Rice globular embryo 4 (gle4) Mutant is Defective in Radial Pattern Formation during Embryogenesis

In higher plants, the main elements of the fundamental body plan, the apical-basal and radial patterns, are established during embryogenesis. We have isolated several globular embryo (gle) mutants of rice that fail to develop any embryonic organs. We expected that these gle mutants might include mutants defective in their radial pattern formation ability. We developed two markers specifically staining the L2 and L3 layers (OsSCR and OsPNH1, respectively) and characterized the gle mutants by using these markers in addition to the already developed markers Roc1 (marker for the L1 layer), Ramy1A (marker of the L1 layer of the epithelium), and OSH1 (marker of the apical region). One of the gle mutants, gle4, expressed Roc1 and Ramy1A at the normal positions, but other markers exhibited an abnormal expression pattern; that is, both OsPNH1 and OsSCR were expressed in the central region of the embryo and OSH1 expression was not observed. Calli from the gle4 epithelium regenerated plants with abnormal morphologies. These results indicate that the GLE4 gene is involved in radial pattern formation during rice embryogenesis to differentiate the L2 and L3 layers, but is not involved in the establishment of the L1 layer or in the formation of embryonic organs.