Interaction of the cauliflower mosaic virus coat protein with the pregenomic RNA leader

Using the yeast three-hybrid system, the interaction of the Cauliflower mosaic virus (CaMV) pregenomic 35S RNA (pgRNA) leader with the viral coat protein, its precursor, and a series of derivatives was studied. The purine-rich domain in the center of the pgRNA leader was found to specifically interact with the coat protein. The zinc finger motif of the coat protein and the preceding basic domain were essential for this interaction. Removal of the N-terminal portion of the basic domain led to loss of specificity but did not affect the strength of the interaction. Mutations of the zinc finger motif abolished not only the interaction with the RNA but also viral infectivity. In the presence of the very acidic C-terminal domain, which is part of the preprotein but is not present in the mature CP, the interaction with the RNA was undetectable.     

A VIGS screen identifies immunity in the Arabidopsis Pla‐1 accession to viruses in two different genera of the Geminiviridae

Geminiviruses are DNA viruses that cause severe crop losses in different parts of the world, and there is a need for genetic sources of resistance to help combat them. Arabidopsis has been used as a source for virus‐resistant genes that derive from alterations in essential host factors. We used a virus‐induced gene silencing (VIGS) vector derived from the geminivirus Cabbage leaf curl virus (CaLCuV) to assess natural variation in virus–host interactions in 190 Arabidopsis accessions. Silencing of CH‐42, encoding a protein needed to make chlorophyll, was used as a visible marker to discriminate asymptomatic accessions from those showing resistance. There was a wide range in symptom severity and extent of silencing in different accessions, but two correlations could be made. Lines with severe symptoms uniformly lacked extensive VIGS, and lines that showed attenuated symptoms over time (recovery) showed a concomitant increase in the extent of VIGS. One accession, Pla‐1, lacked both symptoms and silencing, and was immune to wild‐type infectious clones corresponding to CaLCuV or Beet curly top virus (BCTV), which are classified in different genera in the Geminiviridae. It also showed resistance to the agronomically important Tomato yellow leaf curl virus (TYLCV). Quantitative trait locus mapping of a Pla‐1 X Col‐0 F₂ population was used to detect a major peak on chromosome 1, which is designated gip‐1 (geminivirus immunity Pla‐1‐1). The recessive nature of resistance to CaLCuV and the lack of obvious candidate genes near the gip‐1 locus suggest that a novel resistance gene(s) confers immunity.     

The rice tungro bacilliform virus gene II product interacts with the coat protein domain of the viral gene III polyprotein

Rice tungro bacilliform virus (RTBV) is a plant pararetrovirus whose DNA genome contains four genes encoding three proteins and a large polyprotein. The function of most of the viral proteins is still unknown. To investigate the role of the gene II product (P2), we searched for interactions between this protein and other RTBV proteins. P2 was shown to interact with the coat protein (CP) domain of the viral gene III polyprotein (P3) both in the yeast two-hybrid system and in vitro. Domains involved in the P2-CP association have been identified and mapped on both proteins. To determine the importance of this interaction for viral multiplication, the infectivity of RTBV gene II mutants was investigated by agroinoculation of rice plants. The results showed that virus viability correlates with the ability of P2 to interact with the CP domain of P3. This study suggests that P2 could participate in RTBV capsid assembly.