Multiple roles of ROS in flowering plant reproduction

Reactive oxygen species (ROS), which are generated by different cellular compartments through aerobic metabolic pathways, are generally considered to play dual roles in plants. They are toxic compounds at high concentration but are also required to modulate multiple signaling reactions and gene regulatory networks in biotic and abiotic stress responses as well as during plant growth and development. Recent studies revealed that ROS play also critical roles in various aspects of flowering plant reproduction. In male gametophytes, ROS regulate germline specification and differentiation, and they are associated with programmed cell death (PCD) of the tapetum to regulate pollen development. During female gametophyte formation, ROS are involved in cell identity determination, polarity regulation and megaspore PCD. After pollination, ROS are of vital importance for regulation of self-incompatibility responses, for pollen hydration and for successful germination on the stigma. Further roles have been reported during pollen tube growth and guidance in the transmitting tract, pollen tube reception and sperm cell release in the female gametophyte as well as during gamete fusion. In this chapter, we will provide an overview of the multiple functions of ROS signaling during plant reproductive development from germline initiation to double fertilization. We will focus on flowering plants and discuss the generation and elimination of ROS, and the induction and regulation of various downstream signaling pathways.