Identification and characterization of genes involved in heartwood formation in black walnut (Juglans nigra L.)
Abstract
The value of black walnut (Juglans nigra L.) is determined by the quality and quantity of darkly-colored heartwood in its stem. We are exploring the regulation of heartwood production by identifying genes associated with the transition from sapwood to heartwood. First, a cross-species microarray data analysis was performed using an aspen 7K gene array. Results showed that only about 17% (1,253 vs. 7K) of the probes in the microarray hybridized with genes from black walnut. Most of the genes that hybridized were unclassified or “no hits” but some, such as the orthologs of At2g14900 and At3g04710, were putatively related to cell rescue and defense. To isolate and identify additional genes associated with heartwood formation, we characterized the expression of 80 ESTs putatively associated with heartwood formation in the transition zone (TZ) of black walnut. Semi-quantitative RT-PCR and real-time PCR were performed to detect expression changes of candidate genes in the TZ and sapwood of trees harvested in summer and fall. Results revealed that the three clones, a presumed homeobox protein Knotted-1-like 3 (designated JnKNAT3-like), a single AP2-containing domain protein (designated JnRAP2-like), and an EF-hand motif containing protein (designated JnCML-like), were highly expressed in the TZ when compared to other wood tissues. The expression pattern of these three transcripts was investigated in the pith meristem, roots, embryogenic callus, vascular cambium, female flowers, male flowers, green leaves, and partially and fully senescent leaves of black walnut. Transcript abundance varied considerably among tissues. Functional analysis of JnRAP2-like was further characterized in the model plant species Arabidopsis thaliana and INRA 717-1B4 (Populus tremula x P. alba). Over-expression (OE) of JnRAP2-like in transgenic Arabidopsis thaliana revealed that JnRAP2-like, like other members of ERF family, may interact with the ethylene, jasmonate, and abscisic acid signaling pathways during heartwood formation. Overall, these analyses provide preliminary insight into the mechanism regulating heartwood formation in black walnut.
Degree
Ph.D.
Advisors
Woeste, Purdue University.
Subject Area
Forestry|Plant sciences
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.