Ethylene in induced conifer defense: cDNA cloning, protein expression, and cellular and subcellular localization of 1-aminocyclopropane-1-carboxylate oxidase in resin duct and phenolic parenchyma cells

Abstract

Members of the Pinaceae family have complex chemical defense strategies. Conifer defenses associated with specialized cell types of the bark involve constitutive and inducible accumulation of phenolic compounds in polyphenolic phloem parenchyma cells and oleoresin terpenoids in resin ducts. These defenses can protect trees against insect herbivory and fungal colonization. The phytohormone ethylene has been shown to induce the same anatomical and cellular defense responses that occur following insect feeding, mechanical wounding, or fungal inoculation in Douglas fir (Pseudotsuga menziesii) stems (Hudgins and Franceschi in Plant Physiol 135:2134-2149, 2004). However, very little is known about the genes involved in ethylene formation in conifer defense or about the temporal and spatial patterns of their protein expression. The enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO) catalyzes the final step in ethylene biosynthesis. We cloned full-length and near full-length ACO cDNAs from three conifer species, Sitka spruce (Picea sitchensis), white spruce (P. glauca), and Douglas fir, each with high similarity to Arabidopsis thaliana ACO proteins. Using an Arabidopsis anti-ACO antibody we determined that ACO is constitutively expressed in Douglas fir stem tissues and is up-regulated by mechanical wounding, consistent with the wound-induced increase of ethylene levels. Immunolocalization showed cytosolic ACO is predominantly present in specialized cell types of the wound-induced bark, specifically in epithelial cells of terpenoid-producing cortical resin ducts, in polyphenolic phloem parenchyma cells, and in ray parenchyma cells.

The role of PnACO1 in light- and IAA-regulated flower inhibition in Pharbitis nil

“…(PnACO1) and determined its sequence. The PnACO1 gene encodes for a protein whose expected molecular mass (34.82 kDa) is similar to that of ACC oxidases identified in other plant species (Hudgins et al 2006;Hunter et al 1999;Nie et al 2001;Vriezen et al 1999;Zanetti et al 2002). The largest similarity with respect to the PnACO1 amino acid sequence As an internal control, we used a constitutively expressed actin gene (83 %) is shown in ACO1 proteins from N. attenuata, N. glutinosa, S. tuberosum, as well as A. thaliana ACO2-69 % (Fig.…”

Expression and β-glucan binding properties of Scots pine (Pinus sylvestris L.) antimicrobial protein (Sp-AMP)

“…Ethylene signalling has been implicated in induced cellular and chemical defences in conifers, and is vital in the activation of cells specialized for the formation of defence-related terpenoids and phenolics in the outermost bark and phloem tissues (Hudgins et al 2006).…”

Producing the Ethylene Signal: Regulation and Diversification of Ethylene Biosynthetic Enzymes

“…3) and the innovation of posttranslational regulatory switches controlling ACS stability very early in flowering plant evolution. Conifers express ACO isoforms that group phylogenetically with the angiosperm ACOs known to synthesize ethylene as well as additional ACO-like isoforms, indicating that diversification of ACO isoforms occurred prior to the split of flowering plants and gymnosperms (Hudgins et al, 2006;Rudu s et al, 2013). The conservation of ACS and ACO isozymes in conifers suggests that the flowering plant ethylene biosynthesis pathway is conserved throughout seed plants, although the posttranslational regulation of specific isoforms likely differs between gymnosperms and angiosperms, because the gymnosperm ACS isoforms exhibit none of the known regulatory sequence motifs.…”

“…tomato ACO1-3 [Hamilton et al, 1991;Bidonde et al, 1998], MdACO1 from apple [Malus domestica; Dong et al, 1992], and Arabidopsis ACO4 [Gómez-Lim et al, 1993]) are known to exhibit ACC oxidase activity in vitro. Arabidopsis ACO2 and ACO3 and tomato ACO4 group with these active ACOs in phylogenetic analyses along with some conifer enzymes, whereas tomato ACO5 and Arabidopsis ACO1 and ACO5 cluster together in a sister clade that is separate from the group of enzymatically defined ACO isoforms (Hudgins et al, 2006;Rudu s et al, 2013). Furthermore, a set of Arabidopsis dioxygenase gene products with a more distant relationship to the known ACOs (Rudu s et al, 2013) have been designated as ACO6 to ACO13 on the basis of sequence similarity alone (Clouse and Carraro, 2014).…”