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LACHESIS restricts gametic cell fate in the female gametophyte of Arabidopsis.

Gross-Hardt R, Kägi C, Baumann N, Moore JM, Baskar R, Gagliano WB, Jürgens G, Grossniklaus U - PLoS Biol. (2007)

Bottom Line: In lis mutants, accessory cells differentiate gametic cell fate, indicating that LIS is involved in a mechanism that prevents accessory cells from adopting gametic cell fate.The temporal and spatial pattern of LIS expression suggests that this mechanism is generated in gametic cells.LIS is homologous to the yeast splicing factor PRP4, indicating that components of the splice apparatus participate in cell fate decisions.

View Article: PubMed Central - PubMed

Affiliation: Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland. rita.gross-hardt@zmbp.uni-tuebingen.de

ABSTRACT
In flowering plants, the egg and sperm cells form within haploid gametophytes. The female gametophyte of Arabidopsis consists of two gametic cells, the egg cell and the central cell, which are flanked by five accessory cells. Both gametic and accessory cells are vital for fertilization; however, the mechanisms that underlie the formation of accessory versus gametic cell fate are unknown. In a screen for regulators of egg cell fate, we isolated the lachesis (lis) mutant which forms supernumerary egg cells. In lis mutants, accessory cells differentiate gametic cell fate, indicating that LIS is involved in a mechanism that prevents accessory cells from adopting gametic cell fate. The temporal and spatial pattern of LIS expression suggests that this mechanism is generated in gametic cells. LIS is homologous to the yeast splicing factor PRP4, indicating that components of the splice apparatus participate in cell fate decisions.

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Functional Analysis of Synergids and Central Cells in lis-1/LIS Plants(A–C) GUS staining in synergids after fertilization of wild-type and lis-1/LIS plants with pollen from the ET434G pollen-tube marker line. (A) Ovule with GUS-stained synergids. The arrowhead points at pollen tube. (B) Ovule in which no GUS staining was detected in synergids. (C) Frequencies of GUS negative synergids. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 50.8%, n = 789; wild-type: 21.5%, n = 287).(D–F) Endosperm development after fertilization of wild-type and lis-1/LIS plants with wild-type pollen. (D) Ovule with developing embryo (star) and endosperm (arrowhead). (E) Ovule with a developing embryo (star), but no endosperm. The undeveloped central cell nucleus is visible (arrowhead). (F) Frequencies of ovules with a developing embryo, but no endosperm. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 11.2%, n = 267; wild type: 0.5%, n = 191).
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pbio-0050047-g003: Functional Analysis of Synergids and Central Cells in lis-1/LIS Plants(A–C) GUS staining in synergids after fertilization of wild-type and lis-1/LIS plants with pollen from the ET434G pollen-tube marker line. (A) Ovule with GUS-stained synergids. The arrowhead points at pollen tube. (B) Ovule in which no GUS staining was detected in synergids. (C) Frequencies of GUS negative synergids. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 50.8%, n = 789; wild-type: 21.5%, n = 287).(D–F) Endosperm development after fertilization of wild-type and lis-1/LIS plants with wild-type pollen. (D) Ovule with developing embryo (star) and endosperm (arrowhead). (E) Ovule with a developing embryo (star), but no endosperm. The undeveloped central cell nucleus is visible (arrowhead). (F) Frequencies of ovules with a developing embryo, but no endosperm. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 11.2%, n = 267; wild type: 0.5%, n = 191).

Mentions: To determine whether lis-1 female gametophytes are indeed defective in cell specification, we examined morphological, molecular, and functional characteristics of the different cell types in lis-1 gametophytes (Figures 1, 2, and 3, respectively). Until cellularization, gametophytes were indistinguishable between lis-1/LIS and wild-type plants (unpublished data), indicating that LIS is not required for any previous step, including mitotic divisions, migration of nuclei, or cellularization. The first defects in lis-1 female gametophytes were consistently observed only after cellularization, corresponding to the wild-type stage at which the different cell types establish distinct morphological and molecular characteristics, as described below. Wild-type synergids differ morphologically from egg cells by two features. First, the synergid nuclei are smaller than the egg cell nucleus. Second, the polarity of synergids is reversed with respect to nuclear position [11,12] (Figure 1G). In lis-1/LIS plants, however, synergids differentiated the morphological attributes of egg cell fate and were often indistinguishable from egg cells (Figure 1J; Table 1). Additionally, the expression of the synergid marker ET2634 was down-regulated in many lis-1 gametophytes (Figure 2D–2F). To test whether the pollen tube–attracting activity of synergids was affected as well, we pollinated lis-1/LIS and wild-type plants with a marker line expressing GUS in the pollen tube (ET434G) (Figure 3A). The number of ovules without GUS staining was strongly increased in lis-1/LIS plants as compared to wild type (Figure 3A–3C), implying that pollen tube attraction was compromised in the majority of lis-1 mutant female gametophytes. These data, together with the ectopic expression of the egg cell marker in the synergids, indicate that lis-1 mutant synergids differentiate egg cell attributes at the expense of synergid cell fate. A different synergid marker (ET884) was ectopically expressed in lis-1 gametophytes (Figure 2G–2I). This intriguing expression shows that not all aspects of accessory and gametic cell fate are mutually exclusive. However, the reduced pollen tube attraction in lis-1 indicates that this marker is unlikely to reflect fully differentiated synergid cell fate.


LACHESIS restricts gametic cell fate in the female gametophyte of Arabidopsis.

