A Cytosolic Triosephosphate Isomerase Is a Key Component in XA3/XA26-Mediated Resistance

Bacterial blight caused by Xanthomonas oryzae pv oryzae (Xoo) causes severe damage to rice (Oryza sativa) production worldwide. The major disease resistance gene, Xa3/Xa26, confers broad-spectrum and durable resistance to Xoo at both seedling and adult stages. However, the molecular mechanism of the Xa3/Xa26-initiated defense pathway against Xoo is still largely unknown. Here, we show that a triosephosphate isomerase (TPI), OsTPI1.1, is a key component in XA3/XA26-mediated resistance to Xoo. OsTPI1.1 is a glycolytic enzyme that catalyzes the reversible interconversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. Transcriptional suppression of OsTPI1.1 in plants harboring Xa3/Xa26 largely impaired the XA3/ XA26-mediated resistance to Xoo, and constitutive overexpression of OsTPI1.1 in susceptible rice plants without Xa3/Xa26 only slightly decreased the susceptibility to Xoo. Therefore, both XA3/XA26 and OsTPI1.1 are required in XA3/XA26-mediated resistance. We show that OsTPI1.1 participates in the resistance through its enzymatic activity, which was enhanced significantly by its binding with XA3/XA26. Reactive oxygen species (ROS), especially hydrogen peroxide, accumulated in the OsTPI1.1overexpressing plants, and suppression of OsTPI1.1 decreased ROS accumulation. The changes in ROS are associated with the reduction of NADP(+) to NADPH, which may act as a redox cofactor to scavenge ROS, leading to reduced resistance to Xoo. These results suggest that OsTPI1.1 modulates ROS production as a resistance mechanism against Xoo.