Fig. 1. Phenotypic, histological, and transcriptional analyses of wild-type (WT) and ossp3 mutant plants. A, Root characterization of WT, ossp3-1, and ossp3-2 over 10 d post-germination. From left to right at each time point are WT, ossp3-1, and ossp3-2. Scale bar, 1 cm. B, Primary root length of WT, ossp3-1, and ossp3-2 over 10 d post-germination. Data are mean ± SD (n = 15). C, Number of lateral roots of WT, ossp3-1, and ossp3-2 over 10 d post-germination. Data are mean ± SD (n = 15). D, Angles of lateral roots of WT, ossp3-1, and ossp3-2 at 6‒13 d post-germination. Bar chart shows lateral root angle; circles indicate differences in lateral root angles. Data are mean ± SD (n = 15). E, Transverse sections of the elongation zone of WT and ossp3-1. Scale bar, 50 μm. F, Diameter of the elongation zone of WT and ossp3-1. Data are mean ± SD (n = 3). G, Longitudinal sections of the elongation zone of WT and ossp3-1. Scale bar, 50 μm. H, Cell length and width in the elongation zone of WT and ossp3-1. Data are mean ± SD (n = 50). I, Yeast two-hybrid assay between OsSP3 and LEA5. Yeast transformants were spotted onto medium (SD/‐Leu/‐Trp) and selective medium (SD/‐Leu/‐Trp/‐His/‐Ade) supplemented with X‐α‐gal. Serial dilutions (1, 0.1, and 0.01) were applied on the selective medium. J, Bimolecular fluorescence complementation (BiFC) assay between OsSP3 and LEA5 in Nicotiana benthamiana. cYFP, C-terminal yellow fluorescent protein; nYFP, N-terminal yellow fluorescent protein. H2B-mCherry labels the nucleus. Scale bars, 20 μm. K, Split-luciferase (LUC) assays between OsSP3 and LEA5 and controls. cLUC, C-terminal LUC; nLUC, N-terminal LUC. L, Subcellular localization of LEA5 in Nicotiana benthamiana leaf cells and rice protoplasts. H2B-mCherry labels the nucleus. GFP, Green fluorescent protein. Scale bars in upper and lower panels are 50 μm and 5 μm, respectively. M, OsSP3 and LEA5 expression by qRT-PCR. Panicle and root samples were collected at the young panicle differentiation stage with three biological replicates. OsActin (Os03g0718100) was used as an internal reference. Data are mean ± SD (n = 3). * and ** indicate significant differences at P < 0.05 and P < 0.01, respectively, by Student’s t-test.