Science and Reason: Our plant relatives

Humans aren't related merely to other animals – plants are kinfolk too. In fact, we share some genes with ancestors of both animals and plants, genes not found even in most modern plants.

Green Algae: The Nexus Of Plant-Animal Ancestry

Genes of a tiny, single-celled green alga called Chlamydomonas reinhardtii may contain scores more data about the common ancestry of plants and animals than the richest paleontological dig. This work is described in an article in Science.

A group of researchers, including Arthur Grossman of the Carnegie Institution, report on the results of a major effort to obtain the full library of genes, or the genome sequence, of Chamydomonas and to compare its ~15,000 genes to those of plants and animals, including humans. The research shows that this alga has maintained many genes that were lost during the evolution of land plants, has others that are associated with functions in humans, and has numerous genes of unknown function, but which are associated with critical metabolic processes.

In particular, cilia are important structures of some eukaryotic cells, are inherited from the common ancestor of plants and animals. Cilia are found in animal cells, analogous to flagella in Chamydomonas, but have no analogue in most plant cells.

Chlamydomonas, affectionately called Chlamy, is an alga of 10 micrometres in size that is present in soil and freshwater environments. It performs photosynthesis like plants, but it diverged evolutionarily from flowering land plants about 1 billion years ago. It is even more distantly related to animals (the split between animals and plants was ~1.6 billion years ago). Chlamy moves using two anterior, hair-like flagella that were lost by its cousins, the flowering land plants, after the evolutionary split of the two lineages. The flagella are equivalent to the cilia and centrioles in animal cells. Centrioles are structures involved in cell division; they form a spindle apparatus, which helps separate genetic material into two new cells during mitosis. Cilia are important to many animal functions.