Nuclear speckle integrity and function require TAO2 kinase

Regulation of plant resistance to salt stress by the SnRK1-dependent splicing factor SRRM1L

Most splicing factors are extensively phosphorylated but their physiological functions in plant salt resistance are still elusive. We found that phosphorylation by SnRK1 kinase is essential for SRRM1L nuclear speckle formation and its splicing factor activity in plant cells. In Arabidopsis, loss-of-function of SRRM1L leads to the occurrence of alternative pre-mRNA splicing events and compromises plant resistance to salt stress. In Arabidopsis srrm1l mutant line, we identified an intron-retention Nuclear factor Y subunit A 10 (NFYA10) mRNA variant by RNA-Seq and found phosphorylation-dependent RNA-binding of SRRM1L is indispensable for its alternative splicing activity. In the wild-type Arabidopsis, salt stress can activate SnRK1 to phosphorylate SRRM1L, triggering enrichment of functional NFYA10.1 variant to enhance plant salt resistance. By contrast, the Arabidopsis srrm1l mutant accumulates nonfunctional NFYA10.3 variant, sensitizing plants to salt stress. In summary, this work deciphered the molecular mechanisms and physiological functions of SnRK1-SRRM1L-NFYA10 module, shedding light on a regulatory pathway to fine-tune plant adaptation to abiotic stress at the post-transcriptional and post-translational levels.

Inhibition of mRNA nuclear export promotes SARS-CoV-2 pathogenesis

The nonstructural protein 1 (Nsp1) of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is a virulence factor that targets multiple cellular pathways to inhibit host gene expression and antiviral response. However, the underlying mechanisms of the various Nsp1-mediated functions and their contributions to SARS-CoV-2 virulence remain unclear. Among the targets of Nsp1 is the mRNA (messenger ribonucleic acid) export receptor NXF1-NXT1, which mediates nuclear export of mRNAs from the nucleus to the cytoplasm. Based on Nsp1 crystal structure, we generated mutants on Nsp1 surfaces and identified an acidic N-terminal patch that is critical for interaction with NXF1-NXT1. Photoactivatable Nsp1 probe reveals the RNA Recognition Motif (RRM) domain of NXF1 as an Nsp1 N-terminal binding site. By mutating the Nsp1 N-terminal acidic patch, we identified a separation-of-function mutant of Nsp1 that retains its translation inhibitory function but substantially loses its interaction with NXF1 and reverts Nsp1-mediated mRNA export inhibition. We then generated a recombinant (r)SARS-CoV-2 mutant on the Nsp1 N-terminal acidic patch and found that this surface is key to promote NXF1 binding and inhibition of host mRNA nuclear export, viral replication, and pathogenicity in vivo. Thus, these findings provide a mechanistic understanding of Nsp1-mediated mRNA export inhibition and establish the importance of this pathway in the virulence of SARS-CoV-2.

Pleiotropic functions of TAO kinases and their dysregulation in neurological disorders

Thousand and one amino acid kinases (TAOKs) are relatively understudied and functionally pleiotropic protein kinases that have emerged as important regulators of neurodevelopment. Through their conserved amino-terminal catalytic domain, TAOKs mediate phosphorylation at serine/threonine residues in their substrates, but it is their divergent regulatory carboxyl-terminal domains that confer both exquisite functional specification and cellular localization. In this Review, we discuss the physiological roles of TAOKs and the intricate signaling pathways, molecular interactions, and cellular behaviors they modulate-from cell stress responses, division, and motility to tissue homeostasis, immunity, and neurodevelopment. These insights are then integrated into an analysis of the known and potential impacts of disease-associated variants of TAOKs, with a focus on neurodevelopmental disorders, pain and addiction, and neurodegenerative diseases. Translating this foundation into clinical benefits for patients will require greater structural and functional differentiation of the TAOKs afforded by their individually specialized domains.