Antiviral RNAi defective 4 (AVI4) encodes a lysophospholipid acyltransferase coopting AVI2 and ATG8a to promote antiviral immunity in Arabidopsis

RNA interference (RNAi)-mediated antiviral immunity is an evolutionarily conserved mechanism preventing virus infection in eukaryotes. In our recent-year studies, a sensitized genetic screen was developed to identify antiviral RNAi-defective mutants (avi) for uncovering components in the antiviral pathway in Arabidopsis, and AVI2 was discovered as a novel regulator enhancing biogenesis of viral siRNAs (vsiRNAs) to promote the small RNA-based antiviral immunity. However, the molecular mechanisms modulating the efficiency of RNAi-mediated antiviral immunity remain largely unclear Here, we identified avi4 from the same patch of genetic screen. Mapping-by-sequencing cloned the T-DNA induced mutation in LPEAT2 gene for avi4, which was further confirmed through an allelic lpeat2 mutant and complementation analysis. LPEAT2, a lysophospholipid acyltransferase in Arabidopsis, functions to biosynthesize phospholipids (especially phosphatidylethanolamine, PE) and modulate autophagy pathway. We revealed that LPEAT2, but not its homolog LPEAT1, interacted with AVI2 to enhance RDR1/6-dependent vsiRNA biogenesis. Interestingly, we found that LPEAT2 also interacted to stabilize ATG8a, the core component of autophagy, and promote autophagy before or after viral infection. Notably, we unveiled that overexpression of ATG8a enhanced vsiRNA production and antiviral resistance, which was dependent of LPEAT2 function and could be repressed by VSR 2b. Therefore, our research discovered AVI4 (LPEAT2) as a novel regulator of RNAi-mediated antiviral immunity, and elucidated that AVI4 coopted AVI2 and ATG8a to enhance vsiRNA biogenesis for robust antiviral defense in Arabidopsis.