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Correlation between a loss of auxin signaling and a loss of proliferation in maize antipodal cells.

Chettoor AM, Evans MM - Front Plant Sci (2015)

Bottom Line: In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells.Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells.The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Carnegie Institution for Science Stanford, CA USA.

ABSTRACT
The plant life cycle alternates between two genetically active generations: the diploid sporophyte and the haploid gametophyte. In angiosperms the gametophytes are sexually dimorphic and consist of only a few cells. The female gametophyte, or embryo sac, is comprised of four cell types: two synergids, an egg cell, a central cell, and a variable number of antipodal cells. In some species the antipodal cells are indistinct and fail to proliferate, so many aspects of antipodal cell function and development have been unclear. In maize and many other grasses, the antipodal cells proliferate to produce a highly distinct cluster at the chalazal end of the embryo sac that persists at the apex of the endosperm after fertilization. The antipodal cells are a site of auxin accumulation in the maize embryo sac. Analysis of different families of genes involved in auxin biosynthesis, distribution, and signaling for expression in the embryo sac demonstrates that all steps are expressed within the embryo sac. In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells. Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells. The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

No MeSH data available.


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Effect of Lxm1-O on embryo sac expression of pPIN1::PIN1-YFP and pDR5::RFP. Live cell imaging of sibling (A,C) wild-type and (B,D)Lxm1-O embryo sacs from Lxm1-O heterozygotes segregating either (A,B)pPIN1::PIN1-YFP or (C,D)pDR5::RFP. (A) Embryo sac expressing pPIN1::PIN1-YFP. (C) Embryo sac expressing pDR5::RFP. The small antipodal cell cluster distinguishes Lxm1-O from wild-type. Neither DR5 nor PIN1 are expressed in mutant Lxm1-O embryo sacs. Arrows indicate antipodal cell cluster. Arrowheads indicate DR5 expression in the micropylar nucellus. Scale bar = 100 μm. (E) Embryo sacs were visualized at three different sensitivity settings for DR5 expression: a gain of 940, 1100, or 1250. This was used as a proxy for relative DR5 expression between embryo sacs. For most of the normal embryo sacs, DR5 expression could first be detected at the lower gain settings used, while for most of the mutant embryo sacs DR5 expression either was not detected at all or was only detected at the highest setting.
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Figure 7: Effect of Lxm1-O on embryo sac expression of pPIN1::PIN1-YFP and pDR5::RFP. Live cell imaging of sibling (A,C) wild-type and (B,D)Lxm1-O embryo sacs from Lxm1-O heterozygotes segregating either (A,B)pPIN1::PIN1-YFP or (C,D)pDR5::RFP. (A) Embryo sac expressing pPIN1::PIN1-YFP. (C) Embryo sac expressing pDR5::RFP. The small antipodal cell cluster distinguishes Lxm1-O from wild-type. Neither DR5 nor PIN1 are expressed in mutant Lxm1-O embryo sacs. Arrows indicate antipodal cell cluster. Arrowheads indicate DR5 expression in the micropylar nucellus. Scale bar = 100 μm. (E) Embryo sacs were visualized at three different sensitivity settings for DR5 expression: a gain of 940, 1100, or 1250. This was used as a proxy for relative DR5 expression between embryo sacs. For most of the normal embryo sacs, DR5 expression could first be detected at the lower gain settings used, while for most of the mutant embryo sacs DR5 expression either was not detected at all or was only detected at the highest setting.

Mentions: To test whether Lxm1-O affects auxin distribution in the embryo sac, pPIN1a::PIN1a-YFP and pDR5::RFP were crossed with Lxm1-O/+ mutant lines. Plants heterozygous for Lxm1-O and hemizygous for either pPIN1a::PIN1a-YFP or pDR5::RFP were examined for effects of Lxm1-O on auxin signaling in the embryo sac. Examination of mutant plants revealed that the Lxm1-O mutation interferes with expression of both PIN1a and DR5 in maize antipodal cells (Figure 7 and Table 3). In plants heterozygous for Lxm1-O and hemizygous for pPIN1a::PIN1a-YFP, approximately half of the normal embryo sacs express the transgene, as expected, but none of the abnormal embryo sacs express the transgene. The effect of Lxm1-O on pDR5::RFP expression is essentially the same as for pPIN1a::PIN1a-YFP, with only 1 of 17 abnormal embryo sacs expressing the transgene, with the one exceptional individual having an intermediate antipodal cell phenotype. For pDR5::RFP fewer than half of the wild type embryo sacs express the transgene, perhaps reflecting silencing of this construct, but still a significantly higher frequency of normal embryo sacs than mutant embryo sacs are positive for DR5.


