Over-Expression of Soybean GmSAUL1 Enhances Disease Resistance in Nicotiana tabacum

Abstract

E3 ubiquitin ligases play essential roles in plant defense responses. However, their roles in other plant species have not been investigated extensively. Here, we used a gain-of-function approach to interrogate the function of GmSAUL1 (Senescence-Associated E3 Ubiquitin Ligase 1) homologs in soybeans. Ectopic over-expression of GmSAUL1a in Nicotiana tabacum resulted in autoimmune responses that could be suppressed by high temperature, which is a hallmark of NLR (nucleotide-binding leucine-rich repeat protein)-mediated resistance. Interestingly, an elevated activation of NtMPK6, but reduced activation of NtMPK4, responding to flg22 treatment, was observed in these GmSAUL1a-over-expressing tobacco lines, suggesting that over-expressing GmSAUL1a activates immune signaling through activating NtMPK6, but suppressing NtMPK4 kinase activity. Collectively, these results demonstrated that GmSAUL1 plays a positive and pivotal role in soybean immunity that is likely governed by NLR proteins.