Leek Yellow Stripe Virus Can Adjust for Host Adaptation by Trimming the N-Terminal Domain to Allow the P1 Protein to Function as an RNA Silencing Suppressor.

In Japan, the P1 protein (S-type) encoded by leek yellow stripe virus (LYSV) isolates detected in Honshu and southward is shorter than the P1 (N-type) of LYSV isolates from garlic grown in Hokkaido due to a large deletion in the N-terminal half. In garlic fields in Hokkaido, two types of LYSV isolate with N- and S-type P1s are sometimes found in mixed infections. In this study, we confirmed that N- and S-type P1 sequences were present in the same plant and that they belong to different evolutionary phylogenetic groups. To investigate how LYSV with S-type P1 (LYSV-S) could have invaded LYSV with N-type P1 (LYSV-N)-infected garlic, we examined wild Allium spp. plants in Hokkaido and found that LYSV was almost undetectable. On the other hand, in Honshu, LYSV-S was detected at a high frequency in Allium spp. other than garlic, suggesting that the LYSV-S can infect a wider host range of Allium spp. compared to LYSV-N. Because P1 proteins of potyviruses have been reported to promote RNA silencing suppressor (RSS) activity of HC-Pro proteins, we analyzed whether the same was true for P1 of LYSV. In onion, contrary to expectation, the P1 protein itself had RSS activity. Moreover, the RSS activity of S-type P1 was considerably stronger than that of N-type P1, suggesting that LYSV P1 may be able to enhance its RSS activity when the deletion is in the N-terminal half and that acquiring S-type P1 may have enabled LYSV to expand its host range.

在日本，本州及以南地区检测到的韭葱黄条病毒（LYSV）分离株所编码的P1蛋白（S型）由于其N端一半存在大片段缺失，比北海道种植的大蒜中LYSV分离株的P1（N型）要短。在北海道的大蒜田中，有时会在混合侵染中发现具有N型和S型P1的两种LYSV分离株。在本研究中，我们证实N型和S型P1序列存在于同一植株中，且它们属于不同的进化系统发育组。为了研究具有S型P1的LYSV（LYSV - S）是如何侵入已被具有N型P1的LYSV（LYSV - N）感染的大蒜的，我们检测了北海道的野生葱属植物，发现几乎检测不到LYSV。另一方面，在本州，在大蒜以外的葱属植物中高频检测到LYSV - S，这表明与LYSV - N相比，LYSV - S能够感染更广泛的葱属植物宿主范围。由于已报道马铃薯Y病毒属的P1蛋白可促进HC - Pro蛋白的RNA沉默抑制子（RSS）活性，我们分析了LYSV的P1是否也如此。在洋葱中，与预期相反，P1蛋白本身具有RSS活性。此外，S型P1的RSS活性明显强于N型P1，这表明当缺失位于N端一半时，LYSV P1可能能够增强其RSS活性，并且获得S型P1可能使LYSV能够扩大其宿主范围。