The Agrobacterium F-Box Protein Effector VirF Destabilizes the Arabidopsis GLABROUS1 Enhancer/Binding Protein-Like Transcription Factor VFP4, a Transcriptional Activator of Defense Response Genes.

Agrobacterium-mediated genetic transformation not only represents a technology of choice to genetically manipulate plants, but it also serves as a model system to study mechanisms employed by invading pathogens to counter the myriad defenses mounted against them by the host cell. Here, we uncover a new layer of plant defenses that is targeted by A. tumefaciens to facilitate infection.

Interaction of Arabidopsis Trihelix-Domain Transcription Factors VFP3 and VFP5 with Agrobacterium Virulence Protein VirF.

Agrobacterium is a natural genetic engineer of plants that exports several virulence proteins into host cells in order to take advantage of the cell machinery to facilitate transformation and support bacterial growth. One of these effectors is the F-box protein VirF, which presumably uses the host ubiquitin/proteasome system (UPS) to uncoat the packaging proteins from the invading bacterial T-DNA. By analogy to several other bacterial effectors, VirF most likely has several functions in the host cell and, therefore, several interacting partners among host proteins.

Assaying proteasomal degradation in a cell-free system in plants.

The ubiquitin-proteasome pathway for protein degradation has emerged as one of the most important mechanisms for regulation of a wide spectrum of cellular functions in virtually all eukaryotic organisms. Specifically, in plants, the ubiquitin/26S proteasome system (UPS) regulates protein degradation and contributes significantly to development of a wide range of processes, including immune response, development and programmed cell death. Moreover, increasing evidence suggests that numerous plant pathogens, such as Agrobacterium, exploit the host UPS for efficient infection, emphasizing the importance of UPS in plant-pathogen interactions.

Resistance to Tomato chlorosis virus in wild tomato species that impair virus accumulation and disease symptom expression.

Tomato chlorosis virus (ToCV) (genus Crinivirus, family Closteroviridae) is an emerging threat to tomato crops worldwide. Although symptoms on fruits are not obvious, yield losses occur through decreased fruit size and number. Control of ToCV epidemics is difficult because the virus is transmitted by several whitefly vector species and its relatively wide host range facilitates establishment in local wild reservoirs.

Synergistic Interaction Between Tomato chlorosis virus and Tomato spotted wilt virus Results in Breakdown of Resistance in Tomato.

ABSTRACT Multiple viral infections frequently are found in single plants of cultivated and wild hosts in nature, with unpredictable pathological consequences. Synergistic reactions were observed in mixed infections in tomato plants doubly infected with the positive-sense and phloem-limited single-stranded RNA (ssRNA) crinivirus Tomato chlorosis virus (ToCV) and the negative-sense ssRNA tospovirus Tomato spotted wilt virus (TSWV). Synergism in a tomato cultivar susceptible to both viruses resulted in a rapid death of plants.