Table_9_The NLR Protein Encoded by the Resistance Gene Ty-2 Is Triggered by the Replication-Associated Protein Rep/C1 of Tomato Yellow Leaf Curl Virus.xlsx

The whitefly-transmitted tomato yellow leaf curl virus (TYLCV) is one of the most destructive viral pathogens of cultivated tomato. To combat TYLCV, resistance gene Ty-2 has been introduced into cultivated tomato (Solanum lycopersicum) from wild tomato species Solanum habrochaites by interspecific crossing. Introgression lines with Ty-2 contain a large inversion compared with S. lycopersicum, which causes severe suppression of recombination and has hampered the cloning of Ty-2 so far. Here, we report the fine-mapping and cloning of Ty-2 using crosses between a Ty-2 introgression line and several susceptible S. habrochaites accessions. Ty-2 was shown to encode a nucleotide-binding leucine-rich repeat (NLR) protein. For breeding purposes, a highly specific DNA marker tightly linked to the Ty-2 gene was developed permitting marker-assisted selection. The resistance mediated by Ty-2 was effective against the Israel strain of TYLCV (TYLCV-IL) and tomato yellow leaf curl virus-[China : Shanghai2] (TYLCV-[CN : SH2]), but not against tomato yellow leaf curl Sardinia virus (TYLCSV) and leafhopper-transmitted beet curly top virus (BCTV). By co-infiltration experiments we showed that transient expression of the Rep/C1 protein of TYLCV, but not of TYLCSV triggered a hypersensitive response (HR) in Nicotiana benthamiana plants co-expressing the Ty-2 gene. Our results indicate that the Rep/C1 gene of TYLCV-IL presents the avirulence determinant of Ty-2-mediated resistance.

番茄黄化叶卷病毒（TYLCV），一种由白粉虱传播的极具破坏性的病毒性病原体，是栽培番茄中最为严重的病毒病原之一。为应对TYLCV，通过种间杂交，将野生番茄物种Solanum habrochaites中的抗性基因Ty-2引入栽培番茄（Solanum lycopersicum）。与S. lycopersicum相比，含有Ty-2的导入系具有较大的倒位，这严重抑制了重组，迄今为止阻碍了Ty-2的克隆。本研究通过将Ty-2导入系与多个易感S. habrochaites资源进行杂交，报告了Ty-2的精细定位和克隆。研究表明，Ty-2编码一种核苷酸结合的富含亮氨酸重复（NLR）蛋白。为育种目的，开发了一种高度特异的DNA标记，该标记与Ty-2基因紧密连锁，允许进行标记辅助选择。由Ty-2介导的抗性对以色列株系TYLCV（TYLCV-IL）和番茄黄化叶卷病毒-[中国：上海2]（TYLCV-[CN：SH2]）有效，但对番茄黄化叶卷西西里病毒（TYLCSV）和叶蝉传播的甜菜卷叶病毒（BCTV）无效。通过共感染实验，我们发现，TYLCV的Rep/C1蛋白的瞬时表达，而非TYLCSV的，在共表达Ty-2基因的烟草原生质体植物中触发了超敏反应（HR）。我们的结果表明，TYLCV-IL的Rep/C1基因呈现出由Ty-2介导的抗性所决定的非致病性决定因子。