Lysigenous aerenchyma formation in maize root is confined to cortical cells by regulation of genes related to generation and scavenging of reactive oxygen species

To adapt to waterlogging, maize (Zea mays) forms lysigenous aerenchyma in root cortex as a result of ethylene-promoted programmed cell death (PCD). Respiratory burst oxidase homolog (RBOH) gene encodes a homolog of gp91 (phox) in NADPH oxidase, and has a role in the generation of reactive oxygen species (ROS). Recently, we found that, during aerenchyma formation, RBOH was up-regulated in all maize root tissues examined, whereas an ROS scavenging-related metallothionein (MT) gene was down-regulated specifically in cortical cells. Together, these changes should lead to high accumulations of ROS in root cortex, thereby inducing PCD for aerenchyma formation. As further evidence of the involvement of ROS in root aerenchyma formation, the PCD was inhibited by diphenyleneiodonium (DPI), an NADPH oxidase inhibitor. Based on these results, we propose a model of cortical cell-specific PCD for root aerenchyma formation.