The Sw5a gene confers resistance to ToLCNDV and triggers an HR response after direct AC4 effector recognition.

Abstract

Several attempts have been made to identify antiviral genes against <i>Tomato leaf curl New Delhi virus</i> (ToLCNDV) and related viruses. This has led to the recognition of <i>Ty</i> genes (<i>Ty1-Ty6</i>), which have been successful in developing virus-resistant crops to some extent. Owing to the regular appearance of resistance-breaking strains of these viruses, it is important to identify genes related to resistance. In the present study, we identified a ToLCNDV resistance (<i>R</i>) gene, <i>SlSw5a</i>, in a ToLCNDV-resistant tomato cultivar, H-88-78-1, which lacks the known <i>Ty</i> genes. The expression of <i>SlSw5a</i> is controlled by the transcription factor SlMyb33, which in turn is regulated by microRNA159 (sly-miR159). Virus-induced gene silencing of either <i>SlSw5a</i> or <i>SlMyb33</i> severely increases the disease symptoms and viral titer in leaves of resistant cultivar. Moreover, in <i>SlMyb33-</i>silenced plants, the relative messenger RNA level of <i>SlSw5a</i> was reduced, suggesting SlSw5a is downstream of the sly-miR159-SlMyb33 module. We also demonstrate that SlSw5a interacts physically with ToLCNDV-AC4 (viral suppressor of RNA silencing) to trigger a hypersensitive response (HR) and generate reactive oxygen species at infection sites to limit the spread of the virus. The "RTSK" motif in the AC4 C terminus is important for the interaction, and its mutation completely abolishes the interaction with Sw5a and HR elicitation. Overall, our research reports an <i>R</i> gene against ToLCNDV and establishes a connection between the upstream miR159-Myb33 module and its downstream target Sw5a to activate HR in the tomato, resulting in geminivirus resistance.