OsEIL1 and OsEIL2, Two Master Regulators of Rice Ethylene Signaling, Promote the Expression of ROS Scavenging Genes to Facilitate Coleoptile Elongation and Seedling Emergence from Soil

Successful emergence from the soil is a prerequisite for survival of germinating seeds in their natural environment. In rice, coleoptile elongation facilitates seedling emergence and establishment, and ethylene plays an important role in this process. However, the underlying regulatory mechanism remains largely unclear. Here, we report that ethylene promotes cell elongation and inhibits cell expansion in rice coleoptiles, resulting in longer and thinner coleoptiles that facilitate seedlings emergence from the soil. Transcriptome analysis showed that genes related to reactive oxygen species (ROS) generation are upregulated and genes involved in ROS scavenging are downregulated in the coleoptiles of ethylene-signaling mutants. Further investigations showed that soil coverage promotes accumulation of ETHYLENE INSENSITIVE 3-LIKE 1 (OsEIL1) and OsEIL2 in the upper region of the coleoptile, and both OsEIL1 and OsEIL2 can bind directly to the promoters of the GDP-mannose pyrophosphorylase (VTC1) gene OsVTC1-3 and the peroxidase (PRX) genes OsPRX37, OsPRX81, OsPRX82, and OsPRX88 to activate their expression. This leads to increased ascorbic acid content, greater peroxidase activity, and decreased ROS accumulation in the upper region of the coleoptile. Disruption of ROS accumulation promotes coleoptile growth and seedling emergence from soil. These findings deepen our understanding of the roles of ethylene and ROS in controlling coleoptile growth, and this information can be used by breeders to produce rice varieties suitable for direct seeding.