Abstract
The correct development of a diploid sporophyte body and a haploid gametophyte relies on a strict coordination between cell divisions in space and time. During plant reproduction, these divisions have to be temporally and spatially coordinated with cell differentiation processes, to ensure a successful fertilization. Armadillo BTB Arabidopsis protein 1 (ABAP1) is a plant exclusive protein that has been previously reported to control proliferative cell divisions during leaf growth in Arabidopsis. Here, we show that ABAP1 binds to different transcription factors that regulate male and female gametophyte differentiation, repressing their target genes expression. During male gametogenesis, the ABAP1-TCP16 complex represses CDT1b transcription, and consequently regulates microspore first asymmetric mitosis. In the female gametogenesis, the ABAP1-ADAP complex represses EDA24-like transcription, regulating polar nuclei fusion to form the central cell. Therefore, besides its function during vegetative development, this work shows that ABAP1 is also involved in differentiation processes during plant reproduction, by having a dual role in regulating both the first asymmetric cell division of male gametophyte and the cell differentiation (or cell fusion) of female gametophyte.
Highlights
The life cycle of higher plants alternates between the growth of a diploid sporophytic body and a haploid gametophytic form
We showed that Armadillo BTB Arabidopsis protein 1 (ABAP1) is expressed in both male and female gametophytes and that ABAP1 imbalance impairs both male and female gametogenesis
ABAP1 is involved in the regulation of both formative cell division in male gametophyte and cell differentiation in female gametophyte, two processes that are essential for a successful plant reproduction in Arabidopsis
Summary
The life cycle of higher plants alternates between the growth of a diploid sporophytic body and a haploid gametophytic form. The correct development of both generations relies on a strict coordination between cell division and cell differentiation in space and time (Harashima and Schnittger, 2010). The formative and asymmetric divisions generate daughter cells of distinct sizes and identities, having an important role in the differentiation of cell types (Kajala et al, 2014). A proper temporal and spatial coordination between cell division and differentiation during development of both gametophytes is essential for a successful plant reproduction. ABAP1 Role in Gametophyte Development asymmetric mitotic cell divisions participate in the differentiation of male gametophyte, by forming a large vegetative cell (VC) and a small generative cell (GC) that subsequently divides symmetrically, forming the two sperm cells (Borg and Twell, 2010; Twell, 2011). The cellular dynamics of male and female gametogenesis are well described, the underlying molecular and biochemical mechanisms temporally coordinating both processes remain to be elucidated
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