DNA methylation changes during plant development

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发布日期：2012-09-20 20:53 文章来源：丁香园
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Diagram of an Arabidopsis (A) flower, and (B) the male and female gametophytes. Male

gametogenesis occurs in stamens (St) and generates tricellular pollen grains that contain a

vegetative nucleus (VN) and two sperm cells (SC). Female gametogenesis occurs in ovules

(Ov) and produces a multicellular gametophyte with three antipodal cells (AC), two

synergid cells (SC), one egg cell (EC) and a diploid (2n) central cell nucleus (CCN)78.

(upper) Model showing transposon reactivation and siRNAs production specifically in the

VN. These siRNAs may travel to the SCs to reinforce transposon silencing. (lower) Model

showing siRNAs in the CCN, which may arise as a consequence of global demethylation.

These siRNAs may travel to the EC and reinforce silencing. Reinforced silencing in the

sperm and egg cells could account for the observed hypermethylation of the embryo. (C)

Fertilization of the EC and CCN generate the embryo and endosperm, respectively. The

embryo will give rise to the mature Arabidopsis plant while the endosperm is a terminally

differentiated tissue. Imprinting is observed the endosperm, which nourishes the embryo,

and is thus analogous to the placenta in mammals, where imprinting also occurs. In plants,

maternal imprinting results from demethylation in the CCN by the DME glycosylase, which

likely accounts for the observed hypomethylation in this tissue. After fertilization, the

unmethylated (open circles) maternal alleles (♀) are expressed in the endosperm, while the

paternal allele (♂) is methylated (closed circles) and silent.

编辑: gaowei2010

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