Correlation between a loss of auxin signaling and a loss of proliferation in maize antipodal cells.

Chettoor AM, Evans MM - Front Plant Sci (2015)

Effect of Lxm1-O on embryo sac expression of pPIN1::PIN1-YFP and pDR5::RFP. Live cell imaging of sibling (A,C) wild-type and (B,D)Lxm1-O embryo sacs from Lxm1-O heterozygotes segregating either (A,B)pPIN1::PIN1-YFP or (C,D)pDR5::RFP. (A) Embryo sac expressing pPIN1::PIN1-YFP. (C) Embryo sac expressing pDR5::RFP. The small antipodal cell cluster distinguishes Lxm1-O from wild-type. Neither DR5 nor PIN1 are expressed in mutant Lxm1-O embryo sacs. Arrows indicate antipodal cell cluster. Arrowheads indicate DR5 expression in the micropylar nucellus. Scale bar = 100 μm. (E) Embryo sacs were visualized at three different sensitivity settings for DR5 expression: a gain of 940, 1100, or 1250. This was used as a proxy for relative DR5 expression between embryo sacs. For most of the normal embryo sacs, DR5 expression could first be detected at the lower gain settings used, while for most of the mutant embryo sacs DR5 expression either was not detected at all or was only detected at the highest setting.
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Figure 7: Effect of Lxm1-O on embryo sac expression of pPIN1::PIN1-YFP and pDR5::RFP. Live cell imaging of sibling (A,C) wild-type and (B,D)Lxm1-O embryo sacs from Lxm1-O heterozygotes segregating either (A,B)pPIN1::PIN1-YFP or (C,D)pDR5::RFP. (A) Embryo sac expressing pPIN1::PIN1-YFP. (C) Embryo sac expressing pDR5::RFP. The small antipodal cell cluster distinguishes Lxm1-O from wild-type. Neither DR5 nor PIN1 are expressed in mutant Lxm1-O embryo sacs. Arrows indicate antipodal cell cluster. Arrowheads indicate DR5 expression in the micropylar nucellus. Scale bar = 100 μm. (E) Embryo sacs were visualized at three different sensitivity settings for DR5 expression: a gain of 940, 1100, or 1250. This was used as a proxy for relative DR5 expression between embryo sacs. For most of the normal embryo sacs, DR5 expression could first be detected at the lower gain settings used, while for most of the mutant embryo sacs DR5 expression either was not detected at all or was only detected at the highest setting.
Mentions: To test whether Lxm1-O affects auxin distribution in the embryo sac, pPIN1a::PIN1a-YFP and pDR5::RFP were crossed with Lxm1-O/+ mutant lines. Plants heterozygous for Lxm1-O and hemizygous for either pPIN1a::PIN1a-YFP or pDR5::RFP were examined for effects of Lxm1-O on auxin signaling in the embryo sac. Examination of mutant plants revealed that the Lxm1-O mutation interferes with expression of both PIN1a and DR5 in maize antipodal cells (Figure 7 and Table 3). In plants heterozygous for Lxm1-O and hemizygous for pPIN1a::PIN1a-YFP, approximately half of the normal embryo sacs express the transgene, as expected, but none of the abnormal embryo sacs express the transgene. The effect of Lxm1-O on pDR5::RFP expression is essentially the same as for pPIN1a::PIN1a-YFP, with only 1 of 17 abnormal embryo sacs expressing the transgene, with the one exceptional individual having an intermediate antipodal cell phenotype. For pDR5::RFP fewer than half of the wild type embryo sacs express the transgene, perhaps reflecting silencing of this construct, but still a significantly higher frequency of normal embryo sacs than mutant embryo sacs are positive for DR5.

Bottom Line: In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells.Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells.The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Carnegie Institution for Science Stanford, CA USA.

ABSTRACT
The plant life cycle alternates between two genetically active generations: the diploid sporophyte and the haploid gametophyte. In angiosperms the gametophytes are sexually dimorphic and consist of only a few cells. The female gametophyte, or embryo sac, is comprised of four cell types: two synergids, an egg cell, a central cell, and a variable number of antipodal cells. In some species the antipodal cells are indistinct and fail to proliferate, so many aspects of antipodal cell function and development have been unclear. In maize and many other grasses, the antipodal cells proliferate to produce a highly distinct cluster at the chalazal end of the embryo sac that persists at the apex of the endosperm after fertilization. The antipodal cells are a site of auxin accumulation in the maize embryo sac. Analysis of different families of genes involved in auxin biosynthesis, distribution, and signaling for expression in the embryo sac demonstrates that all steps are expressed within the embryo sac. In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells. Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells. The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

No MeSH data available.


Related in: MedlinePlus