Limits...
Inefficient double-strand DNA break repair is associated with increased fasciation in Arabidopsis BRCA2 mutants.

Abe K, Osakabe K, Ishikawa Y, Tagiri A, Yamanouchi H, Takyuu T, Yoshioka T, Ito T, Kobayashi M, Shinozaki K, Ichikawa H, Toki S - J. Exp. Bot. (2009)

Bottom Line: An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant.In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation.Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan.

ABSTRACT
BRCA2 is a breast tumour susceptibility factor with functions in maintaining genome stability through ensuring efficient double-strand DNA break (DSB) repair via homologous recombination. Although best known in vertebrates, fungi, and higher plants also possess BRCA2-like genes. To investigate the role of Arabidopsis BRCA2 genes in DNA repair in somatic cells, transposon insertion mutants of the AtBRCA2a and AtBRCA2b genes were identified and characterized. atbrca2a-1 and atbrca2b-1 mutant plants showed hypersensitivity to genotoxic stresses compared to wild-type plants. An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant. In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation. Interestingly, these phenotypes were also induced by gamma-irradiation in wild-type plants. Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression. These data suggest that inefficient DSB repair in the atbrca2a-1/atbrca2b-1 mutant leads to disorganization of the programmed cell cycle of apical meristems.

Show MeSH

Related in: MedlinePlus

Morphological phenotypes of atbrca2 mutants. (A, B) Five-week-old wild-type plants (Nossen), (C, D, E) atbrca2a-1/atbrca2b-1 double mutant plants. (F, G) Cross-sections of stems from 5-week-old plants: wild type (Nossen) (F) and atbrca2a-1/atbrca2b-1 double mutant (G). (H, I) Longitudinal-sections of 2-week-old plants: wild type (Nossen) (H) and atbrca2a-1/atbrca2b-1 double mutant plants (I). (J, K, L) In situ hybridization analysis of the AtWUS gene in wild-type (Nossen) (J) and atbrca2a-1/atbrca2b-1 double mutant (K, L) plants.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2692019&req=5

fig2: Morphological phenotypes of atbrca2 mutants. (A, B) Five-week-old wild-type plants (Nossen), (C, D, E) atbrca2a-1/atbrca2b-1 double mutant plants. (F, G) Cross-sections of stems from 5-week-old plants: wild type (Nossen) (F) and atbrca2a-1/atbrca2b-1 double mutant (G). (H, I) Longitudinal-sections of 2-week-old plants: wild type (Nossen) (H) and atbrca2a-1/atbrca2b-1 double mutant plants (I). (J, K, L) In situ hybridization analysis of the AtWUS gene in wild-type (Nossen) (J) and atbrca2a-1/atbrca2b-1 double mutant (K, L) plants.

Mentions: Both atbrca2a-1 and atbrca2b-1 single mutant and homozygous atbrca2a-1/atbrca2b-1 double mutant plants showed substantially normal vegetative development when compared to wild-type plants (Nossen) (cf. Fig. 2A, C), although abnormal phyllotaxy was occasionally observed (Figs 2B, D, 3). In addition, these mutant plants were fertile. By contrast, Siaud et al. (2004) reported that most plants transformed with an AtBRCA2–RNAi construct under the control of the DMC1 promoter were affected in their fertility (Siaud et al., 2004). Although at first glance this report appears inconsistent with our observations, if our mutants are partially deficient mutants, it is possible for the atbrca2a-1/atbrca2b-1 double mutant to be partially fertile. However, all our atbrca2 single and double mutants were as fertile as the wild type (data not shown). Next, to assess pollen grain viability, anthers were dissected from wild-type (Nossen) and mutant flower buds and stained with Alexander's solution (Alexander, 1969). As shown in Supplementary Table S1 and Fig. S3A at JXB online, more than 95% of wild-type anthers were full of red-coloured, viable pollen grains. On the other hand, although about 80% of double mutant anthers were similar to that of the wild type, about 20% of anthers in double mutant plants contained many green-coloured, non-viable pollen grains (see Supplementary Fig. S3B at JXB online). These results suggested that our atbrca2a-1/atbrca2b-1 double mutant is partially defective in male gamete development, but that this defect does not affect overall fertility.


Inefficient double-strand DNA break repair is associated with increased fasciation in Arabidopsis BRCA2 mutants.

