Ethylene Genetics

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Abstract Hormones play an important role in plant growth and development. Ethylene is one such hormone and the past decade has seen major components of the ethylene response pathway in plants being identified and characterized. Ethylene regulates responses at a number of levels and molecular genetic analysis of ethylene signaling in Arabidopsis thaliana has identified a number of gentic loci that encode proteins involved in the ethylene response. Elements of the pathway, which have been characterized include: the two-component-like receptors (ETR1, ETR2, ERS1, ERS2 & EIN4), the Raf-like kinase (CTR1), the transcription factor (EIN3) and the ethylene response element binding proteins (EREBPs). A linear model is now in place, which links all these elements together and demonstrates how they interact and ultimately how ethylene signaling operates.

INTRODUCTION Ethylene, a simple olefin has been shown to display a role in how plants respond to a diverse array of environmental signals. Throughout a plants life cycle ethylene affects fruit ripening, germination, cell expansion and elongation, senescence, leaf abscission and even sex determination.

All of these responses are controlled by various signal transduction pathways, which ethylene regulates. The ethylene biosynthetic pathway often referred to as the "Yang Cycle" has been very well characterized. Aminocyclo-propane-1-carboxy acid (ACC) oxidase and ACC synthase are the two enzymes, which regulate the cycle. The genes responsible for these enzymes have also been cloned in many species of plant. (Grierson et al, 1991 & Van der Straeten et al, 1990 respectively) A bioassay known as the Triple Response has been used to perform a large number of screens, which have provided the identification of genes, which are involved in the ethylene response pathway (Guzman & Ecker, 1990). First demonstrated in pea seedlings by Neljubow in 1901 (Johnson & Ecker, 1998) which when grown in the dark but...