杨树BAG基因的鉴定及表达模式分析

【目的】杨树是我国人工林的重要组成部分,也是公认的模式木本植物。植物BAG蛋白作为保守的分子伴侣,在生长发育和抗逆性中起到关键作用。研究杨树BAG蛋白家族的进化与表达模式,鉴定BAG基因的生物学功能对于林木遗传改良具有重要的指导意义。【方法】以拟南芥7个BAG蛋白为诱饵,搜索毛果杨、水稻和小立碗藓在线数据库(https://phytozome.jgi.doe.gov)获得这3个物种同源的BAG蛋白。利用生物信息学构建毛果杨、拟南芥、水稻和小立碗藓BAG蛋白的系统进化树,分析这些蛋白的生化特性及进化关系。结合杨树芯片(http://bar.utoronto.ca)数据,利用qRT-PCR检测杨树BAG基因的组织和逆境(旱和热胁迫)表达模式。【结果】毛果杨包含14个BAG基因,按照国际命名法(以染色体位置进行排序),将其命名为PtrBAG1—PtrBAG14。系统进化树表明杨树、拟南芥、水稻和小立碗藓BAG蛋白相对保守,大体可以分为2个亚家族。第1个亚家族中,大部分BAG蛋白N端含有UBL结构域,可能作为分子桥梁参与降解某些蛋白;第2个亚家族的大部分BAG蛋白含有IQ结构域,意味着这些蛋白可能与Ca²⁺信号相关。杨树BAG基因在不同逆境处理(热胁迫和干旱胁迫)条件下有不同的表达模式。热处理诱导所有BAGs基因表达发生变化,其中BAG1、BAG4、BAG6、BAG7和BAG8表达被激活,而另9个BAG基因的表达被抑制;特别是,热诱导BAG4和BAG6表达上调超过90倍。干旱胁迫条件下,大部分BAG表达变化幅度很小。组织表达模式分析表明,大部分杨树BAG基因在根、叶、芽、小苗、雌花序、雄花序和木质部中表达量很低,只有BAG2和BAG12在木质部中大量表达。【结论】杨树BAG家族共有14个成员,大体分为2个亚家族,在进化上与本文选用的陆生植物拟南芥和水稻BAG蛋白有更高的相似性。杨树14个BAG基因可能都参与了热胁迫调控,但不同成员在抗热过程中起不同作用。相比而言,大部分杨树BAG基因可能并不参与抗旱。值得指出的是,杨树BAG4和BAG6可能在热胁迫中作用最明显,而BAG2和BAG12可能参与木材形成。

Identification and Expression Pattern Analyses of Populus BAG Genes

【Objective】Poplar(Populus)is widely planted in China and usually used as a model tree.As conserved molecular chaperon,plant BAG proteins play critical roles in growth,development and stress responses.Study on the evolution and biological functions of Populus BAG genes is useful for genetic improvement of tree species.【Method】Arabidopsis BAG proteins were used as keywords to search online database(https://phytozome.jgi.doe.gov/)in order to identify the homologous BAGs from poplar(Populus trichocarpa),rice(Oryza sativa)and moss(Physcomitrella patens).Protein structures and evolutionary relationship of these BAG proteins were analyzed using the bioinformatic method.Tissue expression patterns and stress(drought and heat)responses of Populus BAG genes were detected based on the microarray(http://bar.utoronto.ca/)and qRT-PCR data.【Result】P.trichocarpa contains fourteen BAG genes,respectively named as PtrBAG1 to PtrBAG14 according to the international rules for nomenclature(ordered on their positions on the chromosome).BAG proteins are relatively conserved among poplar,Arabidopsis,rice and moss.These Populus BAG proteins are divided into two subfamilies.The members in subfamilyⅠcontains an UBL domain,suggesting that these proteins might function as bridges to assist the degradation of some proteins.The members in subfamilyⅡhave an IQ domain,implying the potential roles of these proteins in Ca^2+signaling.Poplar BAG genes exhibited different stress(drought and heat)responses.For example,heat treatment resulted in visible changes in BAG expression.Of them,BAG1,BAG4,BAG6,BAG7 and BAG8 were activated whereas others were suppressed by heat stress.By contrast,there were few alterations in the expression of most BAG genes under the treatment of drought.Particularly,heat treatment induced up regulated expression of BAG 4 and BAG 6 by 90 folds.Tissue expression analysis indicated that most of BAGs had little expression in detected tissues(root,leaves,shoot,seedling,female catkins,male catkins and xylem).However,BAG 2 and BAG 12 were highly expressed in xylem.【Conclusion】Poplar BAG family contains 14 members,which are basically divided into two subfamilies.These BAG proteins are closer to BAG homologs from Arabidopsis and rice than those from moss.All poplar BAG genes are responsive to heat stress but not to drought stress.In particular,BAG 4 and BAG 6 are most highly induced by heat treatment.BAG 2 and BAG 12 are likely involved in wood formation.