Sir-dependent downregulation of various aging processes

Daniel, Jacques H.

doi:10.1007/s00438-005-0040-5

Cited by 10 publications

(12 citation statements)

References 59 publications

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“…cerevisiae and A . nidulans (Daniel, 2005; Bernardo et al , 2007) and also in Arabidopsis (Karve et al , 2008). Whether non-catalytic homologues of known enzymes are commonly present in other protein families is not known.…”

Section: Discussionmentioning

confidence: 99%

“…The fungal HKL proteins have divergent roles including one as a meiosis-specific transcription factor in Saccharomyces cerevisiae (Daniel, 2005) and others as regulators of a carbon starvation response in Aspergillus nidulans (Bernardo et al , 2007). Despite the reports of the presence of HKL proteins in evolutionarily diverse species, their lack of catalytic activity has made it challenging to define their functions.…”

Section: Introductionmentioning

confidence: 99%

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Function of Arabidopsis hexokinase-like1 as a negative regulator of plant growth

Karve

Moore

2009

Journal of Experimental Botany

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A recent analysis of the hexokinase (HXK) gene family from Arabidopsis revealed that three hexokinase-like (HKL) proteins lack catalytic activity, but share about 50% identity with the primary glucose (glc) sensor/transducer protein AtHXK1. Since the AtHKL1 protein is predicted to bind glc, although with a relatively decreased affinity, a reverse genetics approach was used to test whether HKL1 might have a related regulatory function in plant growth. By comparing phenotypes of an HKL1 mutant (hkl1-1), an HXK1 mutant (gin2-1), and transgenic lines that overexpress HKL1 in either wild-type or gin2-1 genetic backgrounds, it is shown that HKL1 is a negative effector of plant growth. Interestingly, phenotypes of HKL1 overexpression lines are generally very similar to those of gin2-1. These are quantified, in part, as reduced seedling sensitivity to high glc concentrations and reduced seedling sensitivity to auxin-induced lateral root formation. However, commonly recognized targets of glc signalling are not apparently altered in any of the HKL1 mutant or transgenic lines. In fact, most, but not all, of the observed phenotypes associated with HKL1 overexpression occur independently of the presence of HXK1 protein. The data indicate that HKL1 mediates cross-talk between glc and other plant hormone response pathways. It is also considered Whether a possibly decreased glc binding affinity of HKL1 could possibly be a feedback mechanism to limit plant growth in the presence of excessive carbohydrate availability is further considered.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Function of Arabidopsis hexokinase-like1 as a negative regulator of plant growth

Karve

Moore

2009

Journal of Experimental Botany

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“…EMI2 is a cytoplasmic protein that is required for induction of early meiosis-specific transcription factor IME1 and sporulation while the function and subcellular location of YLR446W is unknown (Enyenihi and Saunders 2003; Saccharomyces Genome Database, http://www.yeastgenome.org/). EMI2 has also been shown to act as an antagonist to Sir2p, a histone deacetylase involved in chromatin silencing and regulation of cell aging (Daniel 2005). Phylogenetic analysis of fungal hexokinases using the distance method showed that YLR446W, but not EMI2, clusters with HxkC and HxkD (Fig.…”

Section: Regulation Of the Hxkd Transcriptmentioning

confidence: 98%

Characterization of regulatory non-catalytic hexokinases in Aspergillus nidulans

et al. 2007

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Hexokinases catalyse the first step in glucose metabolism and play a role in glucose sensing in mammals, plants and fungi. We describe a new class of hexokinases that appear to be solely regulatory in function. The Aspergillus nidulans hxkD gene (formerly named xprF) encodes a hexokinase-like protein. We constructed hxkDDelta gene disruption mutants which showed increased levels of extracellular protease in response to carbon starvation. The hxkDDelta mutations are not completely recessive, indicating that the level of the gene product is critical. Transcript levels of hxkD increase during carbon starvation and this response is not dependent on functional HxkD. A gene encoding a second atypical hexokinase (HxkC) was identified. The hxkCDelta gene disruption mutant exhibits a phenotype similar, but not identical, to hxkDDelta mutants. As with hxkD, mutations in hxkC are suppressed by loss-of-function mutations in xprG, which encodes a putative transcriptional activator involved in the response to nutrient limitation. We show that GFP-tagged HxkD was found only in nuclei suggesting a regulatory role for HxkD. GFP-tagged HxkC was associated with mitochondria. Homologs of hxkC and hxkD are conserved in multi-cellular fungi. Genes encoding atypical hexokinases are present in many genome sequence databases. Thus, non-catalytic hexokinases may be widespread.

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“…The metabolic only catalysts include yeast HXK1 and glucokinase1 (Santangelo 2006), and we suggest might also include plant plastid HXKs. Among non-catalytic HKL proteins, there are two HKL proteins in S. cerevisiae (Bernardo et al 2007), one of which, EMI2, is required for induction of a meiosis-specific transcription factor (Daniel 2005). In A. nidulans, the non-catalytic proteins AnHXKC and AnHXKD both are thought not to have a role in glucose signaling, but genetic evidence indicates that instead both are negative regulators for a secreted extracellular protease during carbon starvation (Bernardo et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Expression and evolutionary features of the hexokinase gene family in Arabidopsis

Karve

Rauh

Xia

et al. 2008

Planta

112

141

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Arabidopsis hexokinase1 (HXK1) is a moonlighting protein that has separable functions in glucose signaling and in glucose metabolism. In this study, we have characterized expression features and glucose phosphorylation activities of the six HXK gene family members in Arabidopsis thaliana. Three of the genes encode catalytically active proteins, including a stromal-localized HXK3 protein that is expressed mostly in sink organs. We also show that three of the genes encode hexokinase-like (HKL) proteins, which are about 50% identical to AtHXK1, but do not phosphorylate glucose or fructose. Expression studies indicate that both HKL1 and HKL2 transcripts occur in most, if not all, plant tissues and that both proteins are targeted within cells to mitochondria. The HKL1 and HKL2 proteins have 6-10 amino acid insertions/deletions (indels) at the adenosine binding domain. In contrast, HKL3 transcript was detected only in flowers, the protein lacks the noted indels, and the protein has many other amino acid changes that might compromise its ability even to bind glucose or ATP. Activity measurements of HXKs modified by site-directed mutagenesis suggest that the lack of catalytic activities in the HKL proteins might be attributed to any of numerous existing changes. Sliding windows analyses of coding sequences in A. thaliana and A. lyrata ssp. lyrata revealed a differential accumulation of nonsynonymous changes within exon 8 of both HKL1 and HXK3 orthologs. We further discuss the possibility that the non-catalytic HKL proteins have regulatory functions instead of catalytic functions.

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Sir-dependent downregulation of various aging processes

Cited by 10 publications

References 59 publications

Function of Arabidopsis hexokinase-like1 as a negative regulator of plant growth

Function of Arabidopsis hexokinase-like1 as a negative regulator of plant growth

Characterization of regulatory non-catalytic hexokinases in Aspergillus nidulans

Expression and evolutionary features of the hexokinase gene family in Arabidopsis

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