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PLANTS INTERACTING WITH OTHER ORGANISMS

Aminocyclopropane Carboxylic Acid Synthase Is a Regulated Step in Ethylene-Dependent Induced Conifer Defense. Full-Length cDNA Cloning of a Multigene Family, Differential Constitutive, and Wound- and Insect-Induced Expression, and Cellular and Subcellular Localization in Spruce and Douglas Fir^1,2,[W],[OA]

Michael Smith Laboratories (S.G.R., J.W.H., S.J., J.B.) and Departments of Botany and Forest Sciences (J.B.), University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4; and School of Biological Sciences, Washington State University, Pullman, Washington 99164–4236 (J.W.H., V.R.F.)

In conifer stems, formation of chemical defenses against insects or pathogens involves specialized anatomical structures of the phloem and xylem. Oleoresin terpenoids are formed in resin duct epithelial cells and phenolics accumulate in polyphenolic parenchyma cells. Ethylene signaling has been implicated in the induction of these chemical defenses. Recently, we reported the cloning of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) from spruce (Picea spp.) and Douglas fir (Pseudotsuga menziesii). ACO protein was constitutively expressed in Douglas fir and only weakly induced upon wounding. We now cloned seven full-length and one near full-length cDNA representing four distinct 1-aminocyclopropane-1-carboxylic acid synthases (ACS; ACS1, ACS2, ACS3, and ACS4) from spruce and Douglas fir. Cloning of ACS has not previously been reported for any gymnosperm. Using gene-specific, quantitative real-time polymerase chain reaction, we measured constitutive expression for the four ACS genes and the single-copy ACO gene in various tissues of Sitka spruce (Picea sitchensis) and in white spruce (Picea glauca) somatic embryos. ACO and ACS4 were ubiquitously expressed at high levels; ACS1 was predominantly expressed in developing embryos and ACS2 and ACS3 were expressed only at very low levels. Insect attack or mechanical wounding caused strong induction of ACS2 and ACS3 in Sitka spruce bark, a moderate increase in ACO transcripts, but had no effect on ACS1 and ACS4. ACS protein was also strongly induced following mechanical wounding in Douglas fir and was highly abundant in resin duct epithelial cells and polyphenolic parenchyma cells. These results suggest that ACS, but not ACO, is a regulated step in ethylene-induced conifer defense.

² This paper is dedicated to the memory of Dr. Vincent R. Franceschi.

³ These authors contributed equally to the paper.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jörg Bohlmann (bohlmann{at}interchange.ubc.ca).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.089425

^* Corresponding author; e-mail bohlmann{at}interchange.ubc.ca; fax 604–822–2114.

Received September 3, 2006; accepted November 17, 2006; published November 22, 2006.

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