# Guanylate-binding proteins: emerging critical functions in plant development, immunity and stress response

Lucie Fernandez-lochu, Martine Lemaire-chamley, Christian Chevalier

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Lucie Fernandez-lochu, Martine Lemaire-chamley, Christian Chevalier. Guanylate-binding proteins: emerging critical functions in plant development, immunity and stress response. New Phytologist, 2025, 10.1111/nph.70524. hal-05267242

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Research review

Guanylate-binding proteins: emerging critical functions in plant
development, immunity and stress response

Authors for correspondence:

Lucie Fernandez-Lochu

Email: lucie.fernandez@inrae.fr

Christian Chevalier

Email: christian.chevalier@inrae.fr

Received: 5 May 2025

Accepted: 1 August 2025

**Lucie Fernandez-Lochu** [ID], **Martine Lemaire-Chamley** [ID] and **Christian Chevalier** [ID]

INRAE, Université de Bordeaux, UMR1332 Biologie du Fruit et Pathologie, Villenave d'Ornon, F-33140, France

Summary

Guanylate-binding proteins (GBPs) are large GTPases that belong to the Dynamin Superfamily Protein family. In humans, GBPs are well-characterized interferon-induced GTPases, playing a central role in cell-autonomous innate immunity against infections, inflammation and cancer. GBPs orthologs have been identified in plants only recently. Despite the limited number of reports describing their functional characterization, plant GBPs share common structural and biological features, as well as functions, with animal GBPs. This review aimed at highlighting the recent knowledge acquired on the critical role of GBPs and the associated mechanisms in plant developmental processes and in plant immunity to biotic aggressions through the control of gene expression.

New Phytologist (2025)

doi: 10.1111/nph.70524

**Key words:** biomolecular condensates, Dynamin Superfamily Protein, guanylate-binding protein, innate immunity, large GTPase, plant development, stress.

Introduction

Guanylate-binding proteins (GBPs) are large GTPases (LGs) that belong to the Dynamin Superfamily Proteins (DSPs; Ramachandran & Schmid, 2018). DSPs are mechano-enzymes characterized by a conserved N-terminal globular domain harboring the GTPase catalytic activity, followed by a highly variable extension providing various functional specializations (Jimah & Hinshaw, 2019). DSPs mediate membrane remodeling in several cellular processes through membrane fusion, fission and vesiculation (Jimah & Hinshaw, 2019), and cytoskeleton remodeling, especially in the context of cytokinesis (Konopka et al., 2006).

Among DSPs, the innate immune response to pathogens is
another well-characterized function, mostly assigned to GBPs.
GBPs are interferon-induced GTPases, whose founding member
HsGBP1 was identified in human fibroblasts following interferon
treatment (Cheng et al., 1983). Since this discovery, hundreds of
reports have described the implication of GBPs in cell-autonomous
innate immunity conferred against viral, bacterial and parasitic
infections, as well as in inflammatory response and cancer.

GBPs orthologs were identified in plants only recently. The first
article reporting the functional characterization of a plant GBP in

tomato was published in 2020 (Musseau *et al.*, 2020). Since then,
only five papers have been released, describing the function of GBPs
in *Arabidopsis*. Despite this scarcity, the literature shows never-
theless that plant GBPs share common structural and biological
features, as well as functions, with animal GBPs (Huang
*et al.*, 2019). This review aimed at highlighting the recent
knowledge acquired on the critical role of GBPs in plant
developmental processes, and in plant immunity to biotic
aggressions through the control of gene expression.

