Title : Understanding defense and counter-defense in plant-virus co-evolutionary arms race and developing next generation antiviral resistance
Plants are constantly attacked by diverse pathogens including viruses. They have evolved sophisticated defense mechanisms to protect themselves from pathogen infections. For viral pathogens, nucleotide-based RNA silencing and receptor-based innate immunity that comprises PAMP (pathogen-associated molecular patterns)- triggered immunity (PTI) and effector-triggered immunity (ETI) are the primary antiviral strategies. In response, viruses have also evolved virulence strategies to suppress host defenses. RNA silencing and viral suppression of RNA silencing have been extensively investigated in the past twenty years. A number of viral suppressors of RNA silencing have been identified and their functional mechanisms have been elucidated. Although PTI- and ETI-based immunity concepts were initially developed based on molecular interactions between plants and noviral pathogens, recent evidence has suggested that these also apply to virus-plant interactions. It has been revealed that most antiviral R gene products share structural similarity with antibacterial and antifungal R proteins and elicit typical ETI response. Viral resistance breaking isolates may evade ETI to overcome R-mediated resistance through introduction of mutations into the viral elicitor. Viral replicationassociated dsRNA can trigger PTI-like responses. Recent data have shown that viruses do encode and deploy Avr factors to suppress PTI. Furthermore, viruses have ability to inhibit the NPR1 pathway, part of both PTI and ETI signaling pathways. Emerging evidence also reveals that the autophagy and unfolded protein response pathways are interlinked with the receptor-based innate immunity and play essential roles in viral infection. Thus, the co-evolutionary arms race between plants and viruses is extremely complex and aggregative. These recent findings will assist in the development of next generation antiviral resistance.