How does a tree know it’s autumn? Thanks to its genes, which are turned on and off in a pre-determined order. But in what order? Scientists at Umeå Plant Science Center and the Royal Institute of Technology (KTH) in Stockholm have now brought to light the autumn “genetic timetable” of a tree.

Philosophers like Winnie the Pooh are not the only ones who try to understand what goes on when nature explodes in a pageant of color during the fall. Researchers ask themselves those deep questions too. Trees have a built-in calendar that is governed by the length of the night, and when nights have reached a certain length, a process starts that turns the leaves yellow and red and eventually makes them drop off the tree. However, it is not the length of the night alone that decides what the fall colors will be like. Autumn leaves will take on richer colors if the temperature is low during this process. These developments are governed, as are nearly all other processes in living creatures, by genes, and it is of course important to know how these genes are regulated, that is, when the various genes are turned on or off during the autumn. Researchers at Umeå Plant Science Center and the Royal Institute of Technology (KTH) in Stockholm have discovered the “genetic timetable” of an aspen in the fall.

In order to be able to study this timetable, they have developed a highly specialized aid, a so-called DNA micro-array. This micro-array is a small strip of glass with 13,500 tiny “spots” on it, with each spot consisting of a gene from the aspen. With the aid of this tool, it is possible to follow how all of these thousands of genes are turned on and off during the fall in the leaves of an aspen growing on the Umeå campus. In this way scientists could see how the leave turned on a set of genes that all contributed to the degradation of the constituent parts of the leaf, such as proteins, pigment, and membranes for the purpose of preserving the nutrients for use the following year. At the same time another set of genes were turned off, like those that help the leaf to photosynthesize. These process got under way long before it was possible to see that the leaf was beginning to turn yellow. Of course, the DNA micro-array can be used for studying other processes as well, and Umeå scientists and Stockholm are now trying to understand many different aspects of the “inner life” of a tree. In this, these Swedish researchers have a truly unique resource. No other scientists in the world have access to such a complete micro-array for trees.

The paper is titled “A transcriptional timetable of autumn senescence” and will be published in the next issue of the journal Genome Biology, but it can already be downloaded at http://genomebiology.com/2004/5/4/R24. The article is also commented on in today’s issue of Nature (www.nature.com).