Structure, conformation and subcellular localization of
GBPs

Protein structure and conformation

The human HsGBP1 has been extensively structurally and
biochemically characterized, and serves as the structural model of
reference for animal GBPs (Prakash *et al.*, 2000). HsGBP1 is made
of 592 aa (MW of c. 68 kDa). It is constituted of two domains: the
LG N-terminal domain and the GTPase effector domain (GED) at
the C-terminus (Fig. 1a). The LG domain is made of α-helices and
β-sheets, and includes the catalytic sites involved in nucleotide
<figure><img src="image_4.png" /><figcaption>**Fig. 1** Domain structure of human HsGBP1, *Arabidopsis thaliana* (*At*) and tomato (*Solanum lycopersicum*, *Sl*) GBPs. (a) Domains and sequence motifs were predicted using the InterPro browser (https://www.ebi.ac.uk/interpro/protein/UniProt/). NLSs were predicted using the NLS-Mapper tool (https://nls-mapper.iab.keio.ac.jp/cgi-bin/NLS_Mapper_form.cgi). SMC-like domain were predicted using the NCBI BLASTP tool. LG domain, large GTPase domain; GED domain, GTPase effector domain; CaaX, isoprenylation motif; NES, nuclear export signal; NLS, nuclear localization signal; SMC-like domain, Structural Maintenance of Chromosome-like domain; SP, signal peptide; TMs, transmembrane domains; aa, amino acid; GBP, guanylate-binding proteins. (b) Alignment of GTPase (G) domains in HsGBP1, *Arabidopsis* and tomato GBPs. The G domain conferring nucleotide binding and hydrolysis is composed of four distinct structurally conserved motifs (G boxes; Jimah & Hinshaw, 2019). The G1 box or phosphate-binding loop (so-called P-loop; GxxxxGKS) binds the α- and β-phosphate of nucleotides. The G2 box includes a threonine that enables GTP hydrolysis, missing in AtGBP1. The G3 box (DxxG) anchors to the terminal γ-phosphate of nucleotide. The G4 box specifies the guanosine signature. Red outlines indicate mutated G2 and G3 box in the pseudo GTPase AtGBP1. Accession numbers are as follows: HsGBP1, P32455; HsGBP5, Q96PP8; AtGBP1, AT1G03830; AtGBP2, AT2G38840; AtGBP3, AT5G46070; SlGBP1, Solyc10g008950; SlGBP2, Solyc02g060770; SlGBP3, Solyc09g065810; and SlGBP4, Solyc06g084080.</figcaption></figure>

binding and hydrolysis (Fig. 1b). In the nucleotide-free state, the GED domain made of an elongated α-helical structure is locked to the LG domain, resulting in a closed monomeric conformation of

HsGBP1 (Prakash *et al.*, 2000; Fig. 2). This state corresponds to auto-inhibited GBP monomers with low intrinsic GTPase activity (Ghosh *et al.*, 2006). GTP binding to HsGBP1 induces sequential
<figure><img src="image_5.png" /><figcaption>**Fig. 2** Three dimensional model prediction of the structure of (a) human HsGBP1, (b) *Arabidopsis thaliana* AtGBPL2, tomato (*Solanum lycopersicum*) SIGBP3 and SIGBP4 as representative of plant guanylate-binding proteins (GBPs) from the AtGBPL2 clade, and (c) *Arabidopsis* AtGBPL1 and AtGBPL3, tomato SIGBP1 and SIGBP2 as representative of plant GBPs from the AtGBPL1/3 clade. Three dimensional models were predicted using the AlphaFold Protein Structure Database ([https://alphafold.ebi.ac.uk/](https://alphafold.ebi.ac.uk/)). The color code corresponds to domains illustrated in Fig. 1: blue, large GTPase (LG) domain; yellow, GTPase effector domain (GED); gray, coiled-coil regions; red, transmembrane (TM) domains; N, N-terminal end; C, C-terminal end.</figcaption></figure>

conformational changes promoting protein dimerization via LG domains, GEDs opening and dimer mutual interaction/stabilization, leading to stimulation of GTPase activity and further GTP hydrolysis (Ghosh et al., 2006; Ince et al., 2021; Weismehl et al., 2024). This open conformation corresponds to an activated dimeric state of GBPs able to oligomerize to form polymers (Sistemich et al., 2020; Weismehl et al., 2024; Zhu et al., 2024). In the dimerized and polymerized state, some GBPs, including HsGBP1, have the unique ability to hydrolyze GTP into GMP in two consecutive hydrolysis steps (Britzen-Laurent et al., 2010; Ince et al., 2017). Upon GTP, GDP or GMP dissociation, GBPs return to a closed monomeric conformation.

