Barker Claire L, Baillie Brett K, Hammond-Kosack Kim E, Jones Jonathan D G, Jones David A
Plant Cell Biology Group, Research School of Biological Sciences, The Australian National University, Canberra ACT 0200, Australia.
Plant J. 2006 May;46(3):385-99. doi: 10.1111/j.1365-313X.2006.02699.x.
The tomato Cf-9 gene confers resistance to races of the leaf mould fungus Cladosporium fulvum that carry the Avr9 avirulence gene. Cf-9 was isolated by transposon tagging using a modified maize Dissociation (Ds) element. This generated an allelic series of Ds-induced mutations of Cf-9, of which two were found to confer novel phenotypes in a screen for mutants affecting wild-type Cf-9 function in trans. Genetic and molecular analysis of these mutants suggested semidominant, Avr9-dependent, negative-interfering mutations involving Ds insertions in a defined subregion of Cf-9. Interference was associated with expression of the 5'-end of Cf-9 upstream of the Ds insertions in these mutants, suggesting that truncated Cf-9 proteins were the likely cause of interference. Transgenic tomato lines harbouring Cf-9 constructs with premature stop codons in positions similar to the Ds insertions also showed interference, indicating that the presence of Ds was not required for interference to occur. Interestingly, interference in these transgenic lines was completely dominant and was associated with a pronounced developmental phenotype that was dependent on co-expression of Cf-9, Avr9 and a truncated Cf-9 transgene. However, interference with a weakly autoactive Hcr9 gene was Avr9-independent and did not cause a developmental phenotype, suggesting that localized restoration of Cf-9/Avr9-dependent cell death was responsible for the developmental phenotype. The restricted region in which truncation of Cf-9 results in dominant-negative interference suggests that leucine-rich repeats (LRR) 16-19 of Cf-9 may mediate dimerization of Cf-9 and LRRs 20-23 may mediate interactions with downstream partner proteins required for Cf-9 signalling, or vice versa.
番茄Cf-9基因赋予对携带Avr9无毒基因的叶霉病菌株的抗性。Cf-9是通过使用改良的玉米解离（Ds）元件进行转座子标签法分离得到的。这产生了一系列由Ds诱导的Cf-9等位基因突变，其中两个在筛选影响野生型Cf-9功能的反式突变体时被发现具有新的表型。对这些突变体的遗传和分子分析表明，它们是涉及Ds插入Cf-9特定亚区域的半显性、Avr9依赖性、负干扰突变。干扰与这些突变体中Ds插入位点上游Cf-9 5'端的表达有关，表明截短的Cf-9蛋白可能是干扰的原因。在与Ds插入位点相似位置带有提前终止密码子的Cf-9构建体的转基因番茄品系也表现出干扰，这表明干扰的发生不需要Ds的存在。有趣的是，这些转基因品系中的干扰是完全显性的，并且与一种明显的发育表型相关，该表型依赖于Cf-9、Avr9和截短的Cf-9转基因的共表达。然而，对弱自激活的Hcr9基因的干扰是Avr9非依赖性的，并且不会导致发育表型，这表明Cf-9/Avr9依赖性细胞死亡的局部恢复是发育表型的原因。Cf-9截短导致显性负干扰的受限区域表明，Cf-9的富含亮氨酸重复序列（LRR）16 - 19可能介导Cf-9的二聚化，而LRR 20 - 23可能介导与Cf-9信号传导所需的下游伴侣蛋白的相互作用，反之亦然。
