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Aberrant Meiotic Prophase I Leads to Genic Male Sterility in the Novel TE5A Mutant of Brassica napus

View Article: PubMed Central - PubMed

ABSTRACT

Genic male sterility (GMS) has already been extensively utilized for hybrid rapeseed production. TE5A is a novel thermo-sensitive dominant GMS line in Brassica napus, however, its mechanisms of GMS remain largely unclear. Histological and Transmission electron microscopy (TEM) analyses of anthers showed that the male gamete development of TE5A was arrested at meiosis prophase I. EdU uptake of S-phase meiocytes revealed that the TE5A mutant could accomplish DNA replication, however, chromosomal and fluorescence in situ hybridization (FISH) analyses of TE5A showed that homologous chromosomes could not pair, synapse, condense and form bivalents. We then analyzed the transcriptome differences between young floral buds of sterile plants and its near-isogenic fertile plants through RNA-Seq. A total of 3,841 differentially expressed genes (DEGs) were obtained, some of which were associated with homologous chromosome behavior and cell cycle control during meiosis. Dynamic expression changes of selected candidate DEGs were then analyzed at different anther developmental stages. The present study not only demonstrated that the TE5A mutant had defects in meiotic prophase I via detailed cytological analysis, but also provided a global insight into GMS-associated DEGs and elucidated the mechanisms of GMS in TE5A through RNA-Seq.

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Related in: MedlinePlus

TEM micrographs of the anthers from the wild-type (F–J) and the TE5A mutant (A–E). (A,F), early meiotic PMC stage with no detectable differences between the TE5A mutant (A) and the wild type (F); (B,G), the tetrad stage, in the wild type, the PMCs could complete meiosis I and enter the tetrad stage with tetrad formation (G), whereas no dyads or tetrads were observed in the TE5A mutant (B); (C,D,H,I), the microspore stage, microspores were released from the tetrads and covered with an microspore wall in the wild-type (H,I). However, the PMCs of the mutant did not undergo meiosis and developed into pseudo-microspores surrounded by a layer of grains, instead of a typical microspore wall (C,D); (E,J), the pollen grain stage, the wild-type microspores developed into mature pollen grains with the normal exine wall (J), whereas pseudo-microspores of the TE5A mutant were degenerated, resulting in an empty locule. T, tapetum; PMC, pollen mother cell; Tds, tetrad; Msp, microspore; Psm, pseudo-microspore; Dps, degenerating pseudo-microspore; PG: pollen grain; Scale bars = 10 μm.
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f3: TEM micrographs of the anthers from the wild-type (F–J) and the TE5A mutant (A–E). (A,F), early meiotic PMC stage with no detectable differences between the TE5A mutant (A) and the wild type (F); (B,G), the tetrad stage, in the wild type, the PMCs could complete meiosis I and enter the tetrad stage with tetrad formation (G), whereas no dyads or tetrads were observed in the TE5A mutant (B); (C,D,H,I), the microspore stage, microspores were released from the tetrads and covered with an microspore wall in the wild-type (H,I). However, the PMCs of the mutant did not undergo meiosis and developed into pseudo-microspores surrounded by a layer of grains, instead of a typical microspore wall (C,D); (E,J), the pollen grain stage, the wild-type microspores developed into mature pollen grains with the normal exine wall (J), whereas pseudo-microspores of the TE5A mutant were degenerated, resulting in an empty locule. T, tapetum; PMC, pollen mother cell; Tds, tetrad; Msp, microspore; Psm, pseudo-microspore; Dps, degenerating pseudo-microspore; PG: pollen grain; Scale bars = 10 μm.

Mentions: Analysis of paraffin-cross sections of anther sections had indicated that the early detectable defect in the TE5A mutant involved the disruption of meiosis I, which then led to a failure in dyad or tetrad generation in the anther. To further understand the abnormalities in the mutant, TEM was used to compare the differences in anther development between the mutant and wild-type plants. First, tapetal development during meiosis was normal in the TE5A mutant compared to that in the wild-type (Fig. 3). For male mate development, similar to the observations using paraffin-cross sections, no detectable differences in the early PMC stage were observed between the TE5A mutant and the wild-type (Fig. 3A,F). However, some differences in male mate development after the early PMC stage were observed between the mutant and the wild-type. In the wild-type, the PMCs completed meiosis I and entered the tetrad stage (Fig. 3G). However, at this stage, no dyads or tetrads were observed in the TE5A mutant, and only PMCs were observed (Fig. 3B). Subsequently, the wild-type microspores were released from the tetrads and were covered with a microspore wall (Fig. 3H,I), and in contrast to that observed in the wild-type, the PMCs of the mutant did not accomplish meiosis I and developed into pseudo-microspores that were surrounded by a layer of grains, instead of the a typical microspore wall (Fig. 3C,D). Finally, the wild-type microspores underwent mitosis and developed into mature pollen grains with the normal exine wall (Fig. 3J), whereas the pseudo-microspores of the TE5A mutant degenerated and instead showed an empty locule (Fig. 3E). TEM analysis suggested that the abnormal anther development in the TE5A mutant was also primarily due to defects in male mate development during meiosis I.