Plant GBPs display the conserved LG and GED domains (Figs 1, 2). However, structure prediction and phylogenetic analyses demonstrated that plant GBPs belong to two different clades (Reimann et al., 2023). A first clade, within a size range of 1000–1100 aa (110–125 kDa), is characterized by a long C-terminal extension, with coiled-coil regions, an intrinsically disordered region (IDR) and one or two nuclear localization signals (NLS; Huang et al., 2021; Reimann et al., 2023; Fig. 1a). This clade, termed the AtGBPL1/3 clade, encompasses the *Arabidopsis thaliana* AtGBPL1 and AtGBPL3, as well as the tomato (*Solanum lycopersicum*) SIGBP1 and SIGBP2. Within this clade, AtGBPL3

and SIGBP1/2 harbor STRUCTURAL MAINTENANCE OF CHROMOSOMES (SMC)-like domains, found in SMC proteins (Uhlmann, 2016). SMC proteins are involved in the compaction of genomes, as well as sister chromatid cohesion and segregation during cell division (Uhlmann, 2016). Hence, the presence of SMC domains may confer to AtGBPL3 and SIGBP1/2 a function during mitosis together with the ability to bind chromatin DNA. Members of the second clade, termed the AtGBPL2 clade, encompassing AtGBPL2 and the tomato SIGBP3 and SIGBP4, resemble HsGBP1, with a size of c. 600 aa and a MW of c. 69 kDa. They possess a shorter C-terminal extension devoid of coiled-coil and IDR regions. This C-terminal extension is characterized by the presence of several transmembrane (TM) domains, similarly to the animal ATLASTIN (ATL). ATL proteins are DSPs, involved in the fusion of endoplasmic reticulum (ER) membranes and ER-Golgi vesicle trafficking (Jimah & Hinshaw, 2019). A recent study indicated that AtGBPL2 might be the plant counterpart of animal ATL1 (Pan et al., 2025).

Reimann et al. (2023) mined more than 200 plant GBPs in a phylogenetic analysis. The number of GBP members in both clades varies according to the plant species. Additionally, the comparison of primary sequences provides a first glance at different functional roles among plant GBPs. GBPs within the AtGBPL2 clade share a
high degree of amino acid identity (c. 70–80% overall identity). Inside of the AtGBPL1/3 clade, GBP orthologs display a 60–70% overall amino acid identity. However, the LG domain of AtGBPL1 shares only c. 35% identical residues with AtGBPL3, SlGBP1/2, or animal GBPs. In particular, the AtGBPL1 protein sequence within the G2-, G3- and G4 box of the GTPase (G) domain is highly divergent when compared to other plant GBPs and HsGBP1 sequences (Fig. 1b). Such a mutated catalytic domain provides defective GTPase activity to AtGBPL1 (Huang *et al.*, 2021). Interestingly, this characteristic of a pseudo GTPase found in AtGBPL1 seems to be exclusive to Brassicaceae species. Both AtGBPL3 and AtGBPL2 harbor GTPase activity and are able to produce GDP, but not GMP (Huang *et al.*, 2021; Reimann *et al.*, 2023).

Whether the biochemical and enzymatic attributes found in animal GBPs also contribute to plant GBP conformation and dimerization remains largely uncharacterized. However, AtGBPL3 is able to dimerize via the nucleotide-dependent self-association of the LG domain, required for GTPase activity, and via the self-association of the GED domain (Reimann *et al.*, 2023). Whether homo- or heterodimerization occurs *in planta* remains to be demonstrated. Yet, evidence for a direct interaction between AtGBPL3 and AtGBPL1 inside of the nucleus, and AtGBPL3 and AtGBPL2 were provided (Huang *et al.*, 2021; Pan *et al.*, 2025).

## Subcellular localization of GBPs

HsGBPs differ in their cellular localization according to the presence of a CaaX isoprenylation motif at the C-terminal end serving for membrane anchoring (Fig. 1a). HsGBP1/2/5 harbor this motif and are located at membranes of various cellular compartments (Britzen-Laurent *et al.*, 2010; Sistemich *et al.*, 2021). In the absence of this motif, HsGBPs are homogeneously located in the cytosol and/or the nucleus (Tripal *et al.*, 2007; Britzen-Laurent *et al.*, 2010).