Gross-Hardt R, Kägi C, Baumann N, Moore JM, Baskar R, Gagliano WB, Jürgens G, Grossniklaus U - PLoS Biol. (2007)

Functional Analysis of Synergids and Central Cells in lis-1/LIS Plants(A–C) GUS staining in synergids after fertilization of wild-type and lis-1/LIS plants with pollen from the ET434G pollen-tube marker line. (A) Ovule with GUS-stained synergids. The arrowhead points at pollen tube. (B) Ovule in which no GUS staining was detected in synergids. (C) Frequencies of GUS negative synergids. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 50.8%, n = 789; wild-type: 21.5%, n = 287).(D–F) Endosperm development after fertilization of wild-type and lis-1/LIS plants with wild-type pollen. (D) Ovule with developing embryo (star) and endosperm (arrowhead). (E) Ovule with a developing embryo (star), but no endosperm. The undeveloped central cell nucleus is visible (arrowhead). (F) Frequencies of ovules with a developing embryo, but no endosperm. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 11.2%, n = 267; wild type: 0.5%, n = 191).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1804285&req=5

pbio-0050047-g003: Functional Analysis of Synergids and Central Cells in lis-1/LIS Plants(A–C) GUS staining in synergids after fertilization of wild-type and lis-1/LIS plants with pollen from the ET434G pollen-tube marker line. (A) Ovule with GUS-stained synergids. The arrowhead points at pollen tube. (B) Ovule in which no GUS staining was detected in synergids. (C) Frequencies of GUS negative synergids. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 50.8%, n = 789; wild-type: 21.5%, n = 287).(D–F) Endosperm development after fertilization of wild-type and lis-1/LIS plants with wild-type pollen. (D) Ovule with developing embryo (star) and endosperm (arrowhead). (E) Ovule with a developing embryo (star), but no endosperm. The undeveloped central cell nucleus is visible (arrowhead). (F) Frequencies of ovules with a developing embryo, but no endosperm. Dark bars represent wild-type, light bars represent lis-1/LIS plants. The y-axis shows the percentage of the scored phenotype (lis-1/LIS: 11.2%, n = 267; wild type: 0.5%, n = 191).
Mentions: To determine whether lis-1 female gametophytes are indeed defective in cell specification, we examined morphological, molecular, and functional characteristics of the different cell types in lis-1 gametophytes (Figures 1, 2, and 3, respectively). Until cellularization, gametophytes were indistinguishable between lis-1/LIS and wild-type plants (unpublished data), indicating that LIS is not required for any previous step, including mitotic divisions, migration of nuclei, or cellularization. The first defects in lis-1 female gametophytes were consistently observed only after cellularization, corresponding to the wild-type stage at which the different cell types establish distinct morphological and molecular characteristics, as described below. Wild-type synergids differ morphologically from egg cells by two features. First, the synergid nuclei are smaller than the egg cell nucleus. Second, the polarity of synergids is reversed with respect to nuclear position [11,12] (Figure 1G). In lis-1/LIS plants, however, synergids differentiated the morphological attributes of egg cell fate and were often indistinguishable from egg cells (Figure 1J; Table 1). Additionally, the expression of the synergid marker ET2634 was down-regulated in many lis-1 gametophytes (Figure 2D–2F). To test whether the pollen tube–attracting activity of synergids was affected as well, we pollinated lis-1/LIS and wild-type plants with a marker line expressing GUS in the pollen tube (ET434G) (Figure 3A). The number of ovules without GUS staining was strongly increased in lis-1/LIS plants as compared to wild type (Figure 3A–3C), implying that pollen tube attraction was compromised in the majority of lis-1 mutant female gametophytes. These data, together with the ectopic expression of the egg cell marker in the synergids, indicate that lis-1 mutant synergids differentiate egg cell attributes at the expense of synergid cell fate. A different synergid marker (ET884) was ectopically expressed in lis-1 gametophytes (Figure 2G–2I). This intriguing expression shows that not all aspects of accessory and gametic cell fate are mutually exclusive. However, the reduced pollen tube attraction in lis-1 indicates that this marker is unlikely to reflect fully differentiated synergid cell fate.

Bottom Line: In lis mutants, accessory cells differentiate gametic cell fate, indicating that LIS is involved in a mechanism that prevents accessory cells from adopting gametic cell fate.The temporal and spatial pattern of LIS expression suggests that this mechanism is generated in gametic cells.LIS is homologous to the yeast splicing factor PRP4, indicating that components of the splice apparatus participate in cell fate decisions.

View Article: PubMed Central - PubMed

Affiliation: Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland. rita.gross-hardt@zmbp.uni-tuebingen.de

ABSTRACT
In flowering plants, the egg and sperm cells form within haploid gametophytes. The female gametophyte of Arabidopsis consists of two gametic cells, the egg cell and the central cell, which are flanked by five accessory cells. Both gametic and accessory cells are vital for fertilization; however, the mechanisms that underlie the formation of accessory versus gametic cell fate are unknown. In a screen for regulators of egg cell fate, we isolated the lachesis (lis) mutant which forms supernumerary egg cells. In lis mutants, accessory cells differentiate gametic cell fate, indicating that LIS is involved in a mechanism that prevents accessory cells from adopting gametic cell fate. The temporal and spatial pattern of LIS expression suggests that this mechanism is generated in gametic cells. LIS is homologous to the yeast splicing factor PRP4, indicating that components of the splice apparatus participate in cell fate decisions.

Show MeSH