Biology subjects

Herger, A.

Publications and source records attributed to Herger, A..

5 recordsLinked to original sources

bioRxiv2025

The CATION CALCIUM EXCHANGER 4 (CCX4) regulates LRX1-related root hair development through Ca2+ homeostasis

Calcium, as a cellular second messenger, is essential for plant growth. A tip-focused Ca2+ gradient in polarized cells is considered to drive cell expansion. The cell wall polysaccharide pectin is a major Ca2+ binding structure and Ca2+ homeostasis is influenced by the cell wall architecture. LRR-extensin (LRX) proteins are extracellular regulators of cell wall development that are anchored in the cell wall by their extensin domain. The extensin-less LRX1{Delta}E14 variant of the root hair-expressed LRX1 of Arabidopsis induces a dominant-negative effect resulting in aberrant root hairs. In an effort to identify the underlying mechanism of the root hair defect caused by LRX1{Delta}E14, we isolated a suppressor of dominant-negative effect mutant, sune42. It codes for the CATION CALCIUM EXCHANGER 4 (CCX4) that localizes to the Golgi apparatus and was shown to have Ca2+ transport activity. A detailed investigation of the Ca2+ dynamics revealed that LRX1{Delta}E14 coincides with a defect in tip-focused cytoplasmic Ca2+ oscillation, and this effect is alleviated by the sune42 mutation. Additionally, reducing Ca2+ availability influences the LRX1{Delta}E14-induced root hair defect. We conclude that sune42 suppresses the root hair defect in LRX1{Delta}E14 through modulating cytoplasmic Ca2+ dynamics, pointing at the importance of the Golgi apparatus for cellular Ca2+ homeostasis.

plant biology↗

bioRxiv2024

A reference metagenome sequence of the lichen Cladonia rangiformis

[bullet] Lichens are an ancient symbiosis comprising the thalli of lichen-forming fungi, their photoautotrophic partners and their microbiome. So far, they were poorly studied at the genome sequence level. Here, we present a reference metagenome for the holobiont of Cladonia rangiformis. [bullet]Using long read sequences from an entire symbiotic complex, plus short read libraries from 28 additional diverse European lichen samples, we were able to separate genome sequences of 20 individual species. [bullet]We constructed chromosome-scale assemblies of the C. rangiformis fungus and its trebouxioid green algal photobiont Asterochloris mediterranea. The genome of the fungus comprises [~]22% transposable elements and is highly compartmentalized into genic regions and large TE-derived segments which show extensive signatures of repeat-induced point mutations (RIP). We found that A. mediterranea centromeres are predominantly derived from two interacting retrotransposon families. We also identified strong candidates for genes that were horizontally transferred from bacteria to both alga and fungus. Furthermore, we isolated 18 near-complete bacterial genomes, of which 13 are enriched in the lichen compared to surrounding soil. [bullet]Our study revealed that the thalli of C. rangiformis have a highly complex microbiome, comprising a mix of species that may include opportunists, ecologically obligate symbionts and possibly even lichen-beneficial bacteria.

evolutionary biology↗

bioRxiv2024

Histidine limitation causes alteration in the TOR network and plant development

Plant growth depends on growth regulators, nutrient availability, and amino acids levels. The TOR (Target of Rapamycin) network senses these parameters and influences cell wall formation and expansion accordingly. Cell wall integrity and structures are surveyed and modified by a complex array of cell wall integrity sensors, including LRR-extensins (LRXs), that function as hormone receptors and help to compact cell walls. Expressing the Arabidopsis root-hair specific LRX1 without the extensin domain, which anchors the protein to the cell wall, has a negative effect on root hair development. The mechanism of this negative effect was investigated by a suppressor screen, which led to the identification of a sune (suppressor of dominant-negative LRX1) mutant collection. The sune82 mutant was identified as an allele of HISN2 which encodes an enzyme essential for histidine biosynthesis. The sune82 mutation leads to reduced accumulation of histidine, and this influences the TOR network. The sune82 mutant reflects the impact of the TOR network on cell wall formation processes involving LRX proteins. It also represents an excellent tool to study the effects of reduced histidine levels on plant development, as it is a rare example of a viable partial loss-of-function allele in an essential biosynthetic pathway. HighlightPartial loss of function of HISN2 in sune82 results in a significant reduction in histidine content, which subsequently alters the TOR network.