The binding of HsGBPs to membranes not only requires the presence of an isoprenyl moiety, but most importantly its accessibility. Indeed, under the closed monomeric conformation, the isoprenyl tail of HsGBP1 is positioned in a hydrophobic pocket of the GED domain, thus preventing its interaction with membranes (Sistemich *et al.*, 2021). GTP binding drives the open conformation, which releases the isoprenyl tail and renders it accessible for membrane anchoring (Shydlovskyi *et al.*, 2017; Sistemich *et al.*, 2021). Remarkably, the HsGBP1 C-terminal isoprenylation is required for the formation of highly polymerized structures, encompassing as much as thousands of molecules (Sistemich *et al.*, 2020; Weismehl *et al.*, 2024). Recently, Zhu *et al.* (2024) demonstrated the major role of these HsGBP1 conformational changes in the establishment of a host defense platform for cell-autonomous immunity, assembling nearly 30 000 HsGBP1 molecules. Besides its ability to target membranes, it is noteworthy that HsGBP1 appears also as granular/vesicular structures distributed throughout the cytoplasm, which are associated exclusively with the cytoskeleton (Ostler *et al.*, 2014; Tipton *et al.*, 2016).

Plant GBPs lack the C-terminal CaaX motif found in HsGBP1/2/5. However, *Arabidopsis* and tomato orthologs of the AtGBPL2 clade have an N-terminal signal peptide and three TM helices in the C-terminal extension (Fig. 1a), predicting their targeting and integration into the endomembrane system. Indeed, AtGBPL2 localizes to the tonoplast (Reimann *et al.*, 2023), as well as to the ER (Pan *et al.*, 2025), as expected for an ATL-like protein. Although AtGBPL2 possesses an NLS in its C-terminus, involved in nuclear import, it also presents in tandem a nuclear export signal (NES) domain responsible for its cytosolic localization, similarly to ATL1. When this NES domain is mutated, the ER localization of AtGBPL2 is abolished, and AtGBPL2 relocalizes to the nuclear envelope (NE; Pan *et al.*, 2025). *Arabidopsis* and tomato homologs of the AtGBPL1/3 clade also possess one or two NLSs in their C-terminus, but no NES domains (Fig. 1a). AtGBPL1/3 and SlGBP1/2 are indeed nuclear localized (Huang *et al.*, 2021), according to different sublocalizations within the nucleus (Fig. 3a). More precisely, AtGBPL3 accumulates mainly at endogenous levels at the inner membrane of the NE, where it is enriched at the nuclear pore complex (NPC) during interphase (Tang *et al.*, 2022; Reimann *et al.*, 2023). During mitosis, AtGBPL3 localizes as speckles surrounding the condensing chromosomes; it then localizes to the inner hemisphere of the daughter nuclei during telophase and to the newly formed envelope during cytokinesis (Reimann *et al.*, 2023). Such AtGBPL3 speckles are promoted by enhanced nucleotide-dependent self-association of the LG domain resulting from locally stimulated AtGBPL3 GTPase activity.

Notably, the distribution of AtGBPL3 in pollen grains and pollen tubes is very singular, as it is absent from NE but accumulates homogeneously in the nucleoplasm (Reimann *et al.*, 2023).

A remarkable feature of plant GBPs is their ability to form biomolecular condensates, which assemble in dynamic membrane-less organelles through liquid-liquid phase separation (LLPS) within the nucleus (Huang *et al.*, 2021). The LLPS process is driven by the association of multiple IDR-containing proteins involved in developmental or environmental cues, such as in plant immunity and stress response (Wang & Gu, 2022; Solis-Miranda *et al.*, 2023). Even in the absence of any exposure to stress, the overexpression of *Arabidopsis* and tomato GBPs also leads to the formation of such droplet-like condensates of variable range of size, at the nuclear periphery and/or within the nucleoplasm (Huang *et al.*, 2021; Tang *et al.*, 2022; Reimann *et al.*, 2023; Fig. 3a). Indeed, LLPS is a function of molecule concentration, and increased GBP nuclear concentration is sufficient to induce GBP condensates (Huang *et al.*, 2021). Although IDRs are necessary for the formation of GBP condensates, GTPase activity is also required. Whether LLPS-associated GBP condensates formed upon stress or over-expression and speckles found during mitosis are similar structures remains to be determined.

