Limits...
Loss-of-function mutants and overexpression lines of the Arabidopsis cyclin CYCA1;2/Tardy Asynchronous Meiosis exhibit different defects in prophase-i meiocytes but produce the same meiotic products.

Wang Y, Yang M - PLoS ONE (2014)

Bottom Line: We also found that the pericentromeric heterochromatin regions in male meiocytes in tam-1 and tam-2 (a allele) frequently formed a tight cluster at the pachytene and diplotene stages, in contrast to the infrequent occurrences of such clusters in the wild type and the ASK1:TAM line.The level of ASY1, however, was greatly reduced in another ASK1:TAM line with much overexpressed TAM.Our results indicate that the reduction and increase in the activity of TAM differentially affect chromosomal morphology and the action of ASY1 in prophase I.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany, Oklahoma State University, Stillwater, Oklahoma, United States of America.

ABSTRACT
In Arabidopsis, loss-of-function mutations in the A-type cyclin CYCA1;2/Tardy Asynchronous Meiosis (TAM) gene lead to the production of abnormal meiotic products including triads and dyads. Here we report that overexpression of TAM by the ASK1:TAM transgene also led to the production of triads and dyads in meiosis, as well as shriveled seeds, in a dominant fashion. However, the partial loss-of-function mutant tam-1, an ASK1:TAM line, and the wild type differed in dynamic changes in chromosome thread thickness from zygotene to diplotene. We also found that the pericentromeric heterochromatin regions in male meiocytes in tam-1 and tam-2 (a allele) frequently formed a tight cluster at the pachytene and diplotene stages, in contrast to the infrequent occurrences of such clusters in the wild type and the ASK1:TAM line. Immunolocalization studies of the chromosome axial component ASY1 revealed that ASY1 was highly expressed at the appropriate male meiotic stages but not localized to the chromosomes in tam-2. The level of ASY1, however, was greatly reduced in another ASK1:TAM line with much overexpressed TAM. Our results indicate that the reduction and increase in the activity of TAM differentially affect chromosomal morphology and the action of ASY1 in prophase I. Based on these results, we propose that either the different meiotic defects or a common defect such as missing ASY1 on the chromosomal axes triggers a hitherto uncharacterized cell cycle checkpoint in the male meiocytes in the tam mutants and ASK1:TAM lines, leading to the production of the same abnormal meiotic products.

No MeSH data available.


Related in: MedlinePlus

Male meiotic products in the wild type (Col) and T1 of ASK1:TAM2.(A) Normal tetrads in Col. (B–D) A dyad, a triad, and a tetrad in ASK1:TAM2, respectively. Bar = 25 µm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4234643&req=5

pone-0113348-g001: Male meiotic products in the wild type (Col) and T1 of ASK1:TAM2.(A) Normal tetrads in Col. (B–D) A dyad, a triad, and a tetrad in ASK1:TAM2, respectively. Bar = 25 µm.

Mentions: It was previously reported that overexpression of TAM by the ASK1 promoter led to the production of polyploid plants [19]. To investigate the cellular basis for such an effect, a total of 36 T1 plants were obtained from six independent transformation experiments that introduced the ASK1:TAM transgene into the wild-type plants. Male meiotic products in these plants were then examined. As indicated in Table 1 and Fig. 1, 30 T1 plants from four of the transformation experiments produced either apparently normal tetrads or abnormal products such as dyads or a mixture of dyads, triads, and tetrads. Four T1 plants from one remaining transformation experiment produced only tetrads while two plants from still another transformation experiment produced only dyads or a mixture of dyads, triads, and tetrads. The abnormal meiotic products should also have occurred in female meiosis in some of these lines because progeny from at least one of the lines, ASK1:TAM1, were tetraploid [19]. Furthermore, 34 of these plants produced variable amounts of dark and collapsed seeds (Fig. 2). The number of lines producing the abnormal seeds is much larger than that of the lines producing the abnormal meiotic products, indicating that the seed defect is independent of the production of abnormal meiotic products, and that seed development is more sensitive to the overexpression of TAM than meiotic cell cycle progression. The variation in the severity of these defects likely resulted from the variation in the expression level of the transgene in these plants [19]. Because heterozygosity for the transgene is expected in T1 plants, the presence of these abnormalities in the T1 plants indicates that the transgene had a dominate effect on meiosis and seed development.


