Generative Cell Morphogenesis

Cell migration plays a key role in exploiting positional information to specify cell fate and differentiation in early animal development. Plant development and cell specification is also strongly dependent on positional information, however plant cells are constrained by rigid pecto-cellulosic walls and so cannot move in response to local cues.

A remarkable exception to this rule occurs during microgametogenesis wherein a unique intracellular migration of the generative cell occurs. Generative cell migration follows the asymmetric division of the microspore at pollen mitosis I which generates the large vegetative cell and smaller generative cell separated by a dividing callose wall. After division the callose wall is degraded and the generative cell undergoes morphogenic changes resulting in detachment from the intine wall layer and inward migration into the cytoplasm of the vegetative cell to create a unique 'cell within a cell' structure - the pollen grain.

Intracellular migration of the generative cell is necessary for the directional transport of the sperm cells to the embryo sac (sperm cells are non-motile in flowering plants and are transported within the pollen tube cytoplasm). The free movement and intimate association between the vegetative and germ cells therefore play a vital role in microgametogenesis, male fertility and seed production.

We have identified several Arabidopsis mutants in which migration of the germ cell is blocked, leaving the generative or sperm cells marginalised outside the vegetative cell. These mutants provide a unique opportunity to identify molecular components involved in generative cell functions and morphogenesis.

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