Plant GBPs belonging to the AtGBPL2 and AtGBPL1/3 clades are either cytosolic or nuclear, respectively. Moreover, different subnuclear localizations have been evidenced for the AtGBPL1/3 clade that seem to influence their diverse biological functions in plants (Fig. 3b), as described in the following section.
<figure><img src="image_6.png" /><figcaption>**Fig. 3** Subnuclear localization and multifunctional roles of plant guanylate-binding proteins (GBPs) of the AtGBPL3/1 clade. (a) The ability of plant GBPs to drive liquid-liquid phase separation (LLPS) according to their nuclear concentration redefines their subnuclear localization. At endogenous levels, GBPs are in dispersed form, mainly localized at the inner membrane of the nuclear envelope (NE). At high protein concentration, upon overexpression, stress or likely endoreduplication, GBPs form condensates of different sizes either localized at the NE (intermediate phase) or in the nucleoplasm (separated phase). (b) The subnuclear localization of GBPs is associated with diverse biological functions in plants. During development, GBPs are localized at the NE. There, GBPs participate in nuclear morphogenesis during interphase, within a complex encompassing CRWN1&4 and KAKU4, at the nuclear pore complex of the NE. The AtGBPL3/CRWN1&4/KAKU4 complex interacts with chromatin, where it recruits chromatin remodelers and participates in the regulation of gene expression and mRNA processing. GBPs are involved in the reformation of the NE during mitosis, as a result of the AtGBPL3/CRWN1&4/KAKU4 complex disassembly and the massive accumulation of AtGBPL3 into speckles at sites of active NE reformation. GBPs play a crucial role in tissue differentiation and cell fate during fruit growth by maintaining endopolyploid cells in a nonproliferative state that affects the cytoskeleton network and/or controls the expression of endoreduplication-associated and mitosis-associated genes, respectively, positively and negatively. During innate immunity and in response to stress, GBPs form LLPS-driven condensates, which localize within the nucleoplasm. Within condensates, GBPs bind directly to promoters of defense-related genes and recruit transcriptional coactivators of the Mediator complex and RNA polymerase II machinery to ensure the transcriptional reprogramming induced by immune activation. During gametophyte development and pollen grain formation, GBPs localize to the entire nucleoplasm, but the mechanisms and GBP interacting protein network are still undeciphered. Arrows and blunt-ended arrows represent positive and negative regulation, respectively. GBPs are represented in green; NE, nuclear envelope; OM, outer membrane; IM, inner membrane; EndoR, endoreduplication; OE, overexpression; NPC, nuclear pore complex; TF, transcription factors; PolII, RNA polymerase II.</figcaption></figure>
## Multifunctional roles of GBP in plants

According to their pivotal role in cell-autonomous innate immunity, in response to cancer, inflammation and infection (for reviews see Ngo & Man, 2017; Honkala et al., 2020; Kirkby et al., 2023), animal GBPs are described as the ‘guardians of host defense in health and disease’ (Tretina et al., 2019). Part of these functional roles and associated cellular mechanisms is conserved in plants, especially regarding intranuclear signaling for immunity against pathogens (Huang et al., 2019). Moreover, GBPs acquired specific functions in plants related to nuclear architecture and their ability to bind DNA, thus exerting a direct control on gene expression (Fig. 3b).

## Plant GBP and nuclear morphogenesis and activity

The NE localization of AtGBPL3 at endogeneous level is due to its interaction with the plant lamins CRWN1, CRWN4 and KAKU4 and the nucleoporin NUP136 of the nuclear pore basket (NB; Reimann et al., 2023; Tang et al., 2022; Fig. 3b). The nuclear lamina (also named nucleoskeleton) is a dense fibrillary network beneath the inner nuclear membrane that associates with NPC. The lamina is essential to ensure the structural integrity of the NE and specific perinuclear chromatin anchoring, thereby regulating the overall nuclear morphology and activity (Wang et al., 2022). AtGBPL3 recruited at the nuclear lamina in an AtGBPL3/CRWN1&4/KAKU4 protein complex is crucial for proper nuclear morphogenesis in differentiating cells during interphase. Indeed, the disruption of AtGBPL3 induces altered nuclear size and shape (Reimann et al., 2023), similarly to defective lamin mutants (Cao et al., 2024; Hu et al., 2019).

