TGA family is an important group of bZIP transcription factors in plant,which regulates the downstream target genes by binding to the as-1 cis-elements in the promoter region and subsequently activating or inhibiting their expression,finally regulating the resistance or development of floral organ.The first TGA gene was identified in tobacco.Subsequently,TGA members were widely characterized in arabidopsis,rice and apple.In arabidopsis,they constitute a multigene family comprising 10 members based on genome sequence analyses.The members of TGA family can be divided into five subgroups (Ⅰ:TGA1 and TGA4;Ⅱ:TGA2,TGA5 and TGA6;Ⅲ:TGA3 and TGA7;Ⅳ:TGA9 and TGA10;Ⅴ:PAN) according to their sequence similarity.The members of Ⅰ,Ⅱ and Ⅲ subgroups are mainly involved in disease resistance.Yeast two-hybrid and pull-down results showed that all members of subgroup Ⅰ,Ⅱ,and Ⅲ could interact with NPR1 protein which is the key positive regulator in SA signaling pathway.EMSA results indicated that the interaction between TGA and NPR1 could enhance the expression of pathogenesis-related (PR) genes and disease resistance.However,their roles were different in basal and systemic acquired resistance (SAR):tga3 mutants showed a defect in basal resistance,whereas the induced resistance was unaffected.TGA1 and TGA4 were involved in regulation of basal resistance and SAR.The tga2/5/6 triple mutants but not tga6 or tga2/5 double mutants were defective in SAR,a phenotype similar to that of the nprl mutants,indicating functional redundancy among TGA2,TGA5 and TGA6.Yeast two-hybrid screen revealed that TGA transcription factors of subgroup Ⅱ could interact with glutaredoxin GRX480 to mediate the repression of the marker genes of JA signaling by SA,and they also could interact with GRAS protein SCL14 to increase the expression of CYP81D11 and GSTU7 in an NPR1-independent manner and enhance the tolerance to xenobioties.In addition,the primary and lateral root growth was affected in tga1/4 and nrt2.1/2.2 mutants.ChIP and yeast one-hybrid assay results showed that TGA 1 and TGA4 regulated the nitrate response via binding to the promoters of NRT2.1 and NRT2.2 to regulate their expression.TGA3 was also involved in the long-distance transport of cadmium.The members of subgroup Ⅳ and Ⅴ played an importance role in the regulation of floral organ development.tga9/10 mutants have defects in male gametogenesis that were similar to those in roxy1/2 mutants.PAN could interact with NPR1-like proteins BOP1 and BOP2.Both pan and bop1/2 double mutants revealed a pentamerous arrangement of sepals,which suggested that a similar signaling mechanism might be used between floral organ development and disease resistance.Finally,the research directions of TGA transcription factors was discussed,which will provide a reference for researchers in this field.
TGA transcription factorsnonexpressor of pathogenesis-related genes 1resistancedevelopment
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