Genes of Autumn

“Its leaves have been asking it from time to time, in a whisper, ‘When shall we redden?’”
Henry David Thoreau
Autumnal Tints, 1862

By Lee Anna Sherman

The magical transformation of autumn leaves inspires poets and awes observers. But the genetic triggers that produce those stunning colors have long baffled scientists.

Until now.

OSU researchers, studying aspens with scientists in Sweden and Virginia, were seeking a solution to a genetic mystery: What makes trees start reproducing after years of vegetative growth? Their vegetative state can last for more than 10 years before flowering begins, and the scientists wanted to know how trees measure that long timespan.

The international team — including Steven Strauss, a professor of forest science and genetics at OSU — did, indeed, discover which genes control this process. But a surprise turned up: The same genes have another major function in trees’ lives — telling them when to react to shorter days in late summer and fall by beginning the critical process of winter hardening. This is when buds form, chemical changes occur and leaves often turn bright colors, enlivening landscapes.

The gene they focused on, called FLOWERING LOCUS T — FT for short — plays a key role in the control of species’ unique genetic clocks. Through eons of evolutionary adaptations to climatic niches, trees have “learned” to survive via natural selection by knowing when to turn growth on and off. So, as Thoreau observed in his beloved New England countryside, the elm, the sugar maple, the scarlet oak and the aspen all turn color at different times. Genetic adaptations to local climates, the researchers also found, cause different aspen populations to change color at different times, depending on their native latitude.

The study took advantage of the genome sequence of the poplar tree, recently completed by another team that included two OSU graduates, Steve DiFazio and Amy Brunner. Both studies were reported last year in the journal Science.

The findings have promise not only for forestry and horticulture, but also for ecology and conservation, Strauss says. Scientists will be able to advance tree biology more quickly by manipulating the newly identified genetic mechanisms in the lab and studying their inheritance. Practical implications include a better understanding of climatic risks to forests, improvements to the health and yield of fruit trees and solutions to timber shortages.

Strauss is emphatic, however, that substantial social issues must first be resolved. “Because of the tight regulations on even innocuous forms of genetically modified organisms,” he cautions, “it may be difficult to put this knowledge into practice in the near future. It’s therefore as important to work on outreach as it is on advancing the science.”