AtGBPL3 is not only involved in nuclear architecture, but it also plays a major part in chromatin modification and organization, transcription initiation and regulation, and RNA splicing and processing (Tang et al., 2022). These functions are in accordance with the role of lamina and NPC in coordinating the functional organization of the genome by anchoring a large fraction of the silent heterochromatin to the nuclear periphery (Strambio-De-Castillo et al., 2010). AtGBPL3 binds to chromatin at interphase, most likely via its SMC-like domains (Fig. 1a), and especially at the pericentromeric heterochromatin and/or peri-nuclear heterochromatin, which are highly subjected to the repressive H3K27m3 histone modification (Reimann et al., 2023). This mechanism involves the interaction of AtGBPL3 with CRWN1 at the lamina, and PWWP DOMAIN INTERACTOR OF POLYCOMB 1 (PWO1), a Polycomb Repressive Complex 2 (PRC2) associated protein mediating the deposition of the H3K27m3 repressive mark (Tang et al., 2022; Reimann et al., 2023). However, AtGBPL3 also binds euchromatin and promoter regions of transcriptionally active genes, as it recruits both activators and repressors of gene expression (Huang et al., 2021; Tang et al., 2022). Hence, AtGBPL3 may contribute in diverse combinations with lamins to a more dynamic regulation of gene expression at NPC than only repression of heterochromatin (Fig. 3b). Plants disrupted for AtGBPL3 present stunted growth; this phenotype is enhanced in the presence of mutated lamins and

NB proteins, leading to early senescence. Within this lamina/NPC network, plant GBPs emerge as novel major architectural and regulatory components of the nucleus, essential for plant vegetative growth and survival by maintaining nutrient homeostasis and suppression of stress responses under normal conditions. It is noteworthy that this function of AtGBPL3 in nuclear architecture, NE localization and transcriptional regulation at NE does not require the GTPase activity (Reimann et al., 2023).

In the next section, additional roles of nuclear GBPs during plant development will be described in relation to their subnuclear localizations.

## GBPs and the control of cell division during plant development

AtGBPL3 is highly expressed in the root apical meristem (RAM), where it is required for proper mitosis and is thus essential for root growth (Reimann et al., 2023). NE breakdown at mitosis triggers the disassembly of the AtGBPL3/CRWN1&4/KAKU4 complex. However, AtGBPL3 remains extensively co-localized with CRWN4, in the form of nuclear speckles surrounding the condensing prophase chromosomes and at the inner hemisphere of the daughter nuclei at telophase. During mitosis, AtGBPL3 is required for the reformation of the NE in the daughter cells (Reimann et al., 2023), likely resulting from the massive AtGBPL3 speckle accumulation at sites of active NE expansion (Fig. 3b). Although the exact role of AtGBPL3 speckles during mitosis remains unclear, Reimann et al. (2023) suggested a function in the recruitment of NE-associated proteins to remodel the NE during root development. When AtGBPL3 is mutated, the RAM displays a defective tissue patterning, with fewer and severely deformed cells, as well as aberrant cell wall positioning (Reimann et al., 2023). AtGBPL3 mutants also exhibit altered growth in shoot (Tang et al., 2022), but whether these alterations result from similar mechanisms is not known. Whatever these mechanisms are, the GTPase activity and the disordered CC region seem to be essential for AtGBPL3 function in both root and shoot development (Tang et al., 2022; Reimann et al., 2023).

In tomato, SIGBP1 controls fruit growth (Musseau et al., 2020). Tomato fruit growth proceeds from a first intense period of cell divisions, followed by endoreduplication-driven cell expansion, accounting for final fruit size (Mauxion et al., 2021; Tourdot et al., 2023). The disruption of SIGBP1 induces lower endoreduplication levels, thereby reducing cell sizes, and untimely abnormal cell wall patterning within the fruit tissue, resulting from the division of endoreduplicated cells (Musseau et al., 2020). In addition, the expression patterns of known endocycle and mitotic cycle regulators are modified (Fig. 3b). Therefore, SIGBP1 plays a crucial role in maintaining differentiated (endopolyploid) cells in a nonproliferative state, thus acting as inhibitors of cell division during fruit growth. How this repression on cell division occurs is still undeciphered. Such an antiproliferative function could involve remodeling of the cytoskeleton network, as do human GBPs during cancer (Ostler et al., 2014; Wandel et al., 2017). However, since a GBP inhibition of cell proliferation genes occurs in tomato fruit, a deactivation of the Hippo signaling pathway (Wu & Guan, 2021)
could occur in plant cells, as demonstrated for the human GBPs in
cancer cells (Unterer *et al.*, 2018). Homologs of the TEA-Domain
transcription factor (TF), whose direct interaction with HsGBP1
leads to the deactivation of the Hippo pathway (Unterer
et al., 2018), have not yet been identified in plants. However,
plant cells do possess homologs of the upstream regulatory Hippo
kinases (Musseau *et al.*, 2020).

