Type III regulators HrpG and HrpXct control synthesis of alpha-amylase, which is involved in in planta multiplication of Xanthomonas axonopodis pv. citri

HrpG and HrpXct, type III (T3) key regulators, were shown to be involved in the negative regulation of the synthesis of one of the α-amylase isozymes in Xanthomonas axonopodis pv. citri strain NA-1 by comparing the specific activity of α-amylase in two regulator mutants (hrpG ⁻ and hrpX ⁻ ) and the wild type. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that one of the α-amylase isozymes (encoded by the amy gene) is regulated by these T3 regulators. Furthermore, the Amy protein was shown to inhibit the multiplication of Xac NA-1 in the host plant.