A model genetic system, the fern Ceratopteris richardii

The fern Ceratopteris richardii is useful as a plant model genetic system, as is the flowering plant Arabidopsis thaliana. Comparisons of the genomes and proteomes of plants help to highlight the genetic changes that occurred during plant evolution.

For example, experts have reported the results of a study of the expression of nearly 4,000 genes during spore germination in C. richardii. They identified genes that were expressed by both fern spores and germinating flowering plant seeds or pollen, a type of spore. One such gene is associated with the role of peroxisomes in making the cellular transition from dormancy to active metabolism, and others are related to cellular use of calcium ions and nitrous oxide (NO) as signalling molecules. In ferns, NO helps the long, thin cells known as rhizoids to perceive gravity, with the result that these elongate cells grow downward at their tips. Such downward growth enables rhizoids to anchor gametophytes in a position that helps to keep gametangia and gametes from drying out. In this way, rhizoid growth fosters the production of embryos, thereby increasing plant fitness. Comparative genomic or proteomic studies suggest how the evolutionary process of descent with modification has generated the reproductive features of the seed plants on which people greatly depend.