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 yel-low 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 Hok-kaido, 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 investi-gate how LYSV with S-type P1 (LYSV-S) could have invaded LYSV with N-type P1 (LYSV-N)-infected gar-lic, 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 Al-liumspp. compared to LYSV-N. Because P1 proteins of potyviruses have been reported to promote RNA silenc-ing 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, sug-gesting 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.

Automated summary

The length of the P1 protein of leek yellow stripe virus (LYSV) isolates in Japan varies, with the S-type P1 being shorter than the N-type P1. Both N-type and S-type P1 sequences can be found in mixed infections in garlic fields in Hokkaido. LYSV-S is detected more frequently in Allium spp. plants other than garlic in Honshu, suggesting a wider host range compared to LYSV-N. The P1 protein of LYSV has RNA silencing suppressor (RSS) activity, with the S-type P1 showing stronger RSS activity than the N-type P1.