Abstract
Glucose modulates plant metabolism, growth, and development. In Arabidopsis (Arabidopsis thaliana), Hexokinase1 (HXK1) is a glucose sensor that may trigger abscisic acid (ABA) synthesis and sensitivity to mediate glucose-induced inhibition of seedling development. Here, we show that the intensity of short-term responses to glucose can vary with ABA activity. We report that the transient (2 h/4 h) repression by 2% glucose of AtbZIP63, a gene encoding a basic-leucine zipper (bZIP) transcription factor partially involved in the Snf1-related kinase KIN10-induced responses to energy limitation, is independent of HXK1 and is not mediated by changes in ABA levels. However, high-concentration (6%) glucose-mediated repression appears to be modulated by ABA, since full repression of AtbZIP63 requires a functional ABA biosynthetic pathway. Furthermore, the combination of glucose and ABA was able to trigger a synergistic repression of AtbZIP63 and its homologue AtbZIP3, revealing a shared regulatory feature consisting of the modulation of glucose sensitivity by ABA. The synergistic regulation of AtbZIP63 was not reproduced by an AtbZIP63 promoter-5'-untranslated region::β-glucuronidase fusion, thus suggesting possible posttranscriptional control. A transcriptional inhibition assay with cordycepin provided further evidence for the regulation of mRNA decay in response to glucose plus ABA. Overall, these results indicate that AtbZIP63 is an important node of the glucose-ABA interaction network. The mechanisms by which AtbZIP63 may participate in the fine-tuning of ABA-mediated abiotic stress responses according to sugar availability (i.e., energy status) are discussed.
Highlights
Glucose modulates plant metabolism, growth, and development
AtbZIP63 Is Repressed by Glc and abscisic acid (ABA), and Glc-Induced Repression Is Independent of HXK1 Glc Sensing Activity
To evaluate the short-term responses of C-group basic-leucine zipper (bZIP) genes AtbZIP9 (At5g24800), AtbZIP10 (At4g02640), AtbZIP25 (At3g54620), and AtbZIP63 (At5g28770) to Glc and ABA signals, wild-type Columbia (Col-0) seedlings grown for 6 d under constant dim light (20 mmol m22 s21) and in half-strength Murashige and Skoog (MS/2) liquid medium were treated for 4 h with 2% Glc or 100 mM ABA
Summary
Growth, and development. In Arabidopsis (Arabidopsis thaliana), Hexokinase (HXK1) is a glucose sensor that may trigger abscisic acid (ABA) synthesis and sensitivity to mediate glucose-induced inhibition of seedling development. A transcriptional inhibition assay with cordycepin provided further evidence for the regulation of mRNA decay in response to glucose plus ABA Overall, these results indicate that AtbZIP63 is an important node of the glucose-ABA interaction network. The mechanisms by which AtbZIP63 may participate in the finetuning of ABA-mediated abiotic stress responses according to sugar availability (i.e., energy status) are discussed To optimize their growth and development as sessile organisms, plants have developed a range of efficient mechanisms to sense and respond adequately to ever-changing environmental conditions. The characterization of glucose insensitive (gin2) mutants has provided compelling evidence for a Hexokinase (HXK1)-dependent Glc sensing and signaling pathway that is uncoupled from HXK phosphorylation activity and mediates the repression of photosynthetic gene expression and growth control in Arabidopsis (Moore et al, 2003). Complementation of the gin Arabidopsis mutant with rice (Oryza sativa) HXK5 and HXK6 indicates that HXK-mediated Glc sensing is conserved in angiosperms (Cho et al, 2009)
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