OsSDS is essential for DSB formation in rice meiosis

Abstract

SDS is a meiosis specific cyclin-like protein and required for DMC1 mediated double-strand break (DSB) repairing in Arabidopsis. Here, we found its rice homolog, OsSDS, is essential for meiotic DSB formation. The Ossds mutant is normal in vegetative growth but both male and female gametes are inviable. The Ossds meiocytes exhibit severe defects in homologous pairing and synapsis. No γH2AX immunosignals in Ossds meiocytes together with the suppression of chromosome fragmentation in Ossds-1 Osrad51c, both provide strong evidences that OsSDS is essential for meiotic DSB formation. Immunostaining investigations revealed that meiotic chromosome axes are normally formed but both SC installation and localization of recombination elements are failed in Ossds. We suspected that this cyclin protein has been differentiated pretty much between monocots and dicots on its function in meiosis.

Keywords: DSB formation; OsSDS; meiosis; rice.

Figure 1

Gene structure of OsSDS and sequence alignment of SDS proteins. (A) Schematic of representation of gene structure and three mutation sites in OsSDS. Exons are represented by black boxes, intones are represented by black lines, 5′UTR and 3′UTR are represented by gray boxes. The capitalized bases in sequences of wild type and mutants represent accurate mutation sites of the three allelic mutants. (B) Multiple alignment of SDS protein sequences from different organisms. The numbers at the left of the sequences are the amino acid numbers. The black boxes represent identical sequences; the dark gray boxes represent conservative sequences; the light gray boxes represent weakly similar sequences. A predicted cyclin box fold domain (276–366 amino acids) and a predicted cyclin C-terminal domain (378–419 amino acids) are underlined.

Figure 2

Male meiosis of the wild type. (A) Pachytene; (B) Diakinesis; (C) Metaphase I; (D) Anaphase I; (E) Dyad; (F) Tetrad. Chromosomes stained with 4,6-diamidino-2-phenylindole (DAPI). Bars = 5 μm.

Figure 3

Male meiosis of the Ossds-1 mutant. (A) Pachytene; (B) Diakinesis; (C) Metaphase I; (D) Anaphase I; (E) Dyad; (F) Tetrad. Chromosomes stained with DAPI. Bars = 5 μm.

Figure 4

Immunostaining of γ-H2AX at zygotene in the wild type and Ossds-1 mutant. OsREC8 signals were used to indicate the chromosome axes. Bars = 5 μm.

Figure 5

Comparison of chromosome behaviors between Osrad51c and the Ossds-1 Osrad51c double mutant. Chromosomes were stained with DAPI. Bars = 5 μm.

Figure 6

Dual immunostaining detection of several meiotic proteins in the Ossds-1. (A) OsREC8 (red) and PAIR2 (green) signals at late zygotene; (B) OsREC8 (red) and PAIR3 (green) signals at pachytene; (C) OsREC8 (red) and ZEP1 (green) signals at pachytene. Bars = 5 μm.

Figure 7

Immunostaining detection of three ZMM proteins in the wild type and Ossds-1. (A–C) Immunostaining for OsMSH5, OsMER3, and OsZIP4 at zygotene in the wild type. (D–F) Immunostaining for OsMSH5, OsMER3, and OsZIP4 at zygotene in Ossds-1. OsREC8 was used indicating chromosome axes. Bars = 5 μm.