The plant hormone ethylene regulates a wide range of developmental processes and the response of plants to stress and pathogens. Genetic studies in Arabidopsis led to a partial elucidation of the mechanisms of ethylene action. Ethylene signal transduction initiates with ethylene binding at a family of ethylene receptors and terminates in a transcription cascade involving the EIN3/EIL and ERF families of plant-specific transcription factors. Here, we identify two Arabidopsis F box proteins called EBF1 and EBF2 that interact physically with EIN3/EIL transcription factors. EBF1 overexpression results in plants insensitive to ethylene. In contrast, plants carrying the ebf1 and ebf2 mutations display a constitutive ethylene response and accumulate the EIN3 protein in the absence of the hormone. Our work places EBF1 and EBF2 within the genetic framework of the ethylene-response pathway and supports a model in which ethylene action depends on EIN3 protein stabilization.
Spindle alignment is the process in which the two spindle poles are directed toward preselected and opposite cell ends. In budding yeast, the APC-related molecule Kar9 is required for proper alignment of the spindle with the mother-bud axis. We find that Kar9 localizes to the prospective daughter cell spindle pole. Kar9 is transferred from the pole to cytoplasmic microtubules, which are then guided in a myosin-dependent manner to the bud. Clb4/Cdc28 kinase phosphorylates Kar9 and accumulates on the pole destined to the mother cell. Mutations that block phosphorylation at Cdc28 consensus sites result in localization of Kar9 to both poles and target them both to the bud. Thus, Clb4/Cdc28 prevents Kar9 loading on the mother bound pole. In turn, asymmetric distribution of Kar9 ensures that only one pole orients toward the bud. Our results indicate that Cdk1-dependent spindle asymmetry ensures proper alignment of the mitotic spindle with the cell division axis.
Yeast Las17 protein is homologous to the Wiskott-Aldrich Syndrome protein, which is implicated in severe immunodeficiency. Las17p/Bee1p has been shown to be important for actin patch assembly and actin polymerization. Here we show that Las17p interacts with the Arp2/3 complex. LAS17 is an allele-specific multicopy suppressor of ARP2 and ARP3 mutations; overexpression restores both actin patch organization and endocytosis defects in ARP2 temperature-sensitive (ts) cells. Six of seven ARP2 ts mutants and at least one ARP3 ts mutant are synthetically lethal with las17Delta ts confirming functional interaction with the Arp2/3 complex. Further characterization of las17Delta cells showed that receptor-mediated internalization of alpha factor by the Ste2 receptor is severely defective. The polarity of normal bipolar bud site selection is lost. Las17-gfp remains localized in cortical patches in vivo independently of polymerized actin and is required for the polarized localization of Arp2/3 as well as actin. Coimmunoprecipitation of Arp2p with Las17p indicates that Las17p interacts directly with the complex. Two hybrid results also suggest that Las17p interacts with actin, verprolin, Rvs167p and several other proteins including Src homology 3 (SH3) domain proteins, suggesting that Las17p may integrate signals from different regulatory cascades destined for the Arp2/3p complex and the actin cytoskeleton.
We used live imaging and EM to study migration of multiple nuclei in A. gossypii. Three types of nuclear movements, oscillation, rotation, and bypassing, depend on cytoplasmic microtubules while a fourth type, co-transport with the cytoplasmic stream, does not. Nuclear MTOCs emanating perpendicular and tangential cMTs lead cMT-dependent movements
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.