The miR393a/target module regulates seed germination and seedling establishment under submergence in rice (Oryza sativa L.)

The conserved miRNA393 family is thought to be involved in root elongation, leaf development and stress responses, but its role during seed germination and seedling establishment remains unclear. In this study, expression of the MIR393a/target module and its role in germinating rice (Oryza sativa L.) seeds were investigated. beta-Glucuronidase (GUS) analysis showed that MIR393a and OsTIR1 had spatial-temporal transcriptional activities in radicle roots, coleoptile tips and stomata cells, corresponding to a dynamic auxin response. miR393a promoted primary root elongation when rice seeds were germinated in air and inhibited coleoptile elongation and stomatal development when seeds were submerged. Under submergence, the expression of miR393a was inhibited, and then the auxin response was induced. In the process, OsTIR1 and OsAFB2, auxin receptor genes, were negatively regulated by miR393. We found that miR393a inhibited stomatal development and coleoptile elongation but promoted free indole acetic acid (IAA) accumulation in the rice coleoptile tips. In addition, exogenous abscisic acid (ABA) enhanced the expression of miR393 and inhibited coleoptile growth. Together, miR393a/target plays a role in coleoptile elongation and stomatal development via modulation of auxin signalling during seed germination and seedling establishment under submergence. This study provides new perspectives on the direct sowing of rice seeds in flooded paddy fields.