Molecular Mechnism Of Jasmonate Mediated Low-Boron-Induced Growth Inhibition In Arabidopsis

Boron(B)is an essential micronutrient for plant growth and development,and it widely affects on the series processes of physiological and biochemical in plant.Jasmonic acid(JA)is a new type of plant growth regulator,which widely exists in all higher plants.JA regulates the plant growth and development,as well as responses to various biotic and abiotic stresses.In our previous studies,response to B deficiency both in the proteome of Brassica napus and in the transcriptome of Arabidopsis,JA was found to be involved in B deficiency in Brassica napus and Arabidopsis.Therefore,to better understand the physiological and molecular mechanism that JA modulates the low B response in Arabidopsis,this study studied the molecular mechanisms on JA involving in low B response in Arabidopsis under long-and short-term low B stressed.The main results are obtained as follows: 1 Low B induces JA levels,which negatively regulate the plant growthLow B significantly inhibited the primary root growth by reducing the length and the cell numbers in meristem zone and elongation zone,and restraining the average length of cells in elongation zone.Low B induces JA levels,the JA concentrations in the 0.1-?M B treated shoots and roots were ?7.9-fold and ?2.8-fold compared to those in the 30-?M B treated plants,respectively.Exogenous JA or low B significantly inhibited the growth of shoot and root,while exogenous JA synthesis inhibitor(DIECA)could partially restore the primary root growth under low B stress by restoring the length of non-root-hair zone(NRHZ)and the division activity in root tip.We found that 517 genes were overlaid between the responsive genes in the B deficiency transcriptome data and the responsive genes treated with methl-jasmonate(Me JA).Of which,470 genes(?90%)were show the same expression pattern as up-regulation or down-regulation by B deficiency or Me JA.These results indicate that low B induces the JA synthesis and JA plays an important role in the molecular level in plant growth inhibition by B deficiency.2 ERF012/018 binds to the promoter of JA biosynthetic genes and upregulates the expression of JA biosynthetic genesBioinformatics analysis showed that ERF018 could bind to the cis elements O-box on the promoter of JA synthesis genes AOC1 and AOC3.ERF012 and ERF018 belonging to the same ERFs subfamily were earlier low B responsive genes,which are induced at 3 h by B deficiency.The yeast one hybrid(Y1H)and tobacco transient expression showed that ERF012 and ERF018 could bind to the promoter of JA biosynthetic genes and upregulate the expression of JA biosynthesis genes.Transgenic lines of ERF012 overexpression confirmed that ERF012 activated the expression of JA biosynthesis gene and significantly increased JA level,but ERF012 negatively regulated plant growth.Similarly,ERF018 overexpression lines could up-regulate the expression of JA synthesis gene,ERF018 also negatively regulated plant growth.These results reveal that ERF012/018 could bind to the promoter of JA biosynthetic genes and upregulated the expression of JA biosynthesis genes.3 Low B triggers JA signaling to regulate the plant growthThe JAR1,COI1 and MYC2 are two important components in JA signaling pathway.The jar1-1,coi1-2 and myc2 mutants showed low-B unsensitivity,which mainly reflected that the primary root length and shoot fresh weight of the jar1-1,coi1-2 and myc2 mutants were significantly better than those in Col-0.Low B induced the level of JA-Ile,a bioactive form in JA signaling pathway.The fluorescence intensity of JAZ3:GFP decreased along with the time of low-B treatment,indicating that the JA signaling was enhanced under low B stress.Simultaneously,exogenous JA-Ile could inhibit the growth of jar1-1 mutant under B deficiency.These results show that low B triggeres the JA signaling pathway,which negatively regulates the plant growth under low B condition in Arabidopsis.4 JA acts synergistically ethylene signaling to mediate the primary root growth under low B conditionThe expressions of ethylene biosynthesis gene were up-regulated in B deficiency.Exogenous application of ethylene biosynthesis inhibitor(AVG)could partially alleviate the inhibition of primary root growth by B deficiency.Ethylene-overproduction mutant eto1 and ethylene-insensitive mutant etr1 showed sensitivity and insensitivity to B deficiency,respectively,suggesting that ethylene is involved in inhibition of primary root growth under B deficiency.Indeed,the expression of ethylene responsive marker genes were significantly lower in jar1-1 mutants than those in Col-0 under low B condition,and ethylene response in jar1-1 was weaker under B deficiency.Interestingly,exogenous ACC or endogenous ACC/ET could inhibit the growth of jar1-1 under B deficiency.These suggested that JA signal and ethylene signal synergistically regulated the primary root growth under B deficiency.Therefore,the decrease of ethylene response in jar1-1 was not related to the expression of ethylene biosynthesis genes and signal pathway genes.It was found that the protein level of transcription factor EIN3 is inhibited in jar1-1 under B deficiency.These results indicate that JA can interact with the protein level of EIN3,and coordinate with ethylene to regulate the inhibition of boron deficiency on primary root growth.5 JA indirectly affects the uptake and transport of boronExogenous JAs did not change the expressions of B uptake and transport genes in Arabidopsis.The biomass and boron concerntration of jar1-1 mutant were significantly higher than that of Col-0 under B deficiency.But there was no significant difference in the expression of B uptake and transport related genes between jar1-1 mutant and Col-0.In addition,the primary root length of nip5;1 jar1-1 was significantly longer than that of nip5;1 mutant under B deficiency,but it was significantly shorter than that of Col-0 and jar1-1.It is suggested that JA did not directly regulate the B uptake,but regulated the B uptake was by affecting the root system under B deficiency.Under B deficiency,the expressions of JA biosynthesis and signaling gene were increased in nip5;1 and bor1-1 mutants,and the expression of JA signaling response gene was enhanced,which indicated that JA was involved in low B response in nip5;1 and bor1-1 mutants.In conclusion,our study reveals that we identified the ethylene response factor ERF012/018 as the boron responsive genes.ERF012/018 binds to the promoters of JA biosythesis genes(AOC1 and AOC3),and up-regulates the expression of JA biosythesis gene.The increased JA triggers JA signaling via JA-Ile catalyzed by JAR1 under B deficiency,then the activated JA signaling pathway inhibits the primary root growth.Meanwhile,JA synergistically interact with ethylene through the ethylene signal transcription factor EIN3/EIL1 to inhibit the primary root growth,thus affecting the B uptake.