Pollen tube contents initiate ovule enlargement and enhance seed coat development without fertilization

Kasahara, Ryushiro D.; Notaguchi, Michitaka; Nagahara, Shiori; Suzuki, Takamasa; Susaki, Daichi; Honma, Yujiro; Maruyama, Daisuke; Higashiyama, Tetsuya

doi:10.1126/sciadv.1600554

Cited by 38 publications

(42 citation statements)

References 32 publications

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“…We then performed RNA-seq to analyze the gene expression profiles of the collected the synergid, egg, and central cells in the wild type and the synergid cells in the myb98 mutant (Figure 5D). RNA-seq data from these female gametophyte cells were mapped to the genome of Arabidopsis (TAIR version 10) with the published sequence data from the ovules at 12 hr-after-emasculation (HAE) (Kasahara et al, 2016) and 2-week-old seedlings (Rogers et al, 2012). There were 4,996–18,432 genes (read counts > 10) detected in each sample (Figure 6A; Table S3).…”

Section: Resultsmentioning

confidence: 99%

Dynamics of the cell fate specifications during female gametophyte development inArabidopsis

Susaki

Suzuki

Maruyama

et al. 2020

Preprint

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The female gametophytes of angiosperms contain cells with distinct functions, such as those that enable reproduction via pollen tube attraction and fertilization. Although the female gametophyte undergoes unique developmental processes, such as several rounds of nuclear division without cell plate formation, and the final cellularization, it remains unknown when and how the cell fate is determined during their development. Here, we visualized the living dynamics of female gametophyte development and performed transcriptome analysis of its individual cell types, to assess the cell fate specifications in Arabidopsis thaliana. We recorded time lapses of the nuclear dynamics and cell plate formation from the one-nucleate stage to the seven-cell stage after cellularization, using the in vitro ovule culture system. The movies showed that the nuclear division occurred along the micropylar-chalazal axis. During cellularization, the polar nuclei migrated while associating with forming edge of the cell plate. Then, each polar nucleus migrated to fuse linearly towards each other. We also tracked the gene expression dynamics and identified that the expression of the MYB98pro::GFP, a synergid-specific marker, was initiated before cellularization, and then restricted to the synergid cells after cellularization. This indicated that cell fates are determined immediately after cellularization. Transcriptome analysis of the female gametophyte cells of the wild type and myb98 mutant, revealed that the myb98 synergid cells had the egg cell-like gene expression profile. Although in the myb98, the egg cell-specific gene expressions were properly initiated only in the egg cells after cellularization, but subsequently expressed ectopically in one of the two synergid cells. These results, together with the various initiation timings of the egg cell-specific genes suggest the complex regulation of the individual gametophyte cells, such as cellularization-triggered fate initiation, MYB98-dependent fate maintenance, cell morphogenesis, and organelle positioning. Our system of live-cell imaging and cell-type-specific gene expression analysis provides insights into the dynamics and mechanisms of cell fate specifications in the development of female gametophytes in plants.

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Section: Resultsmentioning

confidence: 99%

Dynamics of the cell fate specifications during female gametophyte development inArabidopsis

Susaki

Suzuki

Maruyama

et al. 2020

Preprint

Self Cite

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“…In angiosperms, the pollen tube releases its contents (including sperm cells) into the embryo sac upon insertion into the ovule, thus completing double fertilization. Recently, Kasahara et al [41,42] reported that the expansion and initiation of seed coat formation occurred even in ovules wherein fertilization failed after pollen tube insertion. This phenomenon was designated as pollen tube-dependent ovule enlargement morphology (POEM), which occurs only when the ovule accepts the pollen tube content (PTC).…”

Section: Pollen Tube-dependent Ovule Enlargement Morphology (Poem)mentioning

confidence: 99%

“…Interestingly, ovules that accepted PTC expanded without fertilization because of cell expansion and division and the production of a partial seed coat, consistent with the results of the transcriptome analysis. Using data from the successful transcriptome analysis, Kasahara et al identified that the novel plant phenomenon POEM occurs only when the ovule accepts PTC, irrespective of fertilization (Figure 7) [41].…”

