RT Journal Article SR Electronic T1 Variation and inheritance of the Xanthomonas gene cluster required for activation of XA21-mediated immunity JF bioRxiv FD Cold Spring Harbor Laboratory SP 149930 DO 10.1101/149930 A1 Furong Liu A1 Megan McDonald A1 Benjamin Schwessinger A1 Anna Joe A1 Rory Pruitt A1 Teresa Erickson A1 Xiuxiang Zhao A1 Valley Stewart A1 Pamela C. Ronald YR 2018 UL http://biorxiv.org/content/early/2018/10/19/149930.abstract AB The rice XA21-mediated immune response is activated upon recognition of the RaxX peptide produced by the bacterium Xanthomonas oryzae pv. oryzae (Xoo). The 60 residue RaxX precursor is posttranslationally modified to form a sulfated tyrosine peptide that shares sequence and functional similarity with the plant sulfated tyrosine (PSY) peptide hormones. The five kb raxX-raxSTAB gene cluster of Xoo encodes RaxX, the RaxST tyrosylprotein sulfotransferase, and the RaxA and RaxB components of a predicted type one secretion system. The identified the complete raxX-raxSTAB gene cluster is present only in Xanthomonas spp., in five distinct lineages in addition to X. oryzae. The phylogenetic distribution of the raxX-raxSTAB gene cluster is consistent with the occurrence of multiple lateral transfer events during Xanthomonas speciation. RaxX variants representing each of the five lineages, and three Xoo RaxX variants, fail to activate the XA21-mediated immune response yet retain peptide hormone activity. These RaxX variants contain a restricted set of missense mutations, consistent with the hypothesis that selection acts to maintain peptide hormone-like function. These observations are also consistent with the hypothesis that the XA21 receptor evolved specifically to recognize Xoo RaxX.