We investigated the role of the mRNA decay factor Protein Associated with Topoisomerase II (PAT1) by generating multiple mutants of pat1 and its homologs, path1 and path2. Through detailed analysis of their developmental phenotypes and RNA sequencing, we concluded that PAT1 plays a crucial role in leaf patterning. Moreover, it operates in conjunction with the other two PATs redundantly throughout plant development.

Evolutionarily conserved protein associated with topoisomerase II (PAT1) proteins activate mRNA decay through binding mRNA and recruiting decapping factors to optimize posttranscriptional reprogramming. Here, we generated multiple mutants of pat1, pat1 homolog 1 (path1), and pat1 homolog 2 (path2) and discovered that pat triple mutants exhibit extremely stunted growth and all mutants with pat1 exhibit leaf serration while mutants with pat1 and path1 display short petioles. All three PATs can be found localized to processing bodies and all PATs can target ASYMMETRIC LEAVES 2-LIKE 9 transcripts for decay to finely regulate apical hook and lateral root development. In conclusion, PATs exhibit both specific and redundant functions during different plant growth stages and our observations underpin the selective regulation of the mRNA decay machinery for proper development.

When bound to toxic or non-toxic ligands, aryl hydrocarbon receptors (AhRs) are activated and nuclear translocation occurs; AhRs are bound to molecular chaperone complexes, AhR-HSP90-XAP2-p23 for toxic ligands, whereas for non-toxic ligands AhR-HSP90- XAP2 for non-toxic ligands. Toxic and non-toxic ligand selectivity of AhR depends on the components of the molecular chaperone complex.

The aryl hydrocarbon receptor (AhR) forms a complex with the HSP90-XAP2-p23 molecular chaperone when the cells are exposed to toxic compounds. Recently, 1,4-dihydroxy-2-naphthoic acid (DHNA) was reported to be an AhR ligand. Here, we investigated the components of the molecular chaperone complex when DHNA binds to AhR. Proteins eluted from the 3-Methylcolanthrene-affinity column were AhR-HSP90-XAP2-p23 complex. The AhR-molecular chaperone complex did not contain p23 in the eluents from the DHNA-affinity column. In 3-MC-treated cells, AhR formed a complex with HSP90-XAP2-p23 and nuclear translocation occurred within 30 min, while in DHNA-treated cells, AhR formed a complex with AhR-HSP90-XAP2, and translocation was slow from 60 min. Thus, the AhR activation mechanism may differ when DHNA is the ligand compared to toxic ligands.

Contrary to previous predictions, we provide evidence that the small GTPase κB-Ras possesses intrinsic hydrolytic activity. However, low nucleotide affinity leads to fast nucleotide exchange and renders κB-Ras constitutively GTP-bound in cells. We characterize κB-Ras mutations occurring in tumors and define that nucleotide binding supports protein stability but is not required for a constitutive noneffector interaction with RalGAP complexes.

κB-Ras (NF-κB inhibitor-interacting Ras-like protein) GTPases are small Ras-like GTPases but harbor interesting differences in important sequence motifs. They act in a tumor-suppressive manner as negative regulators of Ral (Ras-like) GTPase and NF-κB signaling, but little is known about their mode of function. Here, we demonstrate that, in contrast to predictions based on primary structure, κB-Ras GTPases possess hydrolytic activity. Combined with low nucleotide affinity, this renders them fast-cycling GTPases that are predominantly GTP-bound in cells. We characterize the impact of κB-Ras mutations occurring in tumors and demonstrate that nucleotide binding affects κB-Ras stability but is not strictly required for RalGAP (Ral GTPase-activating protein) binding. This demonstrates that κB-Ras control of RalGAP/Ral signaling occurs in a nucleotide-binding- and switch-independent fashion.