In plants, sensing the levels of external and internal nutrients is essential for reprogramming the transcriptome and adapting to the fluctuating environment. Phosphate (Pi) is a key plant nutrient, and a large proportion of Pi starvation-responsive genes are under the control of PHOSPHATE STARVATION RESPONSE REGULATOR 1 (PHR1) in Arabidopsis (AtPHR1) and its homologs, such as Oryza sativa (Os)PHR2 in rice. AtPHR1 and OsPHR2 expression is not very responsive to Pi starvation, raising the question as to how plants sense changes in cellular Pi levels to activate the central regulator. SPX [named after SYG1 (suppressor of yeast gpa1), Pho81 (CDK inhibitor in yeast PHO pathway), and XPR1 (xenotropic and polytropic retrovirus receptor)] proteins that harbor only the SPX domain are reported to be involved in the negative regulation of Pi starvation responses. Here, we show that the nuclear localized SPX proteins SPX1 and SPX2 are Pi-dependent inhibitors of the activity of OsPHR2 in rice. Indeed, SPX1 and SPX2 proteins interact with PHR2 through their SPX domain, inhibiting its binding to P1BS (the PHR1-binding sequence: GNATATNC). In vivo data, as well as results from in vitro experiments using purified SPX1, SPX2, and OsPHR2 proteins, showed that SPX1 and SPX2 inhibition of OsPHR2 activity is Pi-dependent. These data provide evidence to support the involvement of SPX1 and SPX2 in the Pi-sensing mechanism in plants.SPX-domain protein | PHR2 | Pi signaling | Pi-dependent inhibition P hosphorus (P) is an essential macroelement for plant growth and development. Because of high chemical fixation, slow diffusion, and substantial fractions of organic compounds by microorganisms, phosphate (Pi) limitation is usually a constraint for crop production in cultivated soils (1). However, intensive application of P fertilizer to increase agricultural production results in higher cost and environmental pollution and aggravates the shortage of nonrenewable resources worldwide for P fertilizer production (2). Therefore, improving effective Pi use by crops to reduce agricultural dependence on heavy Pi fertilizer application is an important challenge for sustainable agricultural production.The role of Arabidopsis PHOSPHATE STARVATION RESPONSE REGULATOR 1 (AtPHR1) and its orthologs as important regulators in Pi signaling and homeostasis through binding to the PHR1-binding sequence (P1BS) is well established in plants. AtPHR1 binds as a dimer to an imperfect palindromic sequence (GNATATNC), and this DNA-binding ability is dependent on the MYB and coiled-coil (CC) domains present in AtPHR1 and related proteins (3, 4). Orthologs of AtPHR1 have also been described in rice [Oryza sativa ( The SPX domain (Pfam PF03105) is named after the suppressor of yeast gpa1 (SYG1), the yeast cyclin-dependent kinase inhibitor (PHO81), and the human xenotropic and polytropic retrovirus receptor 1 (XPR1). In yeast (Saccharomyces cerevisiae), the SPX domain forms part of the competitive dual-transporter system that prolongs preparation for starvation and faci...

The Golgi apparatus controls the formation of non-centrosomal microtubule arrays important for Golgi organization, polarized transport, cell motility, and cell differentiation. Here, we show that CAMSAP2 stabilizes and attaches microtubule minus ends to the Golgi through a complex of AKAP450 and myomegalin. CLASPs stabilize CAMSAP2-decorated microtubules but are not required for their Golgi tethering. AKAP450 is also essential for Golgi microtubule nucleation, and myomegalin and CDK5RAP2 but not CAMSAP2 contribute to this function. In the absence of centrosomes, AKAP450- and CAMSAP2-dependent pathways of microtubule minus-end organization become dominant, and the presence of at least one of them is needed to maintain microtubule density. Strikingly, a compact Golgi can be assembled in the absence of both centrosomal and Golgi microtubules. However, CAMSAP2- and AKAP450-dependent Golgi microtubules facilitate Golgi reorientation and cell invasion in a 3D matrix. We propose that Golgi-anchored microtubules are important for polarized cell movement but not for coalescence of Golgi membranes.