Although poorly investigated, another role of plant GBPs seems
to emerge during pollen development. While *Arabidopsis* knock-
out mutants of AtGBP1 and AtGBP2 are fertile, the disruption
of AtGBP3 via CRISPR-Cas9 gene editing or homozygous
T-DNA insertions in the coding region leads to sterility (Huang
et al., 2021; Tang et al., 2022; Reimann et al., 2023). As
AtGBP3 is highly expressed in the male gametophyte (Reimann
et al., 2023), this sterility is due to defective pollen grain
formation, indicating that AtGBP3 is essential for gametophyte
development. Additional mechanisms associated with AtGBP3
and the interacting protein network are likely to be involved in
relation to its unique nucleoplasmic localization in pollen grain
when compared to other tissues/organs (Reimann et al., 2023;
Fig. 3b).

Plant GBPs thus display multifaceted roles during cell division either as a positive actor, likely establishing a structural basis for molecule tethering, or as a negative regulator via gene expression control, both required for proper tissue patterning. In the following section, we will address how GBPs turn out to be major players in biotic and abiotic stress responses.

GBPs in plant immunity and response to stress

Originally, AtGBP1 and AtGBP3 were identified from a
proteomic analysis aimed at isolating IDR-containing proteins
that could form LLPS-driven condensates within the nucleus in
response to biotic stress (Huang *et al.*, 2021). Indeed, the AtGBP3
condensates induced under bacterial infection or under over-
expression confer an increased resistance to infection, compared
with the *atgbpl3* hypomorphic mutants more susceptible to
pathogens (Huang *et al.*, 2021). Interestingly, an *atgbpl1* mutant
also shows an increased resistance, which can be abolished by the
introduction of the *atgbpl3* mutation. This led to the conclusion
that the pseudo GTPase AtGBP1 could be a negative allosteric
regulator of AtGBP3. The immune activation triggers an
allosteric switch where AtGBP1 no longer sequesters the
catalytically active AtGBP3 (Huang *et al.*, 2021). As a result,
AtGBP3 is free to reallocate to the nucleoplasm where it
concentrates in biomolecular condensates, called GBPL
defense-activated condensates (GDACs; Huang *et al.*, 2021;
Fig. 3a). AtGBP3 in condensate form binds directly to promoters
of defense-related genes and recruits transcriptional coactivators
of the Mediator complex and RNA polymerase II machinery to
ensure the transcriptional reprogramming induced by immune
activation (Fig. 3b). Among these defense-related genes, AtGBP3
is recruited to the promoters of genes involved in the salicylic acid
(SA) pathway, a major hormone mediating plant defense against
pathogens. These genes include *ICS1*, which encodes ISOCHOR-
ISMATE SYNTHASE 1, the key enzyme for SA production

(Huang *et al.*, 2021). In addition, AtGBP3 within GDACs regulates the transcription of two functionally redundant TFs that bind to the promoter of *ICS1* in response to SA, namely CALMODULIN-BINDING PROTEIN 60 g (CBP60g) and SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1; Kim *et al.*, 2022).

The formation of nuclear GDACs is reduced at elevated growth
temperature, which suppresses the recruitment of AtGBP3 to
the *CBP60g* and *SARD1* promoters, impairing SA biosynthesis (Kim
et al., 2022). This discovery shed light on the
temperature vulnerability of the SA pathway (Castroverde &
Dina, 2021), and the impact of heat stress on basal and
pathogen-induced immunity (Huot et al., 2017). Some GBP
condensates are temperature-insensitive and target different gene
promoters, but their role in stress response is not yet established (Kim
et al., 2022). As smaller droplets fuse into larger droplets during
LLPS according to molecule concentration (Huang et al., 2021;
Fig. 3a), it is likely that different GBP condensate types coexist
according to nuclear protein concentration and interacting proteins,
with possibly different roles during plant development.

