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 the survival of seed plants in natural environment. In rice, coleoptile elongation facilitates seedling emergence and establishment, and ethylene plays an important role in this process. However, the regulatory mechanism underlying remains largely unclear. Here, we report that ethylene promotes cell elongation and inhibits cell expansion in rice coleoptiles, resulting in longer and thinner coleoptile to facilitate seedling emergence from the soil. Transcriptome analysis showed that genes related to reactive oxygen species (ROS) generation were up-regulated and genes involved in ROS scavenging were down-regulated in the coleoptile of ethylene signaling mutants. Further investigations showed that soil coverage promotes the accumulation of ETHYLENE INSENSITIVE 3-LIKE 1 (OsEIL1) and OsEIL2 in the upper region of coleoptile, and both OsEIL1 and OsEIL2 could directly bind to the promoters of GDP-mannose pyrophosphorylase (VTC1) OsVTC1-3, peroxidase (PRX) genes OsPRX37, OsPRX81, OsPRX82, and OsPRX88 to activate their expression, leading to increased ascorbic acid (AsA) content and peroxidase activity and decreased ROS accumulation in the upper region of coleoptile. Disrupting ROS accumulation promotes coleoptile growth and seedling emergence from soil. Thus, our findings deepen our understanding of the role of ethylene and ROS in controlling coleoptile growth, and this knowledge can be used by breeders to cultivate rice varieties suitable for direct-seeding.