Mesarich Carl H, Griffiths Scott A, van der Burgt Ate, Okmen Bilal, Beenen Henriek G, Etalo Desalegn W, Joosten Matthieu H A J, de Wit Pierre J G M
Mol Plant Microbe Interact. 2014 Aug;27(8):846-57. doi: 10.1094/MPMI-02-14-0050-R.
The Cf-5 gene of tomato confers resistance to strains of the fungal pathogen Cladosporium fulvum carrying the avirulence gene Avr5. Although Cf-5 has been cloned, Avr5 has remained elusive. We report the cloning of Avr5 using a combined bioinformatic and transcriptome sequencing approach. RNA-Seq was performed on the sequenced race 0 strain (0WU; carrying Avr5), as well as a race 5 strain (IPO 1979; lacking a functional Avr5 gene) during infection of susceptible tomato. Forty-four in planta-induced C. fulvum candidate effector (CfCE) genes of 0WU were identified that putatively encode a secreted, small cysteine-rich protein. An expressed transcript sequence comparison between strains revealed two polymorphic CfCE genes in IPO 1979. One of these conferred avirulence to IPO 1979 on Cf-5 tomato following complementation with the corresponding 0WU allele, confirming identification of Avr5. Complementation also led to increased fungal biomass during infection of susceptible tomato, signifying a role for Avr5 in virulence. Seven of eight race 5 strains investigated escape Cf-5-mediated resistance through deletion of the Avr5 gene. Avr5 is heavily flanked by repetitive elements, suggesting that repeat instability, in combination with Cf-5-mediated selection pressure, has led to the emergence of race 5 strains deleted for the Avr5 gene.
番茄的Cf-5基因赋予对携带无毒基因Avr5的真菌病原体番茄叶霉病菌株的抗性。尽管Cf-5已被克隆，但Avr5仍然难以捉摸。我们报告了使用生物信息学和转录组测序相结合的方法克隆Avr5。在易感番茄感染期间，对已测序的0号生理小种菌株（0WU；携带Avr5）以及5号生理小种菌株（IPO 1979；缺乏功能性Avr5基因）进行了RNA测序。鉴定出0WU的44个在植物中诱导的番茄叶霉病菌候选效应子（CfCE）基因，这些基因推测编码一种分泌的、富含半胱氨酸的小蛋白。菌株间的表达转录本序列比较揭示了IPO 1979中有两个多态性CfCE基因。其中一个在与相应的0WU等位基因互补后，赋予IPO 1979对Cf-5番茄的无毒力，证实了Avr5的鉴定。互补还导致易感番茄感染期间真菌生物量增加，表明Avr5在毒力中起作用。所研究的8个5号生理小种菌株中有7个通过缺失Avr5基因逃避了Cf-5介导的抗性。Avr5两侧有大量重复元件，这表明重复序列的不稳定性与Cf-5介导的选择压力相结合，导致了缺失Avr5基因的5号生理小种菌株的出现。
