Abstract
HEXOKINASE1 (HXK1) from Arabidopsis (Arabidopsis thaliana) has dual roles in glucose (Glc) signaling and in Glc phosphorylation. The cellular context, though, for HXK1 function in either process is not well understood. Here we have shown that within normal experimental detection limits, AtHXK1 is localized continuously to mitochondria. Two mitochondrial porin proteins were identified as capable of binding to overexpressed HXK1 protein, both in vivo and in vitro. We also found that AtHXK1 can be associated with its structural homolog, F-actin, based on their coimmunoprecipitation from transgenic plants that overexpress HXK1-FLAG or from transient expression assays, and based on their localization in leaf cells after cryofixation. This association might be functionally important because Glc signaling in protoplast transient expression assays is compromised by disruption of F-actin. We also demonstrate that Glc treatment of Arabidopsis seedlings rapidly and reversibly disrupts fine mesh actin filaments. The possible roles of actin in HXK-dependent Glc signaling are discussed.
Highlights
HEXOKINASE1 (HXK1) from Arabidopsis (Arabidopsis thaliana) has dual roles in glucose (Glc) signaling and in Glc phosphorylation
We have further examined the cellular context for HXK function in Glc signaling. These studies establish that mitochondrialbound HXK can interact with actin and that a normal functioning actin cytoskeleton is required for some HXK-dependent Glc signaling in transient expression assays
We used several approaches to test whether AtHXK1 is bound to mitochondria and whether it might dissociate and/or move to the nucleus under a range of treatments
Summary
HEXOKINASE1 (HXK1) from Arabidopsis (Arabidopsis thaliana) has dual roles in glucose (Glc) signaling and in Glc phosphorylation. On the other hand, based on a protoplast lysis protocol using Triton X-100, Yanasigawa et al (2003) reported that AtHXK1 occurs at least in part in the nucleus of isolated protoplasts This has led to a current model of Glc signaling that suggests that HXK-dependent plant Glc signaling occurs in analogous fashion to that observed in yeast (Rolland et al, 2006), in which a nuclear form of HXK acts as a transcriptional regulator. HXK-dependent Glc signaling involves transcriptional control, and translational and posttranslational processes (Ho et al, 2001; Yanasigawa et al, 2003) With this in mind, we have further examined the cellular context for HXK function in Glc signaling. Our data link actin cytoskeleton functions in plant growth with HXK-dependent Glc signaling
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