白桦TGA基因家族全基因组鉴定及表达特性分析

Genome-wide identification and expression analysis of TGA family genes in birch

TGA转录因子是bZIP转录因子(basic region-leucine zippers)家族成员,是植物中最早鉴定得到的一类转录因子,可以结合基因启动子的TGACG序列,调节靶基因的转录水平,在植物防御反应及花器官发育中发挥重要作用。本研究从白桦的基因组数据库中筛选出6条TGA基因,分别命名为BpTGA1~BpTGA6。生物信息分析结果表明:白桦TGA家族蛋白主要富含酸性氨基酸,亚细胞定位在细胞核,无信号肽结构,二级结构以α-螺旋为主,均属于亲水性蛋白,无跨膜结构。白桦TGA家族基因启动子区存在10~40个不等的增强启动元件(CAAT-box)和核心启动子元件(TATA-box),还具有非生物胁迫和逆境胁迫响应相关元件。系统进化分析结果表明:白桦TGA家族基因与拟南芥TGA家族基因亲缘关系较近。RT-qPCR结果表明,白桦TGA家族基因在根、茎、叶中的表达各有不同,BpTGA3在根中的表达量较高;BpTGA1、BpTGA2、BpTGA4和BpTGA6在茎中的表达量较高;BpTGA5在叶片中表达量较高。该家族成员中BpTGA2、BpTGA4、BpTGA5响应链格孢霉菌和立枯丝核菌侵染,BpTGA5对两种病原菌的响应最为强烈,在侵染24 h和48 h时表达量达到最高,分别为对照的17.45倍和328.76倍。本研究为进一步探究白桦TGA转录因子在白桦中的作用奠定了基础。

TGA transcription factor,a member of the basic region-leucine zippers(bZIP)transcription factor family,is one of the earliest identified transcription factors in plants.It can regulate the transcription level of target genes through binding to the TGACG sequence of the gene promoters,and plays an important role in plant defense responses and floral organ development.In this study,six TGA genes were identified from the genome database of Betula platyphylla,named BpTGA1-BpTGA6.Bioinformatics analysis showed that the birch TGA family proteins were mainly rich in acidic amino acids,subcellular localization in the nucleus,and no signal peptide structure;the secondary structures of birch TGA protein were mainlyα-helix,and all of the birch TGA family genes were hydrophilic proteins which have no transmembrane structure.There were 10~40 enhanced promoter elements(CAAT-box)and core promoter elements(TATA-box)in the promoter region of birch TGA family genes.Also,these regions have abiotic stress and biotic stress response-related elements,indicating that members of this family may be involved in environmental responses.The results of phylogenetic analysis indicated that the birch TGA family genes were closely related to those of Arabidopsis thaliana.The results of real-time fluorescence quantitative PCR(RT-qPCR)suggested that the expression level of birch TGA family genes in the roots,stems and leaves were different;The expression level of BpTGA3 was higher in roots,and BpTGA1,BpTGA2,BpTGA4,and BpTGA6 were higher in stems,whereas BpTGA5 was highly expressed in leaves.Among the members of TGA family genes,BpTGA2,BpTGA4,and BpTGA5 responded to the infection of Alternaria alternata and Rhizoctonia solani.Among them,BpTGA5 responded most strongly to both pathogens,and the expression reached the highest level at 24 h and 48 h after infection,which were 17.45 times and 328.76 times of the control,respectively.This study lays a foundation for further exploring the role of birch TGA transcription factor in birch.