Auxin is present in varying concentrations in plant cells and tissues. The
speed of plant growth, especially at the top, development of lateral shoots
and roots, leaves, flowers and fruits are set in motion by the hormone
auxin. It's still a mystery how all these processes are made possible by
this age-old molecule, and how such a complex system came about.
PhD candidate at Wageningen University and Research, Sumanth Mutte, studied
the genome of over a thousand plant species. He selected species that are
all still alive, but which have a different evolutionary life history. This
includes the 'modern' flowering plants that split off 320 million years ago
and which now have a highly complex auxin system, older seed plant types
such as conifers, and spore plants such as ferns and the earlier mosses,
which are over half a billion years old. The oldest form of life studied for
auxin were single-cell, green algae, dating back to the deep past of a
billion years ago.
Research leader Dolf Weijers said that of the three protein families that
mediate auxin functions, one was already present in the green algae. Digging
even deeper, a billion years ago, their research led to fragments of the
three protein families. "We still find them in the plants of today, but they
originate from green algae and probably had a different function at first,"
Professor Weijers added.
Postdoctoral researcher Hirotaka Kato subsequently conducted 'experimental
genome archaeology' with plants from the three different eras: algae,
mosses, and ferns. The researcher studied how these genomes respond to
auxin, by determining the number of genes that are turned on or off by the
hormone, for instance. "This shows us how the auxin system has become more
complex, and which components plants can modify to use the hormone for new
processes to regulate its growth and shape," explains Professor Weijers.