The leaf transcriptome response to ozone mainly involves genes regulated during development in hybrid poplar

Tropospheric ozone (O₃) harms vegetation by reducing tree biomass and crop yield. Accurate risk assessment based on O₃ uptake depends on quantifying the plant's capacity to cope with O₃-generated reactive oxygen species (ROS) at the cellular level. Young leaves were shown to have better ability than mature leaves to deal with O₃ exposure but the mechanisms behind remain unclear. The aim of this study was to assess the crosstalk between O₃ response and leaf development. Time-course response to O₃ concentrations (0, 80 and 100 ppb) was studied at transcriptome and cellular level in a growing leaf (GL) and an expanded leaf (EL) of young poplar trees. The emergence of hypersensitive response-like lesions and the loss of chlorophyll content induced by O₃ was less pronounced in GL than EL showing a higher tolerance of GL to O₃. The leaf transcriptome response to O₃ involved many genes (15,784) mainly involved in leaf development resulting in a stress-induced acceleration of leaf aging and senescence. In addition to detoxification mechanisms, O₃ tolerance at early stages of leaf development might result from an insensitivity to senescence induction though further validation is needed. Understanding this process could offer new perspectives for O₃ tolerance improvement or assessment.