Molecular Characterization of Arabidopsis thaliana Snf1-Related Kinase 1

Plants have molecular mechanisms for nutrient-related stress responses; however, their exact regulation remains unclear. For example, the integral myo-inositol (inositol) signal transduction pathway allows Arabidopsis thaliana to sense and respond to changes in environmental stimuli, such as water, light availability, and nutrient stress. The inositol signaling pathway relies on dynamic changes in second messenger levels of inositol(1,4,5)P3 (InsP3) and is regulated by myo-inositol polyphosphate 5-phosphatases (5PTases). The 5PTses keep balance between InsP3 signal transduction and termination. Previous work has identified the Sucrose non-fermenting (Snf) 1-related kinase (SnRK1.1) as a binding partner to 5PTase13, a potential InsP3 regulator, and a novel protein called P80, a predicted component of the Cullin4 (CUL4) E3 Ubiquitin ligase complex. In plants, SnRK1.1 is a central integrator of metabolism, stress responses, and developmental signals. Moreover, SnRK1.1 is conserved with the eukaryotic AMP-activated protein (AMPK) and Snf1 kinases—enzymes fundamental to transcriptional regulation and metabolic balance. Studying SnRK1.1 regulation may reveal mechanisms for agricultural sustainability and may offer valuable links to understanding metabolic diseases and lifespan in humans.

Therefore, the research presented here centered on characterizing the regulation of SnRK1 gene expression and steady-state protein levels in plants. I show developmental and nutrient-related regulation of spatial expression patterns of SnRK1 genes and SnRK1.1 protein. Further, I present a model for regulation of SnRK1.1 protein stability in vivo based on SnRK1.1 steady-state protein levels in p80 and cul4 co-suppressed (cs) mutants. My results indicate SnRK1.1 regulation is dynamic, and dependent on the timing of particular cues from development and the environment.