Ovule Development in Wild-Type Arabidopsis and Two Female-Sterile Mutants.

Abstract

Ovules are complex structures that are present in all seed bearing plants and are contained within the carpels in flowering plants. Ovules are the site of megasporogenesis and megagametogenesis and, following fertilization, develop into seeds. We combined genetic methods with anatomical and morphological analyses to dissect ovule development. Here, we present a detailed description of the morphological development of Arabidopsis ovules and report on the isolation of two chemically induced mutants, bell (bell) and short integuments (sinl), with altered ovule development. Phenotypic analyses indicated that bell mutants initiate a single integument-like structure that develops aberrantly. sinl mutants initiate two integuments, but growth of the integuments is disrupted such that cell division continues without normal cell elongation. Both mutants can differentiate archesporial cells, but neither forms a normal embryo sac. Genetic analyses indicated that bell segregates as a single recessive mutation, and complementation tests showed that the two mutants are not allelic. The phenotypes of the mutants indicate that normal morphological development of the integuments and proper embryo sac formation are interdependent or are governed in part by common pathways. The ovule mutants that we describe in Arabidopsis represent nove1 genetic tools for the study of this stage of reproductive development.

Development of a luciferase-based reporter of transcriptional gene silencing that enables bidirectional mutant screening in Arabidopsis thaliana

“…Arabidopsis mutants used in this study were rdr6–11 [11], dcl1–7 [18], se-1 [19], hyl1 [20], met1–3 [21], cmt3–7 [17] and drd3–1 [22] and newly isolated drm2–6 , ago4–6 , drd1–12 , hen1–9 , ros1–5 and mom1–5 . For map-based cloning of newly isolated mutants, LUCH rdr6–11 in the Columbia-0 (Col-0) accession was introgressed into Landsberg erecta (L er ) by backcrossing to L er five times and one line with a similar level of LUC activity as LUCH in Col-0 was isolated.…”

Arabidopsis PRC1 core component AtRING1 regulates stem cell-determining carpel development mainly through repression of class I KNOX genes

“…In normal WT ovule development, prior to anthesis the nucellus degenerates, leaving the ES in direct contact with the endothelium (integumentary tapetum), differentiated from the inner layer of the inner integument (FG1 and FG2-I, Fig. 4a; [35, 36]). In contrast, most atring1a;atring1b mutant ovules display an overproliferated nucellus growing out of outer and inner integuments (Fig.…”

“…Many gametophytic ovule mutants have normal sporophytic tissue structures, but sporophytic ovule mutants usually have abnormal gametophyte development, suggesting that integument and ES development are interdependent processes and that accurate architecture of sporophytic tissue is necessary for successful development of a fully functional gametophyte [52]. For example, bell1 ( bel1 ) ovules develop a single integument-like structure (ILS) taking the place of the two integuments, and fail to produce a normal ES [36, 53, 54]. In short integuments1 ( sin1 ) ovules, both integuments are too short to enclose the nucellus, and the ES does not develop [36, 55].…”

“…For example, bell1 ( bel1 ) ovules develop a single integument-like structure (ILS) taking the place of the two integuments, and fail to produce a normal ES [36, 53, 54]. In short integuments1 ( sin1 ) ovules, both integuments are too short to enclose the nucellus, and the ES does not develop [36, 55]. Therefore, continuous signaling from sporophytic tissue appears necessary to precisely direct gametophyte development.…”

A Multigenic Network of ARGONAUTE4 Clade Members Controls Early Megaspore Formation in Arabidopsis

“…As in the majority of sexual species, in Arabidopsis thaliana ( Arabidopsis ) a single meiotically derived cell [the functional megaspore (FM)] differentiates prior to dividing mitotically and giving rise to the female gametophyte. The nucleus of the FM performs three mitotic divisions generating eight nuclei that subsequently undergo cellularization and differentiation to form accessory cells (the synergids and the antipodals), and two types of gametes: the egg cell and the central cell, which after fertilization will produce the embryo and the endosperm, respectively (Robinson-Beers et al 1992; Reiser and Fischer 1993; Schneitz et al 1995; Sheridan et al 1999; Drews and Yadegari 2002). …”