| Plants utilize distinct defense mechanisms against infection by various pathogens.Defenses are activated along with repressed plant growth.This antagonism is subject to a number of phytohormone or non-hormone signaling pathways,which function to balance plant growth and defense responses to ensure plant survival and a rapid switch to the normal development process under pathogen attack.Alternatively,the balancing mechanism relies on timely inactivation of defense signal transduction to reduce the repression of plant growth in the absence of a pathogen attack.Under pathogen attack,plant defense responses are induced and auxin-signaling pathway is repressed by recruiting various antagonistic signaling components.Recent studies showed that auxin-repressed protein ARP1 was critical for plant growth and defense crosstalk.This study was attempted to elucidate major components in ARP 1-regulated crosstalk.1.Function Analysis of ARP1 gene in the Growth and Disease-resistance in TobaccoIn this study,we performed screening on T-DNA insertional mutants to obtain a mutant line that caused the phenotype of growth enhancement and resistance impairment(geril).The geril mutants grew better than the WT with respect to the root length,plant height,fresh weight and leaf size.In the geril mutants,growth enhancement accompanies promoting expression of EXP1 and EXP2 genes,which encode the expansin proteins.And the expression of PR(pathogenesis-related)genes were suppressed,which is consistent with severe disease symptons when infection by viral,bacterial and oomycete in geril.Genetic analysis of geril allele identified a T-DNA tag in the ORF(open reading frame)of ARP1 gene.And the consistent results were obtained from ARP1i and P35S:ARP1 plants compared to geril mutants.These results indicate that ARP1 functions in crosstalk between plant growth and disease resistance.2.Molecular Mechanism of the ARP1 gene in Crosstalk Between Growth and Disease Resistance in TobaccoTo study the molecular mechanism of the ARP1 gene in crosstalk between tobacco growth and disease resistance,we investigated the growth and disease resistance of ARP1i,P35S:ARP1 and WT plants after treatment with typical PAMPs(pathogen-associated molecular patterns),flg22 and chitin.Analyses indicate that the growth repression by PAMPs is compromised in the ARP1i plant,and upregulated expression of ARF8(auxin response factor 8)gene was observed in the ARP1i plant.In order to study the roles of ARP1 gene in regulation of PTI pathway,we analysis H2O2 production,callose deposition,MAPK(mitogen-activated protein kinase)and NPR1(non-expression of pathogen related gene 1)genes expression in ARP1i,P35S:ARP1 and WT plants.The production of H2O2 in ARP1i was repressed,as well as callose deposition.Meanwhile,expression of MPK3,MPK11 and NPR1 were inhibited in absent of ARP1 gene.The consistent results were obtained from P35S:ARP1 plants.Our study indicates that ARP1 plays an essential role in co-regulation of the plant growth and disease resistance. |
