We have developed genomic tools to allow the genus Populus
(aspens and cottonwoods) to be exploited as a full-featured
model for investigating fundamental aspects of tree biology. We
have undertaken large-scale expressed sequence tag (EST)
sequencing programs and created Populus microarrays with
significant gene coverage. One of the important aspects of plant
biology that cannot be studied in annual plants is the gene
activity involved in the induction of autumn leaf senescence. On
the basis of 36,354 Populus ESTs, obtained from seven cDNA
libraries, we have created a DNA microarray consisting of 13,490
clones, spotted in duplicate. Of these clones, 12,376 (92%) were
confirmed by resequencing and all sequences were annotated and
functionally classified. Here we have used the microarray to
study transcript abundance in leaves of a free-growing aspen
tree (Populus tremula) in northern Sweden during natural autumn
senescence. Of the 13,490 spotted clones, 3,792 represented
genes with significant expression in al