p24G1 Encoded by Grapevine Leafroll-Associated Virus 1 Suppresses RNA Silencing and Elicits Hypersensitive Response-Like Necrosis in Nicotiana Species.

Grapevine leafroll-associated virus 1 (GLRaV-1) is a major pathogen associated with grapevine leafroll disease. However, the molecular mechanisms underlying GLRaV-1 interactions with plant cells are unclear. Using Agrobacterium infiltration-mediated RNA-silencing assays, we demonstrated that GLRaV-1 p24 protein (p24G1) acts as an RNA-silencing suppressor (RSS), inhibiting local and systemic RNA silencing. Electrophoretic mobility shift assays showed that p24G1 binds double-stranded 21-nucleotide small interfering RNA (siRNA), and that siRNA binding is required but not sufficient for its RSS activity. p24G1 localizes in the nucleus and can self-interact through its amino acid 10 to 210 region. Dimerization is needed for p24G1 interaction with importin α1 before moving to the nucleus, but is not required for its siRNA binding and RSS activity. Expression of p24G1 from a binary pGD vector or potato virus X-based vector elicited a strong hypersensitive response in Nicotiana species, indicating that p24G1 may be a factor in pathogenesis. Furthermore, p24G1 function in pathogenesis required its RSS activity, dimerization and nuclear localization. In addition, the region of amino acids 122-139 played a crucial role in the nuclear import, siRNA binding, silencing suppression and pathogenic activity of p24G1. These results contribute to our understanding of the molecular mechanisms underlying GLRaV-1 infection.

Complete nucleotide sequence of a Chinese isolate of Grapevine leafroll-associated virus 3 reveals a 5' UTR of 802 nucleotides.

Grapevine leafroll-associated virus 3 (GLRaV-3) is widely spread in China. Here we report, for the first time, the complete nucleotide sequence of the Chinese isolate (LN) of GLRaV-3. The 18,563-nt genomic RNA is the largest of the GLRaV-3 genomes reported to date, with a 5' untranslated region of 802 nt. Its sequence shares 87.99-98.15 % identity with those of previously reported isolates, and phylogenetic analysis suggested placing isolate LN in group 3, together with another fully sequenced isolate, PL-20.

HC-Pro protein of sugar cane mosaic virus interacts specifically with maize ferredoxin-5 in vitro and in planta.

Symptom development of a plant viral disease is a result of molecular interactions between the virus and its host plant; thus, the elucidation of specific interactions is a prerequisite to reveal the mechanism of viral pathogenesis. Here, we show that the chloroplast precursor of ferredoxin-5 (Fd V) from maize (Zea mays) interacts with the multifunctional HC-Pro protein of sugar cane mosaic virus (SCMV) in yeast, Nicotiana benthamiana cells and maize protoplasts. Our results demonstrate that the transit peptide rather than the mature protein of Fd V precursor could interact with both N-terminal (residues 1-100) and C-terminal (residues 301-460) fragments, but not the middle part (residues 101-300), of HC-Pro. In addition, SCMV HC-Pro interacted only with Fd V, and not with the other two photosynthetic ferredoxin isoproteins (Fd I and Fd II) from maize plants. SCMV infection significantly downregulated the level of Fd V mRNA in maize plants; however, no obvious changes were observed in levels of Fd I and Fd II mRNA. These results suggest that SCMV HC-Pro interacts specifically with maize Fd V and that this interaction may disturb the post-translational import of Fd V into maize bundle-sheath cell chloroplasts, which could lead to the perturbation of chloroplast structure and function.