The Rice Bacterial Blight Resistance Gene xa5 Encodes a Novel Form of Disease Resistance

The rice xa5 gene for disease resistance to Xanthomonas oryzae pv. oryzae has been positionally cloned and encodes the gamma subunit of transcription factor IIA (TFIIAgamma). TFIIAgamma is a general eukaryotic transcription factor with no previously known role in disease resistance. xa5 is unusual in that it is recessive and does not conform to one of the typical resistance gene structural classes. Sequencing of TFIIAgamma in resistant and susceptible isolines revealed two nucleotide substitutions resulting in an amino acid change between resistant and susceptible cultivars. This association was conserved across 27 resistant and nine susceptible rice lines in the Aus-Boro group.