Section: Pollen Tube-dependent Ovule Enlargement Morphology (Poem)mentioning

confidence: 99%

The Regulation of Sperm Cells Delivery to the Embryo Sac

Kasahara¹

2018

Pollination in Plants

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Pollination, or the first contact between male and female gametophytes, is one of the most important steps in plant reproduction. After pollination, the pollen grains, male gametophytes, are hydrated and then germinate pollen tubes. The pollen tube initially penetrates and grows through the intercellular spaces of the stigma and then grows through the transmitting tract to the placenta connected to an ovule. The pollen tube grows along the surface of the ovule's funiculus, through the micropyle, and into the female gametophyte. After the pollen tube enters the female gametophyte, it ruptures and releases two sperm cells with its contents. The two sperm cells then move toward and fuse with the egg cell and central cell to produce embryo and endosperm, respectively. Multiple sperm cells typically strive to "win the race" and fertilize an egg cell during animal fertilization; however, in flowering plants, each ovule harboring an egg cell generally encounters only one of many pollen tubes conveying plant sperm cells. This chapter mainly addresses reproductive strategies of plants following pollination from the pollen tube extension and the guidance of two sperm cells to the female gametophyte for fertilization in the ovule.

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“…For instance, it was reported that release of sperm cells from the pollen tubes into the embryo sac, no matter whether fertilization is achieved or not, could trigger the division of the central cell, but endosperm development required incorporation of parental genome into the central cell (Aw et al 2010). Recently, by using a sperm cell-associated fertilization defective mutant gcs1þ/À (Mori et al 2006;von Besser et al 2006), Kasahara and his colleagues demonstrated that materials released from the pollen tubes could trigger the ovule enlargement independent of double fertilization (Kasahara et al 2016), and supported the previous conclusion that central cell division requires sperm cell entry into the embryo sac (Aw et al 2010). However, because gcs1pollen tubes, similar to the wild-type (WT) pollen tubes, contain both the cytosol of pollen tube and two sperm cells (Mori et al 2006;von Besser et al 2006), it still remains unsolved whether the signal(s) to initiate ovule enlargement are from the pollen tube or from the sperm cells.…”

mentioning

confidence: 99%

The signals to trigger the initiation of ovule enlargement are from the pollen tubes: The direct evidence

Zhong

Zhang

Liu

2017

JIPB

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Summary In angiosperms, initiation of ovule enlargement represents the start of seed development, the molecular mechanism of which is not yet elucidated. It was previously reported that pollen tube contents, rather than double fertilization, can trigger ovule enlargement. However, it remains unclear whether the signal(s) to trigger the initiation of ovule enlargement are from the sperm cells or from the pollen tubes. Recently, we identified a mutant drop1− drop2−, which produces pollen tubes with no sperm cells. Taking advantage of this special genetic material, we conducted pollination assays, and found that the ovules pollinated with drop1− drop2− pollen could initiate the enlargement and exhibited significant enlarged sizes at 36 h after pollination in comparison with those unpollinated ovules. However, the sizes of the ovules pollinated with drop1− drop2− pollen are significantly smaller than those of the ovules pollinated with wild‐type pollen. These results demonstrate that the pollen tube, rather than the sperm cells, release the signal to trigger the initiation of ovule enlargement, and that double fertilization is required for further enlargement of the seeds.

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Pollen tube contents initiate ovule enlargement and enhance seed coat development without fertilization

Abstract: A new plant ovule enlargement triggered by pollen tube contents, accompanied by seed coat initiation without fertilization.

Cited by 38 publications

References 32 publications

Dynamics of the cell fate specifications during female gametophyte development inArabidopsis

Dynamics of the cell fate specifications during female gametophyte development inArabidopsis

The Regulation of Sperm Cells Delivery to the Embryo Sac

The signals to trigger the initiation of ovule enlargement are from the pollen tubes: The direct evidence

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