Activation of OsOxO2 by T-DNA Insertion Affects Plant Height and Leaf Angle in Rice

Inclination of leaf and plant height are important agronomic traits that are closely related to grain yields. Proteins involved in regulating free auxin (IAA) levels have a central role in modulating rice leaf angle and plant height. In this study, a rice mutant (named lc4) was found to have enlarged leaf angles and exhibit dwarfism compared to wild-type (WT) plants. Flanking analysis revealed that the mutation was caused by a T-DNA insertion at 270 bp upstream of the oxalate oxidase 2 (OsOxO2) ATG start codon. The insertion significantly increased the transcript levels of indole-3-acetic acid glucosyltransferase (OsIAAGLU), OsOxO1, OsOxO2 and OsOxO3 and OxO activity in lc4. Mutation of OsIAAGLU in lc4 led to partial restoration of the WT leaf angle and plant height phenotypes in iaaglu/lc4 which, however, still exhibited OxO activity comparable with that in lc4. On the other hand, mutation of OsOxO2 in lc4 also resulted in restoration of the WT leaf angle and plant height phenotypes, accompanied by reduced OxO activity and transcripts of OsIAAGLU, OsOxO1, OsOxO2 and OsOxO3. Nevertheless, overexpression of OsIAAGLU, but not OsOxO2 in the WT background, resulted in the transgenic plants showing leaf angle and plant height similar to lc4. Overexpression of OsOxO2 had no effect on the transcripts of OsIAAGLU, OsOxO1 and OsOxO3. These results suggest that activation of OsOxO2 and OsIAAGLU together resulted in altered plant architecture of lc4, while OsIAAGLU played a more direct role, OsOxO2 might be involved in regulating OsIAAGLU, OsOxO1 and OsOxO3 in a chromosome position-dependent manner.