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First published online October 26, 2007
doi: 10.1242/10.1242/dev.007310

Development 134, 4107-4117 (2007)
Published by The Company of Biologists 2007
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Arabidopsis GLAUCE promotes fertilization-independent endosperm development and expression of paternally inherited alleles

Quy A. Ngo1, James M. Moore2,3, Ramamurthy Baskar2,3, Ueli Grossniklaus2,3 and Venkatesan Sundaresan1,4,*

1 Section of Plant Biology, University of California, One Shields Avenue, Davis, CA 95616, USA.
2 Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.
3 Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland.
4 Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA.


Figure 1
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  		Fig. 1. Normal morphology and intact cell identities of the mature embryo sac in a SET2030 ovule. (A) Mature embryo sac with four cell types: two synergids, one egg cell and one central cell. (B-F) GUS expression of marker lines for specific cell types of glc embryo sacs in mature ovules. Central cell marker lines are FIS2::GUS (B) and MEA::GUS (C), egg cell marker lines are ET1086 (D) and ET1119 (E), and the synergid cell marker line is ET2634 (F). ccn, central cell nucleus; ecn, egg cell nucleus; scn, synergid cell nuclei. Scale bars: 50 µm.

 

Figure 2
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  		Fig. 2. glc (SET2030) phenotypes in fertilized seeds. (A) Wild-type seed at the late globular embryo stage. (B-G) glc seeds without endosperm and with embryos arrested at various stages: one-cell (B), two-cell (C), quadrant (D), octant (E), pre-globular (F), globular (G). (H) glc 16-cell embryo with a cluster of six unequally sized nuclei/nucleoli in the endosperm. (I) High-magnification image of the globular glc embryo in G. (J) Wild-type globular embryo. Arrows indicate the single nucleus/nucleolus or nuclear/nucleolar cluster in the glc central cell. Scale bars: 50 µm.

 

Figure 3
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  		Fig. 3. Ds insertion locus in the glc mutant. (A) CAPS markers in the putative deletion region at the glc locus of the glc(Ler)/GLC(Col) hybrid. L, wild-type Ler; C, wild-type Col; M, glc(Ler)/GLC(Ler); H, F1 hybrid glc(Ler)/GLC(Col); RI, EcoRI. (B) Southern blot of genomic DNA from glc/GLC plant hybridized with the probe within the Ds element represented by the red line in A. M, size marker.

 

Figure 4
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  		Fig. 4. Expression of paternal markers in embryos derived from glc egg cells. Paternal promoter activity of CYCB1;1::GUS (A,B) and PIN7::PIN7-GUS (C,D) in the pre-globular embryos 2.5 DAP of wild-type (wt) seeds (A,C) and of glc seeds (B,D). Scale bars: 50 µm.

 

Figure 5
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  		Fig. 5. DNA content of endosperm nuclei derived from glc central cell. DNA content of the sporophytic integument nuclei (blue bars), the single nucleus (orange or yellow bars) in glc seeds and the endosperm nuclei in wild-type seed (yellow bars). (A,B) glc selfed seeds. (C-F) Out-crossed glc seeds. (G) Wild-type seed. Each graph displays data from one seed. Each seed had its own diploidy reference owing to the laser-scanning settings and variation in dye penetration from seed to seed. As the integument cells of early seeds are simultaneously dividing and expanding (Haughn and Chaudhury, 2005Go), their nuclei have different amounts of DNA depending on where the cells are in the cell cycle. The nuclei with the lowest DNA content represent 2n at G1 (2n=2C), the nuclei with the highest DNA content represent 2n at G2 (2n=4C), and the nuclei with the DNA content between these two values represent the amount of DNA from the mother nucleus plus that from the replicating DNA strands (equivalent to 2C<2n<4C). For each series of 15 sporophytic nuclei of each glc seed, the average of the DNA contents of the three nuclei with the lowest fluorescence intensity was taken as 2C, and of the three nuclei with the highest fluorescence intensity as 4C. The x-axis depicts separate nuclei; the y-axis shows the fluorescence intensity sum of the propidium iodide-stained nuclei. Horizontal dotted lines represent the average 2C level; horizontal dashed lines represent the average 4C level.

 

Figure 6
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  		Fig. 6. PHE1 expression in glc seeds. Embryonic PHE1 expression in wild-type seeds (A,C) and glc seeds (B,D) 2.5-4 DAP from paternal (A,B) and maternal (C,D) PHE1 promoter activity. (A,B) Embryos at the early globular stage. (C,D) Embryos at the pre-globular stage. wt, wild-type. Scale bars: 50 µm.

 

Figure 7
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  		Fig. 7. Expression of paternal markers in glc seeds. Embryonic FAC1 and RPS5a expression in wild-type seeds (A,C) and glc seeds (B,D-F) from the promoter activity of paternal FAC1 (A,B), paternal RPS5a (C-E) and maternal RPS5a (F). (A,B) Embryos at the one-cell stage. (C,D,E) Embryos at the globular stage. (F) Embryo at the eight-cell stage. Arrows in A and B indicate the embryo proper. Arrowhead in B indicates the cell wall of the embryo proper. wt, wild-type. Scale bars: 50 µm.

 

Figure 8
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  		Fig. 8. Proposed GLC functions in the FIS-regulation model for endosperm and embryo development. (A) Before fertilization, GLC promotes fertilization-independent endosperm development in a separate pathway opposing MEA and MSI1. Alternatively, MEA and MSI1 could prevent autonomous endosperm by repressing GLC. (B) After fertilization, maternal GLC directly or indirectly activates bi-parental PHE1, paternal RPS5a and paternal FAC1 to initiate embryo and endosperm proliferation independently of MEA-FIE or as a downstream repression target of MEA-FIE. Maternal MEA-FIE checks and balances this cellular proliferation by repressing maternal PHE1, MEIDOS and possibly maternal GLC.

 

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© The Company of Biologists Ltd 2007