ABSTRACT
Plant pathogens alter the course of plant developmental processes, resulting in abnormal morphology in infected host plants. Phytoplasmas are unique plant-pathogenic bacteria that transform plant floral organs into leaf-like structures and cause the emergence of secondary flowers. These distinctive symptoms have attracted considerable interest for many years. Here, we revealed the molecular mechanisms of the floral symptoms by focusing on a phytoplasma-secreted protein, PHYL1, which induces morphological changes in flowers that are similar to those seen in phytoplasma-infected plants. PHYL1 is a homolog of the phytoplasmal effector SAP54 that also alters floral development. Using yeast two-hybrid and in planta transient co-expression assays, we found that PHYL1 interacts with and degrades the floral homeotic MADS domain proteins SEPALLATA3 (SEP3), APETALA1 (AP1) and CAULIFLOWER (CAL). This degradation of MADS domain proteins was dependent on the ubiquitin-proteasome pathway. The expression of floral development genes downstream of SEP3 and AP1 was disrupted in 35S::PHYL1 transgenic plants. PHYL1 was genetically and functionally conserved among other phytoplasma strains and species. We designate PHYL1, SAP54 and their homologs as members of the phyllody-inducing gene family of 'phyllogens'.
Subject(s)
Arabidopsis Proteins/metabolism , Bacterial Proteins/metabolism , Flowers/metabolism , MADS Domain Proteins/metabolism , Phytoplasma/metabolism , Plant Leaves/metabolism , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Bacterial Proteins/genetics , Base Sequence , Flowers/genetics , Flowers/ultrastructure , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Host-Pathogen Interactions , Immunoblotting , MADS Domain Proteins/genetics , Microscopy, Confocal , Microscopy, Electron, Scanning , Molecular Sequence Data , Phytoplasma/genetics , Plant Leaves/genetics , Plant Leaves/ultrastructure , Plants, Genetically Modified , Protein Binding , Proteolysis , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Transcription Factors/genetics , Transcription Factors/metabolism , Two-Hybrid System TechniquesABSTRACT
Systemic necrosis is one of the most severe symptoms caused by plant RNA viruses. Recently, systemic necrosis has been suggested to have similar features to a defense response referred to as the hypersensitive response (HR), a form of programmed cell death. In virus-infected plant cells, host intracellular membrane structures are changed dramatically for more efficient viral replication. However, little is known about whether this replication-associated membrane modification is the cause of the symptoms. In this study, we identified an amino-terminal amphipathic helix of the helicase encoded by Radish mosaic virus (RaMV) (genus Comovirus) as an elicitor of cell death in RaMV-infected plants. Cell death caused by the amphipathic helix had features similar to HR, such as SGT1-dependence. Mutational analyses and inhibitor assays using cerulenin demonstrated that the amphipathic helix-induced cell death was tightly correlated with dramatic alterations in endoplasmic reticulum (ER) membrane structures. Furthermore, the cell death-inducing activity of the amphipathic helix was conserved in Cowpea mosaic virus (genus Comovirus) and Tobacco ringspot virus (genus Nepovirus), both of which are classified in the family Secoviridae. Together, these results indicate that ER membrane modification associated with viral intracellular replication may be recognized to prime defense responses against plant viruses.
Subject(s)
Comovirus/enzymology , Nicotiana/virology , Plant Diseases/virology , Raphanus/virology , Amino Acid Sequence , Cell Death , Cerulenin/pharmacology , Comovirus/genetics , Comovirus/physiology , DNA Helicases/genetics , DNA Helicases/metabolism , Endoplasmic Reticulum/metabolism , Genes, Reporter , Intracellular Membranes/metabolism , Molecular Sequence Data , Mutagenesis, Site-Directed , Necrosis , Plant Leaves/cytology , Plant Leaves/physiology , Plant Leaves/virology , Protein Structure, Secondary , Recombinant Fusion Proteins , Sequence Alignment , Nicotiana/cytology , Nicotiana/drug effects , Nicotiana/physiology , Viral Proteins/genetics , Viral Proteins/metabolism , Virus ReplicationABSTRACT
Cinchona alkaloids are effective additives for enantioselective O-H insertion of alpha-phenyldiazoacetate and water by rhodium(II) complexes. Addition of silica gel promotes O-H insertion in the reaction rate and the reaction proceeds smoothly at less than the freezing point of water, e.g., -10 degrees C, and provided mandelate in up to 50% ee. The results reported here are the highest asymmetric inductions obtained to date for O-H insertions via a Rh-carbenoid.