Lavy, M. | Search bioRxiv

bioRxiv2023

Comparative mutant analyses reveal a novel mechanism of ARF regulation in land plants

A major challenge in plant biology is to understand how the plant hormone auxin regulates diverse transcriptional responses throughout development, in different environments, and in different species. The answer may lie in the specific complement of auxin signaling components in each cell. The balance between activators (class-A AUXIN RESPONSE FACTORS) and repressors (class-B ARFs) is particularly important. It is unclear how this balance is achieved. Through comparative analysis of novel, dominant mutants in maize and the moss Physcomitrium patens, we have discovered a [~]500-million-year-old mechanism of class-B ARF protein level regulation, important in determining cell fate decisions across land plants. Thus, our results add a key piece to the puzzle of how auxin regulates plant development.

plant biology↗

bioRxiv2020

Molecular and functional diversity of distinct subpopulations of extracellular vesicles from stressed pancreatic beta cells: implications for autoimmunity

Beta cell failure and apoptosis following islet inflammation have been associated with autoimmune type 1 diabetes pathogenesis. As conveyors of biological active material, extracellular vesicles (EV) act as mediators in communication with immune effectors fostering the idea that EV from inflamed beta cells may contribute to autoimmunity. Evidence accumulates that beta exosomes promote diabetogenic responses, but relative contributions of larger vesicles as well as variations in the composition of the beta cells vesiculome due to environmental changes have not been explored yet. Here, we made side-by-side comparisons of the phenotype and function of apoptotic bodies (AB), microvesicles (MV) and small EV (sEV) isolated from an equal amount of MIN6 beta cells exposed to inflammatory, hypoxic or genotoxic stressors. Under normal conditions, large vesicles represent 93% of the volume, but only 2% of the number of the vesicles. Our data reveal a consistently higher release of AB and sEV and to a lesser extent of MV, exclusively under inflammatory conditions commensurate with a 4-fold increase in the total volume of the vesiculome and enhanced export of immune-stimulatory material including the autoantigen insulin, microRNA, and cytokines. Whilst inflammation does not change the concentration of insulin inside the EV, specific Toll-like receptor-binding microRNA sequences preferentially partition into sEV. Exposure to inflammatory stress engenders drastic increases in the expression of monocyte chemoattractant protein 1 in all EV and of interleukin-27 solely in AB suggesting selective sorting towards EV subspecies. Functional in vitro assays in mouse dendritic cells and macrophages reveal further differences in the aptitude of EV to modulate expression of cytokines and maturation markers. These findings highlight the different quantitative and qualitative imprints of environmental changes in subpopulations of beta EV that may contribute to the spread of inflammation and sustained immune cell recruitment at the inception of the (auto-) immune response. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=194 SRC="FIGDIR/small/003145v1_ufig1.gif" ALT="Figure 1"> View larger version (62K): org.highwire.dtl.DTLVardef@1bf7c79org.highwire.dtl.DTLVardef@85098dorg.highwire.dtl.DTLVardef@362e33org.highwire.dtl.DTLVardef@11349ab_HPS_FORMAT_FIGEXP M_FIG C_FIG Inflammation stimulates release of a heterogeneous population of beta EV with differential expression of immunogenic substances involved in immune cell recruitment and activation. HighlightsO_LIStress engenders an up to four-fold increase in the volume of the vesiculome and enhanced auto-antigen release C_LIO_LICytokines are selectively sorted into EV subspecies C_LIO_LITLR-binding microRNAs are enriched in sEV C_LIO_LIEV from stressed beta cells promote dendritic and macrophage cell activation C_LI

immunology↗

bioRxiv2018

The Ca2+ sensor protein CMI1 fine tunes root development, auxin distribution and responses

Signaling cross-talks between auxin, a regulator of plant development and Ca2+, a universal second messenger have been proposed to modulate developmental plasticity in plants. However, the underlying molecular mechanisms are largely unknown. Here we report that in Arabidopsis roots, auxin elicits specific Ca2+ signaling pattern that spatially coincide with the expression pattern of auxin-regulated genes. We identified the EF-hand protein CMI1 (Ca2+ sensor Modulator of ICR1) as an interactor of the ROP effector ICR1 (Interactor of Constitutively active ROP). CMI1 is monomeric in solution, changes its secondary structure at Ca2+ concentrations ranging from 10-9 to 10-8 M and its interaction with ICR1 is Ca2+ dependent, involving a conserved hydrophobic pocket. cmi1 mutants display an increased auxin response including shorter primary roots, longer root hairs, longer hypocotyls and altered lateral root formation while ectopic expression of CMI1 induces root growth arrest and reduced auxin responses at the root tip. When expressed alone, CMI1 is localized at the plasma membrane, the cytoplasm and in nuclei. Interaction of CMI1 and ICR1 results in exclusion of CMI1 from nuclei and suppression of the root growth arrest. CMI1 expression is directly upregulated by auxin while expression of auxin induced genes is enhanced in cmi1 concomitantly with repression of auxin induced Ca2+ increases in the lateral root cap and vasculature, indicating that CMI1 represses early auxin responses. Collectively, our findings identify a crucial function of Ca2+ signaling and CMI1 in root growth and suggest an auxin-Ca2+ regulatory feedback loop that fine tunes root development.

plant biology↗