A role in immunity was recently evidenced for plant cytosolic
GBP of the AtGBP2 clade (Pan et al., 2025). AtGBP3, with
AtGBP2, belongs to a signaling pathway that acts downstream of
CONSTITUTIVE EXPRESSION OF PR GENES 5 (CPR5) to
modulate plant immunity and counteract the NPC-located
nucleoporin CPR5 function. CPR5 acts as a key negative regulator
of plant effector-triggered immunity (ETI; Wang et al., 2014) in
preventing nuclear import of immune signals and core cell-cycle
inhibitors, thereby inactivating the immune response and induced
programmed cell death (PCD; Zhang et al., 2025). Plants with
disrupted CPR5 function exhibit elevated SA content, auto-
immune activation and spontaneous PCD, resembling ETI. A
gain-of-function mutation that disrupts the NES motif present in
AtGBP2 (Fig. 1a) was identified as a suppressor of the cpr5
mutation. As a consequence, the mutated AtGBP2 is reallocated
from the ER to the NE, where it activates AtGBP3 via its GTPase
activity, thereby suppressing the cpr5 mutant phenotype (Pan
et al., 2025).

Although the function of the wild-type AtGBP2 in immunity
is still undeciphered, these findings stress how important the
subcellular compartimentalization of plant GBPs is in regulating
the plant immune response. Indeed, NES-containing GBPs from the
AtGBP2 clade are prone to being exported from the nucleus
despite the presence of an NLS motif. In the absence of a functional
NES, these GBPs are susceptible to intervening in biological processes
close to that assigned to GBPs from the AtGBP1/3 clade, that is
development and plant immune response, thus modifying their
native function. Therefore, plant cytosolic (ER) GBPs are likely to
share the same processes with nuclear-located GBPs, most probably
via different mechanisms, but according to intertwined pathways, as to
optimize a trade-off between plant growth and immunity.

Conclusions and future directions

Despite evolutionary acquired differences in protein structure and
conformation, as well as in subcellular localization, animal and
plant GBPs do conserve functional similarities resulting from
adaptations within the two phyla. The GTPase activity, the
dimerization and formation of highly polymeric structures,
the interaction with multiple protein partners and formation of
multivalent protein complexes are among the conserved biochem-
ical properties. These properties provide GBPs multifunctional
roles in response to developmental and stress stimuli, and in cell-
autonomous innate immunity. GBPs participate in the regulation
of cell division with pro- and antiproliferative activity, in cell
differentiation and organismal development, leading to diseases in
animals and altered tissue patterning in plants if impeded. Plant
GBPs are able to mediate membrane- and/or cytoskeleton
remodeling, an activity typical of DSP LGs.

However, the ability of AtGBPL3 to interact with chromatin, where it recruits chromatin remodelers, and participates in the regulation of gene expression and mRNA processing, represents the greatest difference between plant and animal GBPs reported so far. In plant immune response, GBP condensates represent a cellular centralized organization aimed at regulating gene expression to protect against phytopathogen infection. This function in plant immunity involves the regulation of SA signaling, a major hormone in plant responses to biotic and abiotic stress, and in plant physiology and development (Rivas-San Vicente & Plasencia, 2011; Spoel & Dong, 2024). Whether GBP condensates may assemble in the context of abiotic stresses and regulate other cellular processes in plant growth and development will be worth investigating.

So far, the understanding of the biological functions of plant
GBPs is only at its dawn. New roles and mechanisms will arise from
further investigations addressing, for instance, pollen grain
formation or the still poorly characterized GBPs from the
AtGBPL2 clade.

Acknowledgements

This work was carried out with the financial support of the French
Agence Nationale de la Recherche and authors have applied a CC-
BY public copyright license (grant no.: ANR-24-CE20-5404) and
University of Bordeaux (RIE grant no: 2023 M&M Fruit).

Competing interests

None declared.

Author contributions

LF-L and CC conceptualized and designed the manuscript. LF-L,
ML-C and CC wrote the manuscript.

ORCID

Christian Chevalier ID https://orcid.org/0000-0002-5727-6206

Lucie Fernandez-Lochu ID https://orcid.org/0000-0003-0006-658X

Martine Lemaire-Chamley ID https://orcid.org/0000-0002-7687-894X

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