Furthermore, its activity is regulated by SnRK1, which adds phosphates to three specific locations on the protein. The experiments show that bZIP63 is involved in controlling responses to starvation. studied the role of a bZIP protein called bZIP63 during starvation in the plant Arabidopsis. Two bZIP proteins work together to switch on a gene, and the combination of bZIP proteins that interact can influence which genes are switched on. It has been suggested that a group of transcription factors called the bZIP proteins may be regulated by SnRK1. SnRK1 has ‘kinase’ activity, that is, it can alter the activities of other proteins by adding small molecules called phosphates to them. To perform the second job, SnRK1 is thought to control the activity of proteins called transcription factors-which alter the expression of genes by binding to DNA-but it is not known which ones. In plants, an enzyme called SnRK1 plays a crucial role in responses to starvation in two ways: by altering the activities of enzymes involved in metabolism and by regulating the expression of genes. Organisms need to adjust their metabolism in response to changing environmental conditions to ensure that they balance their energy intake with the demands of growth and reproduction. A bzip63 knock-out mutant exhibited starvation-related phenotypes, which could be functionally complemented by wild type bZIP63, but not by a version harboring point mutations in the identified SnRK1 target sites. Phosphorylation of bZIP63 by SnRK1 changed its dimerization preference, thereby affecting target gene expression and ultimately primary metabolism. Here we identified the Arabidopsis transcription factor bZIP63 as key regulator of the starvation response and direct target of the SnRK1 kinase. While the first part is well established, the latter function is only partially understood in animals and not at all in plants. They act at two different levels: by modulating the activity of key metabolic enzymes, and by massive transcriptional reprogramming. The evolutionary conserved AMPK/Snf1/SnRK1 kinases are well-known metabolic master regulators in the low-energy response in animals, yeast and plants. Metabolic adjustment to changing environmental conditions, particularly balancing of growth and defense responses, is crucial for all organisms to survive.
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