cell biology↗

bioRxiv2023

Growth-inhibiting effects of the unconventional plant APYRASE 7 of Arabidopsis thaliana influences the LRX1/FER/RALF growth regulatory module

Plant cell growth involves coordination of numerous processes and signaling cascades among the different cellular compartments to concomitantly enlarge the protoplast and the surrounding cell wall. In Arabidopsis thaliana, the cell wall integrity-sensing process involves the extracellular LRX (LRR-Extensin) proteins that bind RALF (Rapid ALkalinization Factor) peptide hormones and, in vegetative tissues, interact with the transmembrane receptor kinase FERONIA (FER). This LRX/RALF/FER signaling module influences cell wall composition and regulates cell growth. The numerous proteins involved in or influenced by this module are beginning to be characterized. In a genetic screen, mutations in Apyrase 7 (APY7) were identified to suppress growth defects observed in lrx1 and fer mutants. APY7 encodes a Golgi-localized NTP-diphosphohydrolase, but opposed to other apyrases of Arabidopsis, APY7 revealed to be a negative regulator of cell growth. APY7 modulates the growth-inhibiting effect of RALF1, influences the cell wall architecture, and alters the pH of the extracellular matrix, all of which affect cell growth. Together, this study reveals a function of APY7 in cell wall formation and cell growth that is connected to growth processes influenced by the LRX/FER/RALF signaling module.

plant biology↗

bioRxiv2019

LRR-extensins of vegetative tissues are a functionally conserved family of RALF1 receptors interacting with the receptor kinase FERONIA

Plant cell growth requires the coordinated expansion of the protoplast and the cell wall that confers mechanical stability to the cell. An elaborate system of cell wall integrity sensors monitors cell wall structures and conveys information on cell wall composition and growth factors to the cell. LRR-extensins (LRXs) are cell wall-attached extracellular regulators of cell wall formation and high-affinity binding sites for RALF (rapid alkalinization factor) peptide hormones that trigger diverse physiological processes related to cell growth. RALF peptides are also perceived by receptors at the plasma membrane and LRX4 of Arabidopsis thaliana has been shown to also interact with one of these receptors, FERONIA (FER). Here, we demonstrate that several LRXs, including the main LRX protein of root hairs, LRX1, interact with FER and RALF1 to coordinate growth processes. Membrane association of LRXs correlate with binding to FER, indicating that LRXs represent a physical link between intra- and extracellular compartments via interaction with membrane-localized proteins. Finally, despite evolutionary diversification of the LRR domains of various LRX proteins, many of them are functionally still overlapping, indicative of LRX proteins being central players in regulatory processes that are conserved in very different cell types.\n\nAuthor SummaryCell growth in plants requires the coordinated enlargement of the cell and the surrounding cell wall, which is ascertained by an elaborate system of cell wall integrity sensors, proteins involved in the exchange of information between the cell and the cell wall. In Arabidopsis thaliana, LRR-extensins (LRXs) are localized in the cell wall and are binding RALF peptides, hormones that regulate cell growth-related processes. LRX4 also binds the plasma membrane-localized receptor kinase FERONIA (FER), establishing a link between the cell and the cell wall. It is not clear, however, whether the different LRXs of Arabidopsis have similar functions and how they interact with their binding partners. Here, we demonstrate that interaction with FER and RALFs requires the LRR domain of LRXs and several but not all LRXs can bind these proteins. This explains the observation that mutations in several of the LRXs induce phenotypes comparable to a fer mutant, establishing that LRX-FER interaction is important for proper cell growth. Some LRXs, however, appear to influence cell growth processes in different ways, which remain to be identified.

plant biology↗