Abstract
In plants, SNF1-related kinase (SnRK1) responds to the availability of carbohydrates as well as to environmental stresses by down-regulating ATP consuming biosynthetic processes, while stimulating energy-generating catabolic reactions through gene expression and post-transcriptional regulation. The functional SnRK1 complex is a heterotrimer where the catalytic α subunit associates with a regulatory β subunit and an activating γ subunit. Several different metabolites as well as the hormone abscisic acid (ABA) have been shown to modulate SnRK1 activity in a cell- and stimulus-type specific manner. It has been proposed that tissue- or stimulus-specific expression of adapter proteins mediating SnRK1 regulation can at least partly explain the differences observed in SnRK1 signaling. By using yeast two-hybrid and in planta bi-molecular fluorescence complementation assays we were able to demonstrate that proteins containing the domain of unknown function (DUF) 581 could interact with both isoforms of the SnRK1α subunit (AKIN10/11) of Arabidopsis. A structure/function analysis suggests that the DUF581 is a generic SnRK1 interaction module and co-expression with DUF581 proteins in plant cells leads to reallocation of the kinase to specific regions within the nucleus. Yeast two-hybrid analyses suggest that SnRK1 and DUF581 proteins share common interaction partners inside the nucleus. The analysis of available microarray data implies that expression of the 19 members of the DUF581 encoding gene family in Arabidopsis is differentially regulated by hormones and environmental cues, indicating specialized functions of individual family members. We hypothesize that DUF581 proteins could act as mediators conferring tissue- and stimulus-type specific differences in SnRK1 regulation.
Highlights
The maintenance of cellular energy homeostasis in response to fluctuating internal and external conditions is vital for all living organisms
SNF1-related protein kinase 1 (SnRK1) protein kinases are considered central regulators of energy and stress signaling in plants
We could show that majority of Arabidopsis proteins containing DUF581 can interact with SnRK1.1/AKIN10 and SnRK1.2/AKIN11 in yeast and in planta
Summary
The maintenance of cellular energy homeostasis in response to fluctuating internal and external conditions is vital for all living organisms. An evolutionarily conserved protein kinase known as AMP-activated protein kinase (AMPK) in animals, sucrose non-fermenting kinase 1 (SNF1) in yeast, and SNF1-related protein kinase 1 (SnRK1) in plants integrates environmental stress signals, nutrient availability and energy depletion into adaptational responses (Hardie, 2007; Halford and Hey, 2009; Ghillebert et al, 2011). These include down-regulation of ATP-consuming processes and induction of energy-generating catabolic reactions through post-translational modification of key metabolic enzymes as well as large-scale transcriptional reprogramming (Baena-González et al, 2007; Baena-González and Sheen, 2008).
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