Aberrant Meiotic Prophase I Leads to Genic Male Sterility in the Novel TE5A Mutant of Brassica napus
TEM micrographs of the anthers from the wild-type (F–J) and the TE5A mutant (A–E). (A,F), early meiotic PMC stage with no detectable differences between the TE5A mutant (A) and the wild type (F); (B,G), the tetrad stage, in the wild type, the PMCs could complete meiosis I and enter the tetrad stage with tetrad formation (G), whereas no dyads or tetrads were observed in the TE5A mutant (B); (C,D,H,I), the microspore stage, microspores were released from the tetrads and covered with an microspore wall in the wild-type (H,I). However, the PMCs of the mutant did not undergo meiosis and developed into pseudo-microspores surrounded by a layer of grains, instead of a typical microspore wall (C,D); (E,J), the pollen grain stage, the wild-type microspores developed into mature pollen grains with the normal exine wall (J), whereas pseudo-microspores of the TE5A mutant were degenerated, resulting in an empty locule. T, tapetum; PMC, pollen mother cell; Tds, tetrad; Msp, microspore; Psm, pseudo-microspore; Dps, degenerating pseudo-microspore; PG: pollen grain; Scale bars = 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037387&req=5

f3: TEM micrographs of the anthers from the wild-type (F–J) and the TE5A mutant (A–E). (A,F), early meiotic PMC stage with no detectable differences between the TE5A mutant (A) and the wild type (F); (B,G), the tetrad stage, in the wild type, the PMCs could complete meiosis I and enter the tetrad stage with tetrad formation (G), whereas no dyads or tetrads were observed in the TE5A mutant (B); (C,D,H,I), the microspore stage, microspores were released from the tetrads and covered with an microspore wall in the wild-type (H,I). However, the PMCs of the mutant did not undergo meiosis and developed into pseudo-microspores surrounded by a layer of grains, instead of a typical microspore wall (C,D); (E,J), the pollen grain stage, the wild-type microspores developed into mature pollen grains with the normal exine wall (J), whereas pseudo-microspores of the TE5A mutant were degenerated, resulting in an empty locule. T, tapetum; PMC, pollen mother cell; Tds, tetrad; Msp, microspore; Psm, pseudo-microspore; Dps, degenerating pseudo-microspore; PG: pollen grain; Scale bars = 10 μm.
Mentions: Analysis of paraffin-cross sections of anther sections had indicated that the early detectable defect in the TE5A mutant involved the disruption of meiosis I, which then led to a failure in dyad or tetrad generation in the anther. To further understand the abnormalities in the mutant, TEM was used to compare the differences in anther development between the mutant and wild-type plants. First, tapetal development during meiosis was normal in the TE5A mutant compared to that in the wild-type (Fig. 3). For male mate development, similar to the observations using paraffin-cross sections, no detectable differences in the early PMC stage were observed between the TE5A mutant and the wild-type (Fig. 3A,F). However, some differences in male mate development after the early PMC stage were observed between the mutant and the wild-type. In the wild-type, the PMCs completed meiosis I and entered the tetrad stage (Fig. 3G). However, at this stage, no dyads or tetrads were observed in the TE5A mutant, and only PMCs were observed (Fig. 3B). Subsequently, the wild-type microspores were released from the tetrads and were covered with a microspore wall (Fig. 3H,I), and in contrast to that observed in the wild-type, the PMCs of the mutant did not accomplish meiosis I and developed into pseudo-microspores that were surrounded by a layer of grains, instead of the a typical microspore wall (Fig. 3C,D). Finally, the wild-type microspores underwent mitosis and developed into mature pollen grains with the normal exine wall (Fig. 3J), whereas the pseudo-microspores of the TE5A mutant degenerated and instead showed an empty locule (Fig. 3E). TEM analysis suggested that the abnormal anther development in the TE5A mutant was also primarily due to defects in male mate development during meiosis I.

View Article: PubMed Central - PubMed

ABSTRACT

Genic male sterility (GMS) has already been extensively utilized for hybrid rapeseed production. TE5A is a novel thermo-sensitive dominant GMS line in Brassica napus, however, its mechanisms of GMS remain largely unclear. Histological and Transmission electron microscopy (TEM) analyses of anthers showed that the male gamete development of TE5A was arrested at meiosis prophase I. EdU uptake of S-phase meiocytes revealed that the TE5A mutant could accomplish DNA replication, however, chromosomal and fluorescence in situ hybridization (FISH) analyses of TE5A showed that homologous chromosomes could not pair, synapse, condense and form bivalents. We then analyzed the transcriptome differences between young floral buds of sterile plants and its near-isogenic fertile plants through RNA-Seq. A total of 3,841 differentially expressed genes (DEGs) were obtained, some of which were associated with homologous chromosome behavior and cell cycle control during meiosis. Dynamic expression changes of selected candidate DEGs were then analyzed at different anther developmental stages. The present study not only demonstrated that the TE5A mutant had defects in meiotic prophase I via detailed cytological analysis, but also provided a global insight into GMS-associated DEGs and elucidated the mechanisms of GMS in TE5A through RNA-Seq.

No MeSH data available.


Related in: MedlinePlus