesis by regulating JA synthesis-related genes.In addition,overexpression of AtMYBx can promote the premature senescence of plants under natural and dark induction conditions.However,it is not clear how AtMYBx regulates the synthesis of JA and whether it is involved in the regulation of insect and disease resistance.Therefore,the function and regulatory mechanism of AtMYBx were further investigated in this study.The results and conclusions are as follows:1.Through utilizing green fluorescent protein(GFP),subcellular localization assay of AtMYBx-GFP in tobacco leaf showed AtMYBx-GFP was located both in the nucleus and at the plasma membrane.It was predicted that AtMYBx contains multiple putative myristoylation and palmitoylation sites.After these sites in AtMYBx were mutated to be Ala or Ser,they did not significantly change the subcellular localization.Histochemical staining of Pro AtMBx-GUS transgenic lines at different development stages showed that Pro AtMYBx was expressed in leaves,hypocotyls,root caps,lateral root primordia,stigma tips and sepals.In addition,after injury treatment,GUS staining was significantly stronger at the injured sites of leaves of Pro AtMBx-GUS transgenic lines.2.Under exogenous JA treatment,the elongation of the primary root of AtMYBx overexpression lines was inhibited,while the mutant lines and dominant suppression lines of AtMYBx showed an opposite change.In addition to response to JA treatment,AtMYBx also showed different responses to biotic stress.Sclerotinia sclerotiorum inoculation test showed that AtMYBx overexpression lines were susceptible to S.sclerotiorum challenge and did not participate in disease resistance.Furthermore,Spodoptera exigua feeding test showed that AtMYBx overexpression lines were more resistant to larval biting than control lines.3.The putative downstream target genes of AtMYBx were identified by q RT-PCR and Dual-LUC tests.The results showed that AtMYBx could activate the expression of multiple genes coding for enzymes involed in JA and glucosinolate biosynthesis,which include AOS(allene oxide synthase),LOX2(lipoxyigenase 2),OPR2(OPDA reductase 2),CYP79B3(Cytochrome P450 79B3),VSP1(Vegetative storage protein 1)and other genes.Multiple cis-acting elements of AtMYBx were identified through Dual LUC and electrophoretic mobility shift assay(EMSA).Besides,EMSA verified the binding of AtMYBx to potential fragments in the promoters of LOX2 and LOX4 in vitro.To summarize,this study found that an AtMYBx gene that is induced by JA and wounding treatments.AtMYBx regulate growth and development as well as insect resistance through modulating the transcription of genes involved in JA biosynthesis.These results lay a theoretical foundation for the cultivation of insect-resistant crops and the improvement of plant yield.