Loss of VPS9b enhances vps9a-2 phenotypes.

Plant innate immunity enables plants to defend themselves against infectious pathogens. While membrane trafficking and release of exosomes are considered vital for correct execution of innate immunity, the mechanisms behind remain elusive. Recently, we have shown that VPS9a, the general guanine-nucleotide exchange factor activating Rab5 GTPases, is required for both pre- and post-invasive immunity against powdery mildew fungi in Arabidopsis thaliana. Yet, the Arabidopsis genome contains a close homologue of VPS9a, which potentially plays specific roles in innate immunity. Here we show that this gene, VPS9b, while weakly expressed, contributes to regulating development and disease resistance, which is predominantly regulated by VPS9a. Based on these observations, we suggest that VPS9b has no specialized functionality, but rather is becoming a non-expressed pseudogene.