MICROARRAY ANALYSIS IDENTIFIES GENES INVOLVED IN CROWN BUD DORMANCY IN LEAFY SPURGE (EUPHORBIA ESULA L.)

Authors: Horvath, David; Anderson, James; Chao, Wun

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/30/2005
Publication Date: 2/13/2006
Citation: Horvath, D.P., Anderson, J.V., Chao, W.S. Microarray analysis identifies genes involved in crown bud dormancy in leafy spurge (Euphorbia esula L.). [Abstract]. Weed Science Society of America Abstracts 46:92.

Interpretive Summary: The expression of more than 1,500 different genes was studied in crown buds of leafy spurge collected at monthly intervals from August through December as they passed through various stages of dormancy. We identified several different physiological responses correlated with specific stages of dormancy. For example, we observed that development of the photosynthetic apparatus of the buds was “turned on” during October when the buds enter a state of endodormancy (where buds will not grow even if environmental conditions are amenable to growth). We also found evidence that levels of the plant hormone gibberellic acid was reduced during and following endodormancy induction. Finally, we observed changes in expression of flavanoid biosynthesis genes that were previously shown to be “turned off” when dormant buds begin to grow.

Technical Abstract: Leafy spurge is a perennial rangeland weed that has become a model for weed genomics and cross-species research. Microarray analysis allows the simultaneous characterization of the expression from thousands of different genes from any given sampled tissue. We have used microarray analysis to follow changes in gene expression as the buds transition from paradormancy (Aug-Sept) to endodormancy (Sept-Nov) and into ecodormancy (Nov-Dec). Outdoor grown crown buds were collected monthly from Aug through Dec and RNA was isolated from these buds. cDNAs (DNA copies of RNA from expressed genes) were prepared from the crown bud RNA, and labeled with either CY3 or CY5 (fluorescent dyes with different emission spectra). The amount of labeled cDNA from any gene is directly relative to the amount of RNA (level of expression) from that gene in the sampled tissue, and the cDNAs will only stick (hybridize) to their cognate genes on the array. Thus, the level of fluorescence of any gene on the array is indicative of its expression level. cDNA from paradormant greenhouse grown root buds were labeled with a different dye (CY5 if the crown buds were labeled with CY3, or visa versa). The control cDNAs were co-hybridized with the crown bud cDNAs to facilitate comparisons between the different time points. 1st generation microarrays developed from approximately 1,700 leafy spurge and 150 cassava cDNAs (representing approx.1,500 unique genes (unigenes)) were used for these experiments. Our findings indicated that a large number of gibberellic acid (GA)-responsive genes were down-regulated following induction of endodormancy in Sep and Oct., suggesting that GA and abscisic acid (ABA) levels or signal transduction are altered in crown buds during the early fall. Flavaniod biosynthesis gene, previously shown to be down-regulated following loss of paradormancy and suspected of inhibiting auxin transport, are relatively up-regulated during the transition from paradormancy to endodormancy. Finally, in support of earlier findings, Light-Harvesting Chlorophyll-Binding (LHCB) genes have relatively high expression during endodormancy. In addition, several other photomorphogenic genes such as Magnesium-Protoporphyrin Methyltransferase were coordinately regulated with the LHCB genes.