Isolation and functional characterization of a gene involved in cell elongation of rice roots

Root length is one of the important parameters of root traits directly related to uptake of water and nutrients, however, the molecular mechanisms controlling root length are still not fully understood. Here, we isolated a mutant, dice2 (defective in cell elongation 2) of rice (Oryza sativa) showing short roots. The cell length rather than the cell width of the roots was decreased in the mutant, but the root function in mineral element uptake was hardly altered. Furthermore, there was no alteration in the root anatomy of the mutant compared with the wild-type rice. Intriguingly, the root growth defect in the mutant could be partially rescued by high temperature. The mutant accumulated more H2O2, but less O2.- in the roots at low temperature, but at similar level at high temperature compared with the wild-type rice. A map-based cloning combined with complementation test revealed that the short-root phenotype was caused by a nucleotide substitution of a gene, which was annotated to encode Lysine Ketoglutarate Reductase Trans-Splicing related 1 (OsLKRT1). OsLKRT1 encodes a cytosol-localized protein and was expressed in both the roots and shoots. Furthermore, OsLKRT1 was expressed in all cells of the root tip and root elongation regions. RNA-seq analysis showed that there was no difference in the expression level of genes involved in root development identified so far. These results indicate that the gene identified in this study is involved in novel pathway required for cell elongation of the roots in rice although its exact role remains to be further investigated.