SCF in Male Gametogenesis Figure 2. Pollen phenotype of fbl17 mutants and FBL17 expression during male gametogenesis. fbl17 (A) and wild type (B) mature pollen viability test by coloration with Alexander’s stain. The purple staining indicates that the grains are viable. Dehiscent pollen of qrt1-12/2 (C) and qrt1- 12/2, fbl17-1+/2 (D) stained with DAPI and observed under UV fluorescence. The four pollen grains of the tetrad show two densely stained sperm cell nuclei and one large diffuse vegetative cell nuclei in qrt-1 mutants, whereas two pollen grains of the tetrad show only a single germ cell nuclei in qrt1- 1,fbl17-1+/2 double mutants. (E, F) transmitted light picture of C and D. (G–L) Expression of the HT10 gene in the fbl17 mutant pollen. Expression of the HTR10-mRFPprotein under the HTR10 promoter in fbl17-1 (H) and wild type (K) pollen, counterstained with DAPI (G, fbl17-1; J, wild type). (I, L) transmitted light pictures of G and J. (A, B) bar = 100 mm; (C–L) bar = 10 mm. (M–U) Promoter-GUS analysis of FBL17 expression in pollen. (M, P, S) DAPI staining is applied to reveal the developmental stage of the pollen grain. (N–U) X-Gluc histochemical staining of pFBL17:GUS (N, Q, F) and non- transformed Col-0 (O, R, U) pollen grains. Bars = 10 mm (V) DNA content measurement of wild type germinative cell nuclei at prophase (n = 9; DNA = 2C), wild type sperm cell nuclei at telophase (n = 16), WT sperm cell nuclei at anthesis (n = 111) in comparison to the unique germ-cell like nuclei of fbl17 pollen (n = 77). Error bars = standard error mean. doi:10.1371/journal.pone.0004780.g002 PLoS ONE | www.plosone.org 4 March 2009 | Volume 4 | Issue 3 | e4780