A phyB-PIF1-SPA1 kinase regulatory complex promotes photomorphogenesis in Arabidopsis (OA) (Nature Communications)

CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) is one of the best characterized E3 ubiquitin ligases with broad roles as a central repressor of light signaling in plants to cancer biology in mammals. In plants, COP1 interacts with SUPPRESSOR OF PHYA-105 1 family members (SPA1-SPA4) and forms a stable COP1/SPA complex. Paik et al., provide evidence that SPA1, a component of the COP1-SPA E3 ubiquitin ligase complex, itself can act as a protein kinase. By performing extensive biochemical, genetic and genomic analyses, they provide strong evidence that SPA1 is a bona fide Serine/Threonine kinase that is necessary for the light-induced phosphorylation and degradation of PIF1. They also provide mechanistic details on how the red/far-red light photoreceptor phytochrome B directly interacts with SPA1 kinase in response to red light, and this interaction plays a pivotal role in inducing PIF1 phosphorylation and subsequent degradation to promote seed germination and seedling development. This is a ground-breaking work discovering a novel kinase that might serve as a model for other kinase-E3 ubiquitin ligase complexes (e.g., mammalian COP1-Trib kinase complex) and help decipher new intriguing roles of COP1 and associated kinases from other systems. (Summary by Inyup Paik) Nature Communications: 10.1038/s41467-019-12110-y