# Natural genetic variation of a single amino acid in beet necrotic yellow vein virus P31 protein modulates evasion of plant ubiquitination-mediated antiviral immunity

## TL;DR

A single amino acid change in a beet virus protein helps it evade plant defenses, leading to increased virulence and crop damage.

## Contribution

The study identifies a natural amino acid variation in a viral protein that enables evasion of plant ubiquitination-mediated immunity.

## Key findings

- Chinese BNYVV isolates with Arg-147 in P31 show higher virulence due to evasion of HRD1-mediated degradation.
- HRD1 targets P31 with Lys-147 for ubiquitination and degradation, reducing viral infection.
- Knockout of HRD1 increases plant susceptibility to BNYVV infection.

## Abstract

Plant virus evolution frequently leads to the emergence of highly virulent strains, posing persistent threats to global crop production. However, the mechanisms by which viral evolution enables evasion of plant defense responses remain poorly understood. Here, we found that Benyvirus necrobetae (beet necrotic yellow vein virus, BNYVV), causing the most destructive rhizomania disease in sugar beet worldwide, exhibits distinct pathogenicity associated with different virus isolates. Two Chinese isolates from Inner Mongolia (NM) and Xin Jiang (XJ) exhibit significantly higher virulence than the Japanese isolate O11 and Germany isolate OW1. Moreover, the high pathogenicity is attributed to the Arg-147 residue in P31NM and P31XJ. The P31 proteins of these isolates exhibit enhanced protein stability, compared with P31O11 and P31OW1 carrying a Lys-147 residue. Furthermore, the E3 ubiquitin ligase Hmg-CoA reductase degradation 1 (HRD1) targets the P31O11 Lys-147 for ubiquitination and subsequent degradation. Whereas, the P31NM Arg-147 evades HRD1-mediated degradation, conferring a virulence advantage. Overexpression of HRD1 obviously inhibits BNYVVO11 infection, rather than BNYVVNM. Moreover, knockout of NbHRD1 in Nicotiana benthamiana enhanced susceptibility to BNYVV infection. Collectively, our findings demonstrate an ongoing evolutionary arms race, in which HRD1 is a critical antiviral component by ubiquitinating viral proteins, while natural mutations in viral genomes enable evasion of host defense.

Natural variation of plant viruses usually produces newly emerging hyper-virulent strains triggering devastating losses in crop production worldwide. However, how virus variation affects the arm race of viruses and plant immunity remains largely unknown. Here, our study mainly focused on variation of Benyvirus necrobetae (beet necrotic yellow vein virus, BNYVV), and uncovered a critical molecular arms race between point mutation of P31, a pathogenicity factor of BNYVV, and a host E3 ligase, Hmg-CoA reductase degradation 1 (HRD1). Chinese isolates from Inner Mongolia and Xin Jiang demonstrated dramatically higher virulence compared to isolates from Japanese and Germany. The reason lies in a single amino acid variation leading to unprecedented stability and pathogenicity, which enable BNYVV to evade the plant defense system. We further demonstrate that HRD1 as an E3 ligase targets and degrades the Japanese isolate, but the Inner Mongolia isolate evades this degradation. Overexpression of HRD1 effectively blocks infection by the Japanese isolate but fails to inhibit the Inner Mongolia isolate, while knocking out NbHRD1 plants became susceptible in BNYVV infection. Our finding reveals an intense, ongoing evolutionary battle at the molecular level, highlighting a rapidly shifting threat to global food security.