Loss-of-function mutants and overexpression lines of the Arabidopsis cyclin CYCA1;2/Tardy Asynchronous Meiosis exhibit different defects in prophase-i meiocytes but produce the same meiotic products.

Wang Y, Yang M - PLoS ONE (2014)

Male meiotic products in the wild type (Col) and T1 of ASK1:TAM2.(A) Normal tetrads in Col. (B–D) A dyad, a triad, and a tetrad in ASK1:TAM2, respectively. Bar = 25 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4234643&req=5

pone-0113348-g001: Male meiotic products in the wild type (Col) and T1 of ASK1:TAM2.(A) Normal tetrads in Col. (B–D) A dyad, a triad, and a tetrad in ASK1:TAM2, respectively. Bar = 25 µm.
Mentions: It was previously reported that overexpression of TAM by the ASK1 promoter led to the production of polyploid plants [19]. To investigate the cellular basis for such an effect, a total of 36 T1 plants were obtained from six independent transformation experiments that introduced the ASK1:TAM transgene into the wild-type plants. Male meiotic products in these plants were then examined. As indicated in Table 1 and Fig. 1, 30 T1 plants from four of the transformation experiments produced either apparently normal tetrads or abnormal products such as dyads or a mixture of dyads, triads, and tetrads. Four T1 plants from one remaining transformation experiment produced only tetrads while two plants from still another transformation experiment produced only dyads or a mixture of dyads, triads, and tetrads. The abnormal meiotic products should also have occurred in female meiosis in some of these lines because progeny from at least one of the lines, ASK1:TAM1, were tetraploid [19]. Furthermore, 34 of these plants produced variable amounts of dark and collapsed seeds (Fig. 2). The number of lines producing the abnormal seeds is much larger than that of the lines producing the abnormal meiotic products, indicating that the seed defect is independent of the production of abnormal meiotic products, and that seed development is more sensitive to the overexpression of TAM than meiotic cell cycle progression. The variation in the severity of these defects likely resulted from the variation in the expression level of the transgene in these plants [19]. Because heterozygosity for the transgene is expected in T1 plants, the presence of these abnormalities in the T1 plants indicates that the transgene had a dominate effect on meiosis and seed development.

Bottom Line: We also found that the pericentromeric heterochromatin regions in male meiocytes in tam-1 and tam-2 (a allele) frequently formed a tight cluster at the pachytene and diplotene stages, in contrast to the infrequent occurrences of such clusters in the wild type and the ASK1:TAM line.The level of ASY1, however, was greatly reduced in another ASK1:TAM line with much overexpressed TAM.Our results indicate that the reduction and increase in the activity of TAM differentially affect chromosomal morphology and the action of ASY1 in prophase I.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany, Oklahoma State University, Stillwater, Oklahoma, United States of America.

ABSTRACT
In Arabidopsis, loss-of-function mutations in the A-type cyclin CYCA1;2/Tardy Asynchronous Meiosis (TAM) gene lead to the production of abnormal meiotic products including triads and dyads. Here we report that overexpression of TAM by the ASK1:TAM transgene also led to the production of triads and dyads in meiosis, as well as shriveled seeds, in a dominant fashion. However, the partial loss-of-function mutant tam-1, an ASK1:TAM line, and the wild type differed in dynamic changes in chromosome thread thickness from zygotene to diplotene. We also found that the pericentromeric heterochromatin regions in male meiocytes in tam-1 and tam-2 (a allele) frequently formed a tight cluster at the pachytene and diplotene stages, in contrast to the infrequent occurrences of such clusters in the wild type and the ASK1:TAM line. Immunolocalization studies of the chromosome axial component ASY1 revealed that ASY1 was highly expressed at the appropriate male meiotic stages but not localized to the chromosomes in tam-2. The level of ASY1, however, was greatly reduced in another ASK1:TAM line with much overexpressed TAM. Our results indicate that the reduction and increase in the activity of TAM differentially affect chromosomal morphology and the action of ASY1 in prophase I. Based on these results, we propose that either the different meiotic defects or a common defect such as missing ASY1 on the chromosomal axes triggers a hitherto uncharacterized cell cycle checkpoint in the male meiocytes in the tam mutants and ASK1:TAM lines, leading to the production of the same abnormal meiotic products.

No MeSH data available.


Related in: MedlinePlus