The C-terminal half of Phytophthora infestans RXLR effector AVR3a is sufficient to trigger R3a-mediated hypersensitivity and suppress INF1-induced cell death in Nicotiana benthamiana
The C-terminal half of Phytophthora infestans RXLR effector AVR3a is sufficient to trigger R3a-mediated hypersensitivity and suppress INF1-induced cell death in Nicotiana benthamiana
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DOI：
10.1111/j.1365-313x.2006.02866.x
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发表时间：
2006-10-01
期刊：
影响因子：
7.2
通讯作者：
Kamoun, Sophien
中科院分区：
文献类型：
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作者：
Bos, Jorunn I. B.;Kanneganti, Thirumala-Devi;Kamoun, Sophien
疫霉RXLR细胞质效应物AVR3a对携带R3a基因的马铃薯植株具有无毒作用。Avr3a的两个等位基因编码的分泌蛋白只有三个氨基酸残基不同，其中两个在成熟蛋白中。无毒株携带Avr3a等位基因，编码Avr3a (KI)（含氨基酸C-19、K-80和I-103），而有毒株只表达Avr3a毒力等位基因，编码Avr3a (EM) （S-19、E-80和M-103）。只有AVR3a（KI）蛋白在植物细胞质内被识别，并触发r3a介导的超敏反应。与其他卵菌无毒蛋白类似，AVR3a（KI）携带一个信号肽，其后是一个以共识RXLR序列为中心的保守基序，其功能类似于疟疾寄生虫的宿主细胞靶向信号。Avr3a和R3a的相互作用可以通过它们在烟叶中的瞬时共表达来重建。我们利用N. benthamiana实验系统进一步表征Avr3a-R3a相互作用。AVR3a（KI）激活R3a依赖于泛素连接酶相关蛋白SGT1和热休克蛋白HSP90。AVR3a（KI）和AVR3a（EM）蛋白在植物中同样稳定，这表明r3a介导的死亡差异不能归因于AVR3a（EM）蛋白的不稳定性。AVR3a（KI）能够抑制P. infestans的卵磷脂INF1诱导的细胞死亡，提示该蛋白可能具有毒力功能。结构-功能实验表明，AVR3a（KI）的75个氨基酸的c端部分（不包括RXLR区域）足以发挥无毒和抑制功能，这与AVR3a（KI）和其他RXLR效应物的n端区域参与分泌和靶向作用，但不是效应物活性所必需的观点一致。我们还发现成熟AVR3a的多态氨基酸K-80和I-103都参与了效应功能。
The RXLR cytoplasmic effector AVR3a of Phytophthora infestans confers avirulence on potato plants carrying the R3a gene. Two alleles of Avr3a encode secreted proteins that differ in only three amino acid residues, two of which are in the mature protein. Avirulent isolates carry the Avr3a allele, which encodes AVR3a(KI) (containing amino acids C-19, K-80 and I-103), whereas virulent isolates express only the virulence allele avr3a, encoding AVR3a(EM) (S-19, E-80 and M-103). Only the AVR3a(KI) protein is recognized inside the plant cytoplasm where it triggers R3a-mediated hypersensitivity. Similar to other oomycete avirulence proteins, AVR3a(KI) carries a signal peptide followed by a conserved motif centered on the consensus RXLR sequence that is functionally similar to a host cell-targeting signal of malaria parasites. The interaction between Avr3a and R3a can be reconstructed by their transient co-expression in Nicotiana benthamiana. We exploited the N. benthamiana experimental system to further characterize the Avr3a-R3a interaction. R3a activation by AVR3a(KI) is dependent on the ubiquitin ligase-associated protein SGT1 and heat-shock protein HSP90. The AVR3a(KI) and AVR3a(EM) proteins are equally stable in planta, suggesting that the difference in R3a-mediated death cannot be attributed to AVR3a(EM) protein instability. AVR3a(KI) is able to suppress cell death induced by the elicitin INF1 of P. infestans, suggesting a possible virulence function for this protein. Structure-function experiments indicated that the 75-amino acid C-terminal half of AVR3a(KI), which excludes the RXLR region, is sufficient for avirulence and suppression functions, consistent with the view that the N-terminal region of AVR3a(KI) and other RXLR effectors is involved in secretion and targeting but is not required for effector activity. We also found that both polymorphic amino acids, K-80 and I-103, of mature AVR3a contribute to the effector functions.