a Pollen number differences between four homozygous mutants (rdp1-1/rdp1-1, rdp1-2/rdp1-2, rdp1-3/rdp1-3, and rdp1-4/rdp1-4), wild-type (RDP1/RDP1), and the complemented lines (rdp1-1/rdp1-1 + RDP1). Letters a, b, c indicate significant differences, determined by nested analysis of variance (ANOVA) and post hoc Tukey test; P < 0.05 (See Supplementary Table 8 for P values). Numbers of flowers pollen-counted (left to right, as plotted): N = 132, 45, 40, 60, 135, 411. b Schematic structure of the RDP1 gene. Untranslated regions (green boxes), coding regions (yellow boxes), introns (bars), two T-DNA insertion mutants (rdp1-1, rdp1-2; open triangles), and four CRISPR/Cas9-based frameshift mutants (rdp1-3 and rdp1-4 in Col-0, rdp1-5 in Uod-1, and rdp1-6 in Bor-4 backgrounds, respectively). The box in the wild-type sequences indicates the target site for CRISPR/Cas9, and red letters in mutants show the indel mutation. c, d Representative microsporocyte images of RDP1/RDP1 (c) and rdp1-3/rdp1-3 (d) stained with aniline blue. Dark spots indicate microsporocytes. Summary of observation is depicted in e. e The number of microsporocytes was significantly lower in rdp1-3/rdp1-3 than in the wild type (Wilcoxon rank sum test, P = 2.82e–06). Numbers of anthers counted (left to right, as plotted): N = 40 and 50. f, g In situ hybridization for RDP1. Similar expression patterns were observed in four (f) and two (g) individuals. f Stage 8 floral cross section; expression is detected in sporogenous cells (Sp). g Inflorescence longitudinal section; expression is observed in the inflorescence meristem (Ifm) and young flowers. h Pollen number of wild type and null mutants in the Uod-1 (blue) and Bor-4 (yellow) accessions. Dots and error bars indicate means and standard errors of means, respectively. The mutation in Bor-4 caused a stronger reduction in pollen number than that in Uod-1 (ANOVA interaction effect P = 1.07 × 10–5, one-sided test). Boxplots a, e show center line: median; box limits: upper and lower quartiles; whiskers: not >1.5 times the interquartile range; dots: outliers. Scale bars: 50 μm. Source data underlying a, e and h are provided as a Source Data file.