Table_8_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）是由白粉虱传播的一种极具破坏力的栽培番茄病毒。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的引入系线存在较大倒位，这严重抑制了重组，至今阻碍了Ty-2的克隆。在本研究中，我们报告了利用Ty-2引入系线与多个易感S. habrochaites品系之间的杂交进行精细定位和克隆Ty-2。研究发现，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，从而实现标记辅助选择。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，但对番茄黄化叶卷萨丁尼亚病毒（TYLCSV）和叶蝉传播的甜菜卷叶病毒（BCTV）无效。通过共侵染实验，我们发现，TYLCV的Rep/C1蛋白的瞬时表达，而非TYLCSV，在共表达Ty-2基因的拟南芥（Nicotiana benthamiana）植株中触发了过敏反应（HR）。我们的研究结果表明，TYLCV-IL的Rep/C1基因呈现了Ty-2介导抗性的无毒决定因子。