Autophagy-Like Cell Death Regulates Hydrogen Peroxide and Calcium Ion Distribution in Xa3/Xa26-Mediated Resistance to Xanthomonas oryzae pv. oryzae

Abstract

The broad-spectrum and durable resistance gene <i>Xa3/Xa26</i> against <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) has been widely exploited in rice production in China. But the cytological features of the <i>Xa3/Xa26-</i>mediated resistance reaction have been rarely reported. This study reveals the cytological characteristics of the <i>Xa3/Xa26</i>-mediated resistance reaction against <i>Xoo</i> to uncover the functions of hypersensitive response programmed cell death (HR-PCD) in rice. Autophagy-like cell death, which was characterized by double-membrane bodies appearance in xylem parenchyma cell and mesophyll cell, was inhibited by autophagy inhibitor 3-methyladenin (3-MA). The autophagy-related genes were induced to reach a high level in resistance reaction. The hydrogen peroxide (H₂O₂) maintained a low concentration on the plasma membrane. The calcium ions localized on the apoplast were transferred into the vacuole. The autophagy inhibitor (3-MA) impaired <i>Xa3/Xa26-</i>mediated resistance by promoting the accumulation of H₂O₂, and inhibited the transfer of extracellular calcium ions into the vacuole in the xylem parenchyma cells and mesophyll cells. Therefore, the HR-PCD belongs to autophagy-like cell death in the <i>Xa3/Xa26-</i>mediated resistance reaction. These results suggest that the autophagy-like cell death participates in the <i>Xa3/Xa26</i>-mediated resistance by negatively regulating H₂O₂ accumulation, in order to abolish oxidative stress and possibly activate calcium ion signals in xylem parenchyma cells of the rice leaf.