Meiosis is key to sexual reproduction and genetic diversity. Here, we show that the Arabidopsis cyclin‐dependent kinase Cdk1/Cdk2 homolog CDKA;1 is an important regulator of meiosis needed for several aspects of meiosis such as chromosome synapsis. We identify the chromosome axis protein ASYNAPTIC 1 (ASY1), the Arabidopsis homolog of Hop1 (homolog pairing 1), essential for synaptonemal complex formation, as a target of CDKA;1. The phosphorylation of ASY1 is required for its recruitment to the chromosome axis via ASYNAPTIC 3 (ASY3), the Arabidopsis reductional division 1 (Red1) homolog, counteracting the disassembly activity of the AAA+ ATPase PACHYTENE CHECKPOINT 2 (PCH2). Furthermore, we have identified the closure motif in ASY1, typical for HORMA domain proteins, and provide evidence that the phosphorylation of ASY1 regulates the putative self‐polymerization of ASY1 along the chromosome axis. Hence, the phosphorylation of ASY1 by CDKA;1 appears to be a two‐pronged mechanism to initiate chromosome axis formation in meiosis.

The important anticancer drug Taxol ® (paclitaxel, PTX) owes its unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. The conformation of the microtubule-bound drug has been the focus of numerous research efforts, since the inability of polymerized tubulin to form crystals precludes structure proof by X-ray crystallography. Likewise, although the αβ-tubulin dimer structure has been solved by electron crystallography, the 3.7 Å resolution is too low to permit direct determination of either ligand conformation or binding pose. In this study we present experimental results from 2 H{ 19 F} REDOR NMR that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.

The important anticancer drug paclitaxel binds to the -subunit of the R -tubulin dimer in the microtubule in a stoichiometric ratio, promoting microtubule polymerization and stability. The conformation of microtubule-bound drug has been the subject of intense study, and various suggestions have been proposed. In previous work we presented experimental and theoretical evidence that paclitaxel adopts a T-shaped conformation when it is bound to tubulin. In this study we report additional experimental data and calculations that delineate the allowable parameters for effective paclitaxel-tubulin interactions.

Epigallocatechin gallate (EGCG) from green tea can induce apoptosis in cancerous cells, but the underlying molecular mechanisms remain poorly understood. Using SPR and NMR, here we report a direct, μM interaction between EGCG and the tumor suppressor p53 (KD = 1.6 ± 1.4 μM), with the disordered N-terminal domain (NTD) identified as the major binding site (KD = 4 ± 2 μM). Large scale atomistic simulations (>100 μs), SAXS and AUC demonstrate that EGCG-NTD interaction is dynamic and EGCG causes the emergence of a subpopulation of compact bound conformations. The EGCG-p53 interaction disrupts p53 interaction with its regulatory E3 ligase MDM2 and inhibits ubiquitination of p53 by MDM2 in an in vitro ubiquitination assay, likely stabilizing p53 for anti-tumor activity. Our work provides insights into the mechanisms for EGCG’s anticancer activity and identifies p53 NTD as a target for cancer drug discovery through dynamic interactions with small molecules.

End-binding proteins regulate the dynamics and function of microtubule plus ends by recruiting a plethora of diverse factors. Yang et al. show that EB1 and EB3 also affect microtubule minus ends by participating in their attachment to Golgi membranes. This function is important for cell polarity and migration.

Feedback-Driven Assembly of the Axon Initial Segment Highlights d Ankyrin-G in complex with EBs recruits microtubule bundles to the plasma membrane d TRIM46 is a rescue factor that forms stable parallel microtubule bundles d TRIM46-bound microtubules direct Neurofascin-186 trafficking to the proximal axon d Ankyrin-G controls Neurofascin-186 retention in the axon initial segment