Abstract
Unlike animals, where the germline is established early during embryogenesis, plants set aside their reproductive lineage late in development in dedicated floral organs. The specification of pollen mother cells (PMC) committed to meiosis takes place in the sporogenous tissue in anther locules and marks the somatic-to-reproductive cell fate transition toward the male reproductive lineage. Here we show that Arabidopsis PMC differentiation is accompanied by large-scale changes in chromatin organization. This is characterized by significant increase in nuclear volume, chromatin decondensation, reduction in heterochromatin, eviction of linker histones and the H2AZ histone variant. These structural alterations are accompanied by dramatic, quantitative changes in histone modifications levels compared to that of surrounding somatic cells that do not share a sporogenic fate. All these changes are highly reminiscent of those we have formerly described in female megaspore mother cells (MMC). This indicates that chromatin reprogramming is a common underlying scenario in the somatic-to-reproductive cell fate transition in both male and female lineages.
Highlights
In flowering plants, sexual reproduction involves the differentiation of spore mother cells (SMC) in dedicated male and female floral organs
Chromatin decondensation in Arabidopsis pollen mother cells (PMC) In flowering plants, the development of the male reproductive lineage is initiated with the differentiation of PMC in the early anther locule
This is accompanied by a 47.9% decrease in heterochromatin content (Figure 1C; Supplementary Material Table S1) and reduction in the mean number of distinct chromocenters from ca. 7 down to 3 in average in PMC (Figure 1D)
Summary
Sexual reproduction involves the differentiation of spore mother cells (SMC) in dedicated male and female floral organs. Male SMC in the anthers give rise to haploid microspores through meiosis. The latter undergo mitosis and generate a bicellular, tricellular male gametophyte encapsulated in the pollen grain. Male SMC are referred to as pollen mother cells (PMC) or microspore mother cells in the literature. The mature male gametophyte comprises a large vegetative cell and two sperm cells. The vegetative cell grows a pollen tube delivering the sperm cells to the ovule. Each of the sperm cells will fuse with the female gametes, the egg and central cell, to generate the zygote and endosperm, respectively, following double fertilization (Maheshwari, 1950; Twell, 2011)
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