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Complete genome sequence of Xanthomonas phaseoli pv. phaseoli G66 reveals a particular repertoire of Type 3 effectors including a novel TAL effector

Lulu Cai: University of Florida

<div><em>Xanthomonas phaseoli</em> pv.<em> phaseoli</em> (Xpp) and <em>Xanthomonas citri</em> pv. <em>fuscans </em>(Xcf) are the causal agents of common bacterial blight (CBB). Strains of both species cause systemic and nearly identical disease symptoms on bean. We determined the complete genome sequence of Xpp U.S. strain G66 through PACBIO sequencing. This genome carries a 5,031,159 bp chromosome and three plasmids of 6,364 bp, 50,429 bp and 37,769 bp. G66 shows a 99.9% Average Nucleotide Identity (ANI) to previously sequenced Xpp strain CFBP412 (Ruh et al, 2017), suggesting a common ancestor. The entire effector repertoire of G66 was compared against Xcf, revealing 18 effectors that are common to both Xcf and Xpp, seven effectors that are unique to Xcf, and four unique to Xpp: XopAP, XopAU, XopAV and HpaA. Among the common Xcf and Xpp effectors were transcription activator-like (TAL) effectors of the <em>pthA/avrBs3</em> gene family and found in all CBB strains examined. These TAL effectors are required for both cotton blight and citrus canker disease caused by different subspecies or pathovars of <em>X. citri</em>. Such TAL effectors are found in many different xanthomonads, and are often found in all strains causing a particular disease phenotype. G66 carries two potential <em>pthA/avrBs3</em> homologs on two different plasmids but only one appears intact. This homolog carries 19 direct repeats and is currently being functionally analyzed.</div>