Role of the Arabidopsis Glucose Sensor HXK1 in Nutrient, Light, and Hormonal Signaling

Abstract

Glucose modulates many vital processes in photosynthetic plants. Analyses of Arabidopsis glucose insensitive2 (gin2) mutants define the physiological functions of a specific hexokinase (HXK1) in the plant glucose-signaling network. HXK1 coordinates intrinsic signals with extrinsic light intensity. HXK1 mutants lacking catalytic activity still support various signaling functions in gene expression, cell proliferation, root and inflorescence growth, and leaf expansion and senescence, thus demonstrating the uncoupling of glucose signaling from glucose metabolism. The gin2 mutants are also insensitive to auxin and hypersensitive to cytokinin. Plants use HXK as a glucose sensor to interrelate nutrient, light, and hormone signaling networks for controlling growth and development in response to the changing environment.

Sugar-based growth, astaxanthin accumulation and carotenogenic transcription of heterotrophic Chlorella zofingiensis (Chlorophyta)

“…PCC 6803 [23]. The glucose effects on the expression of genes are suggested to result from the glucosesensing and signaling with the hexokinase as the key sensor in a variety of yeasts, mammals and higher plants [24][25][26][27], or from changes in the cytosolic redox state or electron flow of respiratory electron transport [24,28,29]. A correlation between biomass, astaxanthin production, and the transcripts of BKT and CHYb genes was evident in the cells treated with the sugars.…”

Partial purification of tightly bound mitochondrial hexokinase from maize (Zea mays L.) root membranes

“…However, glucose-insensitive and glucose-oversensitive mutants have revealed extensive and intimate connections between glucose and plant hormone signaling pathways such as ethylene and abscisic acid (18,19). Accordingly, in Arabidopsis thaliana, AtHK 1 activity is found associated with mitochondria, similarly to the NC-HK activity found in maize (Zea mays) or rice (Oryza sativa) roots that also exhibit the sugar sensing response (14)(15)(16)18,19). The HK sensing function may depend on its subcellular localization, translocation and/or interactions with downstream effectors, but these properties are still unknown.…”

Sugar-induced plant growth is dependent on brassinosteroids

“…However, whether the mechanisms for sugar promotion of plant growth in shade are identical to that in darkness remain to be determined. Moore et al (2003) reported that when the Arabidopsis gin2-1 mutant (a null mutant of HXK1) was grown under a shade condition, it showed defects in hypocotyl elongation compared to its wild-type Ler, 7 indicating that HXK1 might play a role during shade promotion of plant growth.…”

“…5 Discovery of unique and global repression of photosynthetic genes by Glc in Arabidopsis led to identification of HXK1 as the first plant Glc sensor, which mediates Glc repression or promotion of gene transcription and plant growth. 6,7 Later on, diverse isoforms of HXK and HXK-like (HXL) genes were found in the genomes of many plants, including rice, maize, tomato, tobacco and Arabidopsis, which suggests that plants have evolved a complex mode of Glc signaling to support various growth strategies and architectures dictated by sugar availability. 4,7 Suc is the major transport sugar in higher plants and could also initiate signaling pathways leading to changes of gene expression and physiological adaptation, but a Suc sensor has not be identified.…”

“…6,7 Later on, diverse isoforms of HXK and HXK-like (HXL) genes were found in the genomes of many plants, including rice, maize, tomato, tobacco and Arabidopsis, which suggests that plants have evolved a complex mode of Glc signaling to support various growth strategies and architectures dictated by sugar availability. 4,7 Suc is the major transport sugar in higher plants and could also initiate signaling pathways leading to changes of gene expression and physiological adaptation, but a Suc sensor has not be identified. 8 Brassinosteroids (BRs) are a class of polyhydroxylated sterol derivatives that regulate diverse developmental and physiological processes, including seed germination, seedling photomorphogenesis, stomata differentiation, organ boundary formation, flowering, male fertility, and even responses to biotic and abiotic stresses.…”