Ed

The most ancient divergence within the plant actin gene tree occurred approximately 350 MYA, separating vegetative and reproductive actins. A phylogram of the eight expressed Arabidopsis actins is shown below.
	Two of the vegetative actins ACT2 & ACT8 appear to be evolving faster suggesting they are less subject to selective constraint. They are expressed primarily in roots, shoots, sepals, and petals, which may be the most recently evolved plant organs. ACT7 is expressed in rapidly expanding tissues and responds to most phytohormones.   ACT11 is expressed in ovule, embryo, seed, silique, and pollen making it the most widely expressed reproductive actin. Based on its low rate of evolution it may be most similar to ancient forms of plant and algal actin.   The four late pollen actins 1, 3, 4, & 12 are distinct by 220 MYA- about the time that Gnatales and the Angiosperms have a common ancestor. The divergence of the vegetative from reproductive actins from a common ancestral sequence is estimated to have occured between 350 and 450 million years ago. The evolution and divergence of the late pollen actins from an older class of reproductive actins has been more accurately estimated at 220 million years ago, just prior to the origin of the angiosperms.

Meagher et al., 1999; Kandasamy et al., 2000; McDowell et al., 1996

Previous Page

Next Page