Background

The rice (Oryza sativa) gene Xa7 has been hypothesized to be a typical executor resistance gene against Xanthomonas oryzae pv. oryzae (Xoo), and has conferred durable resistance in the field for decades. Its identity and the molecular mechanisms underlying this resistance remain elusive.

Results

Here, we filled in gaps of genome in Xa7 mapping locus via BAC library construction, revealing the presence of a 100-kb non-collinear sequence in the line IRBB7 compared with Nipponbare reference genomes. Complementary transformation with sequentially overlapping subclones of the BACs demonstrated that Xa7 is an orphan gene, encoding a small novel protein distinct from any other resistance proteins reported. A 27-bp effector binding element (EBE) in the Xa7 promoter is essential for AvrXa7-inducing expression model. XA7 is anchored in the endoplasmic reticulum membrane and triggers programmed cell death in rice and tobacco (Nicotiana benthamiana). The Xa7 gene is absent in most cultivars, landraces, and wild rice accessions, but highly homologs of XA7 were identified in Leersia perrieri, the nearest outgroup of the genus Oryza.

Conclusions

Xa7 acts as a trap to perceive AvrXa7 via EBE_AvrXa7 in its promoter, leading to the initiation of resistant reaction. Since EBE_AvrXa7 is ubiquitous in promoter of rice susceptible gene SWEET14, the elevated expression of which is conducive to the proliferation of Xoo, that lends a great benefit for the Xoo strains retaining AvrXa7. As a result, varieties harboring Xa7 would show more durable resistance in the field. Xa7 alleles analysis suggests that the discovery of new resistance genes could be extended beyond wild rice, to include wild grasses such as Leersia species.

中文翻译：

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Xa7 是一个含有 AvrXa7 启动子陷阱的小孤儿基因，可导致对米黄单胞菌 Pv. 的持久抗性。米霉

背景

水稻 ( Oryza sativa ) 基因Xa7被假设为针对米黄单胞菌 ( Xanthomonas oryzae pv) 的典型执行抗性基因。oryzae ( Xoo )，数十年来在该领域赋予了持久的抗性。其身份和这种耐药性背后的分子机制仍然难以捉摸。

结果

在这里，我们通过 BAC 文库构建填补了Xa7定位位点中基因组的空白，揭示了与日本晴参考基因组相比，IRBB7 品系中存在 100 kb 非共线序列。BAC 的顺序重叠亚克隆的互补转化证明Xa7是一个孤儿基因，编码一种与报道的任何其他抗性蛋白不同的小新蛋白。Xa7启动子中的 27 bp 效应结合元件 (EBE)对于 AvrXa7 诱导表达模型至关重要。XA7 锚定在内质网膜上，并触发水稻和烟草（烟草）的程序性细胞死亡。大多数栽培品种、地方品种和野生稻种质中不存在Xa7基因，但在稻属最近的外群Leersia perrieri中鉴定出了 XA7 的高度同源物。

结论

Xa7作为陷阱通过其启动子中的EBE _AvrXa7感知AvrXa7 ，导致耐药反应的启动。由于EBE _AvrXa7普遍存在于水稻易感基因SWEET14的启动子中，其表达量升高有利于Xoo的增殖，这对于保留AvrXa7的Xoo品系来说是非常有利的。因此，携带Xa7的品种将在田间表现出更持久的抗性。Xa7等位基因分析表明，新抗性基因的发现可以扩展到野生稻以外，包括野草，例如莱尔西亚物种。