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U.S. Department of Agriculture USDA Forest Service Southern Regional Extension Forestry Southern Regional Extension Forestry

Genetic Control of Heartwood Formation in Black Walnut

We are investigating the spatial and temporal regulation of heartwood formation in black walnut (Juglans nigra L.), one of the most valuable fine hardwood species. We extracted total RNA from the transition zone (TZ) and other tissues of black walnut from replicate trees in two seasons (summer and fall) in each of two years. Hybridizing black walnut TZ cDNA to a poplar microarray led to the identification of candidate genes associated with transcriptional regulation of heartwood formation. After preliminary screening using semi-quantitative RT-PCR, three genes from black walnut were characterized more fully: JnRAP2-like, an AP2 domain-containing transcription factor similar to ethylene response element-binding proteins; JnKNAT3-like, a KNOTTED-LIKE3 transcription factor containing two KNOX domains and a homeodomain; and JnCML-like, a gene predicted to encode a protein with two EF-hand motifs. Transcripts from all three were found to be more abundant in the TZ when compared to other xylem tissues; however, none of the three genes were expressed at high levels in senescing leaves, indicating that plant cell death (PCD) processes in xylem may differ from leaf senescence.

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Author(s): C. -J Tsai, K. E. Woeste, R. Meilan, S. A. Harding, Z. Huang

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 2009