Figure 1.

Schematic diagram of ROS signaling for the LCD associated to the HR in a plant-pathogen interaction. (A) Recognition of an invading pathogen triggers light-dependent ROS production in chloroplasts. Chloroplast-generated ROS then signal for further ROS production in the apoplast by directly or indirectly activating RboH-type NADPH oxidases, which are involved in propagation of the signal to adjacent cells. There is also a relay of information to the nucleus and mitochondria. Altogether, the different signaling factors lead to the establishment of LCD. (B) Flavodoxin (Fld) expression in chloroplasts specifically blocks ROS generation in this organelle, delaying the appearance of LCD symptoms. This experimental evidence supports the central role played by chloroplasts in the signaling pathways for HR-associated LCD.