title: The coat protein of Alfalfa mosaic virus interacts and interferes with the transcriptional activity of the bHLH transcription factor ILR3 promoting salicylic acid-dependent defence signalling response.
abstract: During virus infection, specific viral component-host factor interaction elicits the transcriptional reprogramming of diverse cellular pathways. Alfalfa mosaic virus (AMV) can establish a compatible interaction in tobacco and Arabidopsis hosts. We show that the coat protein (CP) of AMV interacts directly with transcription factor (TF) ILR3 of both species. ILR3 is a basic helix-loop-helix (bHLH) family member of TFs, previously proposed to participate in diverse metabolic pathways. ILR3 has been shown to regulate NEET in Arabidopsis, a critical protein in plant development, senescence, iron metabolism and reactive oxygen species (ROS) homeostasis. We show that the AMV CP-ILR3 interaction causes a fraction of this TF to relocate from the nucleus to the nucleolus. ROS, pathogenesis-related protein 1 (PR1) mRNAs, salicylic acid (SA) and jasmonic acid (JA) contents are increased in healthy Arabidopsis loss-of-function ILR3 mutant (ilr3.2) plants, which implicates ILR3 in the regulation of plant defence responses. In AMV-infected wild-type (wt) plants, NEET expression is reduced slightly, but is induced significantly in ilr3.2 mutant plants. Furthermore, the accumulation of SA and JA is induced in Arabidopsis wt-infected plants. AMV infection in ilr3.2 plants increases JA by over 10-fold, and SA is reduced significantly, indicating an antagonist crosstalk effect. The accumulation levels of viral RNAs are decreased significantly in ilr3.2 mutants, but the virus can still systemically invade the plant. The AMV CP-ILR3 interaction may down-regulate a host factor, NEET, leading to the activation of plant hormone responses to obtain a hormonal equilibrium state, where infection remains at a level that does not affect plant viability.
authors.affiliation: Department of Molecular and Evolutionary Plant Virology, Instituto de Biología Molecular y Celular de Plantas (IBMCP) (UPV-CSIC), Ingeniero Fausto Elio s/n, 46022, Valencia, Spain.
authors.forename: Frederic
authors.initials: F
authors.lastname: Aparicio
authors.affiliation: Department of Molecular and Evolutionary Plant Virology, Instituto de Biología Molecular y Celular de Plantas (IBMCP) (UPV-CSIC), Ingeniero Fausto Elio s/n, 46022, Valencia, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Pallás
mesh_terms: D017794:Alfalfa mosaic virus / Q000502:physiology*; D017360:Arabidopsis / Q000235:genetics / Q000276:immunology* / Q000821:virology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D036022:Capsid Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D005453:Fluorescence; D054884:Host-Pathogen Interactions; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D054883:Oxylipins / Q000378:metabolism; D010935:Plant Diseases / Q000821:virology; D011485:Protein Binding; D021381:Protein Transport; D020156:Salicylic Acid; D015398:Signal Transduction; D013194:Staining and Labeling; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism / Q000821:virology; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D036022:Capsid Proteins; D003517:Cyclopentanes; D054883:Oxylipins; D020156:Salicylic Acid; C000606190:ILR3 protein, Arabidopsis; C095691:coat protein, Alfalfa mosaic virus; C011006:jasmonic acid
keywords: AMV; ROS; coat protein; nucleolus; plant defense; transcription factors; virus-interactions