Mutations of the Atyak1 Kinase Suppress Tor Deficiency in Arabidopsis

The Target Of Rapamycin (TOR) kinase is a conserved energy sensor that regulates growth in response to environmental cues. However, little is known about TOR pathway regulatory elements or substrates in plants. We used Arabidopsis mutants affected in the LST8 gene, a core element of the TOR complex, to search for suppressors of lst8-1-1 (sol) mutants. Two sol lines were isolated, both with mutations in the AtYAK1 gene, which is a member of the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family. Atyak1 mutations improved growth and partly rescued the developmental defects observed in lst8-1-1 mutants. They also conferred resistance to AZD-8055, a specific TOR inhibitor. Moreover, atyak1 mutations suppressed the transcriptomic and metabolic perturbations, as well as the ABA hypersensitivity of the lst8-1-1 mutants. Thus, our findings reveal that AtYAK1 is a negative regulatory element of the TOR signaling pathway, which needs to be switched off to activate plant growth.