AvrRxo1, a type III effector with a polynucleotide kinase domain
This family contains AvrRxo1-ORF1 (also called AvrRxo1) which has been shown to be a type III-secreted virulence factor in Xanthomonas oryzae (Xoc) that causes bacterial leaf streak (BLS) disease in rice plants. AvrRxo1-ORF1 delivery in rice plant cells is recognized by disease resistance protein Rxo1, which triggers resistance to BLS disease. In the Xoc genome, AvrRxo1-ORF1 is adjacent to AvrRxo1-ORF2 (also called AvrRxo1-required chaperone, or Arc1) which appears to act as a molecular chaperone. AvrRxo1 has a T4 polynucleotide kinase (T4pnk) domain, while Arc1 has a kinase-binding domain with a structure that is atypical of effector-binding chaperones. AvrRxo1 and Arc1 comprise a toxin-antitoxin system similar to members of the zeta-epsilon family, with AvrRxo1 acting as the toxin.