© 2004 Heron Publishing—Victoria, Canada
Seasonal changes in gene expression at the sapwood–heartwood transition zone of black locust (Robinia pseudoacacia) revealed by cDNA microarray analysis
Jaemo Yang (1), D. Pascal Kamdem (1), Daniel E. Keathley (1) and Kyung-Hwan Han (1, 2)
1. Department of Forestry, 126 Natural Resources, Michigan State University, East Lansing, MI 48824-1222, USA / 2. Corresponding author (hanky@msu.edu) / Received May 12, 2003; accepted May 20, 2003; published online February 2, 2004
Summary
Heartwood is a determining factor of wood quality and understanding the biology of heartwood may allow us to control its formation.
Heartwood formation is a form of senescence that is accompanied by a variety of metabolic alterations in ray parenchyma cells
at the sapwood–heartwood transition zone. Although senescence has been studied at the molecular level with respect to primary
growth, the cell maturation and death events occurring during heartwood formation have been difficult to study because of
their location and timing. Analysis of global gene expression patterns during the transition from sapwood to heartwood may
offer a powerful means of identifying the mechanisms controlling heartwood formation. Previously, we developed cDNA microarrays
carrying 2567 unigenes derived from the bark/cambium region, sapwood and transition zone of a mature black locust tree. Here,
we describe the use of these microarrays to characterize seasonal changes in the expression patterns of 1873 genes from the
transition zone of mature black locust trees. When samples collected in summer and fall were compared, 569 genes showed differential
expression patterns: 293 genes were up-regulated (> twofold) in summer (July 5) and 276 genes were up-regulated in fall (November
27). More than 50% of the secondary and hormone metabolism-related genes on the microarrays were up-regulated in summer. Twenty-nine
out of 55 genes involved in signal transduction were differentially regulated, suggesting that the ray parenchyma cells located
in the innermost part of the trunk wood react to seasonal changes. We established the expression patterns of 349 novel genes
(previously unknown or no-hit), of which 154 were up-regulated in summer and 195 were up-regulated in the fall.
Keywords:
flavonoids, genomics, heartwood extractive, wood formation.
