Snf1‐related protein kinase 1 is needed for growth in a normal day–night light cycle

The yeast Snf1 protein kinase and its animal homologue, the AMP‐activated protein kinase, play important roles in metabolic regulation, by serving as energy gauges that turn off energy‐consuming processes and mobilize energy reserves during low‐energy conditions. The closest homologue of these kinases in plants is Snf1‐related protein kinase 1 (SnRK1). We have cloned two SnRK1‐encoding genes, PpSNF1a and PpSNF1b , in the moss Physcomitrella patens , where gene function can be studied directly by gene targeting in the haploid gametophyte. A snf1a snf1b double knockout mutant is viable, but lacks all Snf1‐like protein kinase activity. The mutant has a complex phenotype that includes developmental abnormalities, premature senescence and altered sensitivities to plant hormones. Remarkably, the double knockout mutant also requires continuous light, and is unable to grow in a normal day–night light cycle. This suggests that SnRK1 is needed for metabolic changes that help the plant cope with the dark hours of the night.