Abe K, Osakabe K, Ishikawa Y, Tagiri A, Yamanouchi H, Takyuu T, Yoshioka T, Ito T, Kobayashi M, Shinozaki K, Ichikawa H, Toki S - J. Exp. Bot. (2009)

Morphological phenotypes of atbrca2 mutants. (A, B) Five-week-old wild-type plants (Nossen), (C, D, E) atbrca2a-1/atbrca2b-1 double mutant plants. (F, G) Cross-sections of stems from 5-week-old plants: wild type (Nossen) (F) and atbrca2a-1/atbrca2b-1 double mutant (G). (H, I) Longitudinal-sections of 2-week-old plants: wild type (Nossen) (H) and atbrca2a-1/atbrca2b-1 double mutant plants (I). (J, K, L) In situ hybridization analysis of the AtWUS gene in wild-type (Nossen) (J) and atbrca2a-1/atbrca2b-1 double mutant (K, L) plants.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2692019&req=5

fig2: Morphological phenotypes of atbrca2 mutants. (A, B) Five-week-old wild-type plants (Nossen), (C, D, E) atbrca2a-1/atbrca2b-1 double mutant plants. (F, G) Cross-sections of stems from 5-week-old plants: wild type (Nossen) (F) and atbrca2a-1/atbrca2b-1 double mutant (G). (H, I) Longitudinal-sections of 2-week-old plants: wild type (Nossen) (H) and atbrca2a-1/atbrca2b-1 double mutant plants (I). (J, K, L) In situ hybridization analysis of the AtWUS gene in wild-type (Nossen) (J) and atbrca2a-1/atbrca2b-1 double mutant (K, L) plants.
Mentions: Both atbrca2a-1 and atbrca2b-1 single mutant and homozygous atbrca2a-1/atbrca2b-1 double mutant plants showed substantially normal vegetative development when compared to wild-type plants (Nossen) (cf. Fig. 2A, C), although abnormal phyllotaxy was occasionally observed (Figs 2B, D, 3). In addition, these mutant plants were fertile. By contrast, Siaud et al. (2004) reported that most plants transformed with an AtBRCA2–RNAi construct under the control of the DMC1 promoter were affected in their fertility (Siaud et al., 2004). Although at first glance this report appears inconsistent with our observations, if our mutants are partially deficient mutants, it is possible for the atbrca2a-1/atbrca2b-1 double mutant to be partially fertile. However, all our atbrca2 single and double mutants were as fertile as the wild type (data not shown). Next, to assess pollen grain viability, anthers were dissected from wild-type (Nossen) and mutant flower buds and stained with Alexander's solution (Alexander, 1969). As shown in Supplementary Table S1 and Fig. S3A at JXB online, more than 95% of wild-type anthers were full of red-coloured, viable pollen grains. On the other hand, although about 80% of double mutant anthers were similar to that of the wild type, about 20% of anthers in double mutant plants contained many green-coloured, non-viable pollen grains (see Supplementary Fig. S3B at JXB online). These results suggested that our atbrca2a-1/atbrca2b-1 double mutant is partially defective in male gamete development, but that this defect does not affect overall fertility.

Bottom Line: An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant.In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation.Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan.

ABSTRACT
BRCA2 is a breast tumour susceptibility factor with functions in maintaining genome stability through ensuring efficient double-strand DNA break (DSB) repair via homologous recombination. Although best known in vertebrates, fungi, and higher plants also possess BRCA2-like genes. To investigate the role of Arabidopsis BRCA2 genes in DNA repair in somatic cells, transposon insertion mutants of the AtBRCA2a and AtBRCA2b genes were identified and characterized. atbrca2a-1 and atbrca2b-1 mutant plants showed hypersensitivity to genotoxic stresses compared to wild-type plants. An atbrca2a-1/atbrca2b-1 double mutant showed an additive increase in sensitivity to genotoxic stresses compared to each single mutant. In addition, it was found that atbrca2 mutant plants displayed fasciation and abnormal phyllotaxy phenotypes with low incidence, and that the ratio of plants exhibiting these phenotypes is increased by gamma-irradiation. Interestingly, these phenotypes were also induced by gamma-irradiation in wild-type plants. Moreover, it was found that shoot apical meristems of the atbrca2a-1/atbrca2b-1 double mutant show altered cell cycle progression. These data suggest that inefficient DSB repair in the atbrca2a-1/atbrca2b-1 mutant leads to disorganization of the programmed cell cycle of apical meristems.

Show MeSH
Related in: MedlinePlus