Poster: Signaling, cell-to-cell

Abs # 430: Characterization of Arabidopsis Hexokinase-Like Genes in Glucose Signaling

Presenter:	Moore, Brandon , moore8@clemson.edu
Authors	Metters, Helen  (A)   Sheen, Jen  (B)   Moore, Brandon  (A)
Affiliations:	(A): Clemson University (B): Massachusetts General Hospital

Hexokinase (HXK)-dependent glucose signaling affects plant growth throughout the life cycle. In Arabidopsis, HXK exists as a family of 6 genes. The highly homologous AtHXK1 and AtHXK2 genes have been previously cloned and their proteins shown to have both hexose phosphorylation activity and glucose signaling activity. The remaining 4 HXK-like (HKL) genes are only about 50% identical to AtHXK1, but 3 of these do have a conserved sugar binding domain and catalytic signature motif. Here we report on the cloning and initial functional characterization of the HKL genes. Organ transcript profiles by RT-PCR indicate that all occur in relative low abundance. Three of the HKL genes are most prominently expressed in different sink organs including roots and flowers, while one is expressed only in flowers. We have used protoplast transient expression assays to characterize their functional properties. Only one of the 4 proteins has detectable catalytic activity (HXK3) and was shown by bio-imaging to be targeted to plastids. Of the catalytically inactive proteins, one is predicted not to bind sugar and the other 2 not to bind ATP. The latter 2 (HKL1 and HKL2) plus HXK1 and HXK2 are all targeted to the mitochondria and all exclusively have an N-terminal domain of 20-24 amino acids, predicted to be a membrane anchor. Available evidence indicates that all of the mitochondrial localized HXKs and HKLs likely function in glucose signaling. AtHKL2p interacts with AtHXK1 by co-immunoprecipation assay and activates glucose signaling in transient expression assays. Transgenic lines with altered AtHKL2p and AtHKL1p both have growth phenotypes on agar plates with exogenous glucose that are associated with altered glucose sensing. Soil phenotypes in most cases are similar to parental lines.