Partially redundant functions of two SET-domain polycomb-group proteins in controlling initiation of seed development in Arabidopsis - PubMed (original) (raw)

Partially redundant functions of two SET-domain polycomb-group proteins in controlling initiation of seed development in Arabidopsis

Dongfang Wang et al. Proc Natl Acad Sci U S A. 2006.

Abstract

In Arabidopsis, a complex of Polycomb-group (PcG) proteins functions in the female gametophyte to control the initiation of seed development. Mutations in the PcG genes, including MEDEA (MEA) and FERTILIZATION-INDEPENDENT SEED 2 (FIS2), produce autonomous seeds where endosperm proliferation occurs in the absence of fertilization. By using a yeast two-hybrid screen, we identified MEA and a related protein, SWINGER (SWN), as SET-domain partners of FIS2. Localization data indicated that all three proteins are present in the female gametophyte. Although single-mutant swn plants did not show any defects, swn mutations enhanced the mea mutant phenotype in producing autonomous seeds. Thus, MEA and SWN perform partially redundant functions in controlling the initiation of endosperm development before fertilization in Arabidopsis.

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Conflict of interest statement

Conflict of interest statement: No conflicts declared.

Figures

Fig. 1.

Fig. 1.

Interaction of FIS2 with SET-domain PcG proteins in yeast and in vitro. (A) Mapping MEA-interacting domains of FIS2 by using Y2H assays. The deletion constructs of FIS2 are shown schematically with numbers indicating the position of amino acids included in each construct. Diploid yeast harboring both pGBK (BD) and pGAD (AD) constructs were spotted on QDO (synthetic complete medium minus leucine, tryptophan, adenine, and histidine) and DDO (synthetic complete medium minus leucine and tryptophan). (B) Interaction of FIS2 and FIE with three SET-domain PcG proteins using Y2H assays is indicated by the growth of yeast on QDO medium. empty, empty pGBK, or pGAD vector. (C) In vitro binding of myc-tagged FIS2 (641–813) polypeptide with HA-tagged full-length MEA, SWN, and FIE labeled with [35S]methionine. The input lane (i) corresponds to 5% of the protein used for in vitro coimmunoprecipitation assays in output lanes (o).

Fig. 2.

Fig. 2.

Expression of SWN-GFP, FIS2-YFP, and MEA-YFP during FG and early seed development. (I–X) Schematic representations of stages of FG and early endosperm development in Arabidopsis. The FG is formed from a surviving megaspore after the megaspore mother cell undergoes meiosis (I). The shaded areas in II–VI represent the developing FGs (26). Dividing endosperm nuclei during early seed development are depicted in VII–X. (A–T) Epifluorescence images of GFP/YFP activity corresponding to stages shown in I–V (A–E) and VI–X (F–J, K–O, and P–T). Images were obtained with the focal planes through the megaspore mother cell (A), developing FG (B–F, K, and P), or developing endosperm (G–J, L–O, and Q–T). (A–J) SWN-GFP expression. In most transgenic plants, SWN-GFP expression was not detectable in the endosperm (G–H). (K–O) FIS2-YFP expression. (P–T) MEA-YFP expression. an, antipodal cell nucleus; cn, chalazal nucleus; ccn, central cell nucleus; dsn, degenerating synergid nucleus; ecn, egg cell nucleus; en, endosperm nucleus; fmn, functional megaspore nucleus; mn, micropylar nucleus; ncd, nuclear cytoplasmic domain; pn, polar nucleus; sn, synergid cell nucleus; zn, zygote nucleus. [Scale bars: 10 μm (A–E); 30 μm (F–T).]

Fig. 3.

Fig. 3.

Expression of SWN-GFP in ovule, seed, and vegetative structures. (A) Bright-field (Left) and the corresponding epifluorescence (Right) images of a flower stage 13 (44) ovule showing SWN-GFP in all nuclei of the integument cells. The focal plane is through the outer integument. (B) Epifluorescence image of a developing seed containing a heart-stage embryo. (C) Epifluorescence image of a bent cotyledon-stage embryo dissected away from the endosperm and seed coat. (D) Bright-field (Upper) and the corresponding epifluorescence (Lower) images of a trichome on the surface of a rosette leaf. (E) Bright-field (Upper) and the corresponding epifluorescence (Lower) images of a root tip. (F) Bright-field (Upper) and the corresponding epifluorescence (Lower) images of a lateral root primordium and a lateral root. he, heart stage embryo; lrp, lateral root primordium; tn, trichome cell nucleus. (Scale bars: 30 μm.)

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