The Role of RaxST, a Prokaryotic Sulfotransferase, and RaxABC, a Putative Type I Secretion System, in Activation of the Rice XA21-Mediated Immune Response

Figure 1

Working model for the synthesis and secretion of proteins required for activation of XA21-mediated immunity (encoded by rax genes). In this model, the adenosine-5′-triphosphate (ATP) sulfurylase RaxP and the adenosine-5′-phosphosulfate (APS) kinase RaxQ catalyze the production of the universal sulfuryl group donor 3′-phosphoadenosine 5′-phosphosulfate (PAPS). The RaxST sulfotransferase utilizes PAPS as a substrate. We hypothesize that RaxST sulfates a molecule that contains a leader peptide, which is cleaved by the peptidase domain of the RaxB protein and secreted outside the bacterial cell by the RaxABC T1SS.