Recorded: 20 Feb 2001
Epigenetics has been an interest of mine for a long time. Epigenetics is difficult to define. Actually, these days it has a different definition than the one the ancient Greeks gave it or for that matter that [Conrad] Waddington, who was an English developmental biologist in the 1940s, gave it initially. Nowadays, we think about epigenetics as the study of heritable changes. They are either heritable through mitosis or through meiosis, actually more rarely through meiosis. But heritable changes that do not involve changes of the DNA sequence, so some other change, like a chromosome change or a change in the modification of the DNA—methylation—this is what we mean by epigenetics. There are many different mechanisms involved in epigenetics, but they're beginning to coalesce around a few different key areas. Their impact on plant development, and especially certain key aspects of plant development, is really what we look at. So plants, in common with animals, have a set of stem cells, which essentially are the derivatives, are the initials, from which all the derivatives of the plant effectively arise. These stem cells retain their own identity during division, but their daughters go on to make leaves and flowers and so on. The ability of the genome to organize and coordinate that change between stem cells and daughter cells or founder cells, that change and the way the genome influences that, is something that is just beginning to be possible to be addressed now. So we have a number of mutations that affect the interaction between the founders and the stem cells. They're mutations in highly conserved genes. They're genes that are typically found in animals as well as in yeast and fungi as well as plants, and they're probably related to fundamental properties of the stem cells.
Stem cells in animals, of course, are very trendy these days, with the cloning of Dolly the sheep, not to mention the ability to actually use stem cells to study cancer or neurodegenerative diseases and so on. In plants, stem cells have a very long history. The meristem in plants is a structure that was recognized in the 19th century actually, probably before, as being a group of undifferentiated cells that had this essential property of being able to maintain themselves over many generations. If you think of a redwood tree for example, the stem cells there have maintained themselves in that epigenetic state over literally thousands of years. Plants have an extraordinary ability to make this distinction between stem cells and founder cells. In that sense, plants don't age in the way that animals do and similarly plants have a way of being able to produce germ cells from their stem cells throughout development and that's another key thing. So plants are much more sensitive to the environment, and the environment might even have genetic or epigenetic effects on the germ cells. This is almost heresy! This is like Lamarck or something like that. Well, it's not quite the way Lamarck envisioned it but nonetheless there's a lot of impact of this sort of research on the way in which we think about evolution. And I think plants are really at the forefront of that.
So, yes, we're working with a number of mutations actually, in both maize and Arabidopsis that affect stem cells. In fact, behind you there's one of [the] maize [mutations].
Rob Martienssen is a plant molecular geneticist and professor at Cold Spring Harbor Laboratory. He received his Ph.D. from Cambridge University in 1986 and did postdoctoral research at the University of California, Berkeley.
As a young scientist, he worked closely with Barbara McClintock. He currently studies plant epigenetics and development using functional genomics. He was awarded the Kumho International Science Award in Plant Biology and Biotechnology (2001).