The structure that directly precedes the development of both a male and female gametophyte is the spore.

Here's why:

* Spores are haploid cells produced by meiosis in the sporophyte generation of plants.

* Male gametophytes develop from microspores (also called pollen grains).

* Female gametophytes develop from megaspores.

So, the spore is the single-celled precursor to both the male and female gametophytes.