Pik1, an AGC kinase, positively regulates basal defense via ROS signaling in rice.

Abstract

To investigate whether the kinase activity of Pti1a is required for the regulation of defense signaling, we made amino acid substitution (T233A) of Pti1a which is a major phosphorylation site by Pti1a-interacting kinase1 (Pik1). Pti1a^T233A complements ospti1a mutant phenotypes including cell death induction, PR1b gene expression and broad resistance to rice blast. Furthermore, 35S:Pti1a^T233A transgenic lines exhibited the enhanced susceptibility against compatible race of bacterial blight. These results indicated that the phosphorylation of Thr-233 of Pti1a is important for induction of basal resistance. To investigate the Pti1a regulatory system, we characterized Pik1 which functions upstream of Pti1a. The Pik1 expression was observed in peripheral region of HR after inoculation of Magnaporthe grisea. Pik1 was transiently phosphorylated 10 minutes after treatment of H₂O₂, suggesting that Pik1 functions at the early stage of ROS signaling in disease resistance.