Biology subjects

Zarsky, V.

Publications and source records attributed to Zarsky, V..

At least 19 recordsLinked to original sources

bioRxiv2026

Endogenous and environmentally modulated leaf shape plasticity in Boquila trifoliolata: how good is the evidence for mimicry?

Reports that the South American climbing vine Boquila trifoliolata modifies its leaf shape to mimic leaves of its host plant have raised considerable attention. Boquila leaf development was proposed to reflect visual inputs perceived in an unknown manner. However, the very existence of Boquila leaf shape mimicry remains inconclusive, since the reported observations are open to alternative explanations. We performed an initial quantitative characterization of leaf shape variability in glasshouse-cultured clonal Boquila plants grown without close host contact, and attempted to reproduce the leaf shape mimicry phenomenon under controlled culture conditions using live olive (Olea europaea) plants, artificial (decoy) olive or artificial ivy plants as supports. While we found leaves of variable shape (including those resembling ivy leaves) both in plants grown without host contact and in those climbing on live or decoy hosts, we did not observe any link between leaf shape and host presence or character. Instead, the leaf shape appears to be affected by environmental conditions including the season. Although our study was limited to a single Boquila genotype and an ecologically unrealistic host selection, our observations suggest that the alleged mimicry might originate from unintentional misinterpretation of intrinsic discontinuous leaf shape plasticity in field observations.

plant biology↗

bioRxiv2026

A plasmodesmata-specific exocyst complex regulates symplastic connectivity by affecting callose turnover

Plasmodesmata are intercellular channels that mediate symplastic communication between plant cells. Molecular transport through these channels is critically regulated by dynamic callose deposition and degradation, yet the secretory mechanisms that deliver regulatory components to plasmodesmata remain poorly understood. Here, we identify and characterize a non-canonical plasmodesmata-associated module of the exocyst, an evolutionarily conserved protein complex involved in secretory vesicle tethering and exocytosis. Exocyst subunits EXO70G1, SEC15A, EXO84C, and SEC10A specifically accumulate at plasmodesmata, whereas the canonical exocyst subunits EXO70A1 and SEC8 do not. Genetic and interaction analyses show that EXO70G1 acts as a landmark for recruiting SEC15A and EXO84C to plasmodesmata, revealing a distinct mode of exocyst targeting at these membrane domains. EXO70G1-dependent exocyst targeting to plasmodesmata depends on phosphoinositides and sphingolipids, consistent with the specialized lipid environment of plasmodesmal membranes. Loss of EXO70G1 results in increased callose accumulation and reduced symplastic transport, and strongly enhances developmental defects of a callose-overproducing mutant. In addition, exo70G1 mutants display enhanced resistance to bacterial pathogen Pseudomonas syringae, linking reduced plasmodesmal permeability to anti-bacterial defense. Cross-species analysis further indicates that plasmodesmata association is a derived feature of the EXO70G clade, present in angiosperms but absent from non-angiosperm EXO70 homologs. Together, our findings show that exocyst diversification in plants has generated a specialized trafficking module - plasmodesmata-associated exocyst - that links vesicle delivery to callose homeostasis at plasmodesmata, thereby regulating intercellular communication, development, and immunity. TeaserA specialized secretion module of the exocyst complex regulates plant cell-to-cell connectivity by controlling callose turnover at plasmodesmata

plant biology↗

bioRxiv2026

Arabidopsis exocyst complex subunit EXO70E2 in defence against Pseudomonas syringae in conjunction with autophagy

Exocyst was initially uncovered in yeast genetic sec-screen as a tethering complex for exocytotic vesicles and this function was later found to be evolutionarily conserved in other eukaryotes including plants. Later however, a surprising engagement of the exocyst complex in autophagy was observed in animals, plants and recently also in yeast. Using the genetic approach we observed EXO70E2 exocyst complex subunit engagement in the defence response to Pseudomonas syringae attack linked to the autophagy pathway. CRISPR/CAS LOF mutant of EXO70E2 is more sensitive to Pseudomonas infection (both virulent as well as T3SS mutant) and autophagy flux monitored by NBR1 antibody is compromised in comparison to WT. We conclude that the plant exocyst complex linked to the EXO70E2 subunit participates in defence against Pseudomonas bacteria in conjunction with the autophagy pathway. HighlightArabidopsis exocyst subunit EXO70E2 affects selective autophagic flux monitored by NBR1 and is participating in defense against Pseudomonas syringae infection.

plant biology↗

bioRxiv2026

Loss of PR1 function enhances Arabidopsis resistance to Botrytis cinerea

PATHOGENESIS-RELATED 1 (PR1) is one of the most widely used markers of salicylic acid (SA)-dependent plant immunity, yet its direct functional contribution to pathogen defence remains poorly understood. Here, we investigated the role of PR1 in Arabidopsis thaliana by analyzing a pr1 loss-of-function mutant challenged with bacterial and fungal pathogens and fumonisin B1 (FB1)-induced cell death. Notably, loss of PR1 led to markedly different responses to distinct pathogens; while it moderately increased susceptibility to the pathogenic bacterium Pseudomonas syringae, it substantially enhanced resistance to the necrotrophic fungus Botrytis cinerea, and the responses to the necrotroph Sclerotinia sclerotiorum remained unaltered. The pr1 mutant also displayed reduced spread of FB1-induced cell death, linking PR1 function to the promotion of stress-associated cell death. In line with the susceptibility changes, we observed the strongest PR1 accumulation and cell wall enrichment during B. cinerea infection using mCherry-tagged PR1 expressed under its endogenous promoter. Complementation with full-length PR1 and with a C-terminally truncated PR1 variant lacking the CAPE peptide restored wild-type susceptibility, whereas a non-cleavable PR1 variant did not. These results indicate that proteolytic processing at the CAPE cleavage motif, rather than the CAPE peptide itself, is required for PR1 function. Our data thus strongly suggest that PR1 may act as a susceptibility factor for necrotrophic pathogens by promoting host cell death.

Plant Biology↗

bioRxiv2026

MILDEW RESISTANCE LOCUS O (MLO) proteins function as trimeric inward calcium channels

Calcium signalling and structural roles are fundamental for plant growth, development, and environmental adaptation. Recent studies have identified MILDEW RESISTANCE LOCUS O (MLO) proteins as novel calcium-permeable channels with roles in root growth, cell wall development, pollen tube growth, and perception. However, the molecular mechanisms underlying MLO function remain unknown. Here, we demonstrate that multimerisation is essential for MLO activity. Chemical crosslinking, split-ubiquitin interaction assays, and single-molecule photobleaching revealed that MLO proteins form stable dimeric and trimeric assemblies at the plasma membrane. Structural modelling uncovered a molecular architecture of the MLO trimer with a central ion-conducting pore, which was further examined by molecular dynamics simulations in a lipid membrane environment. Computational electrophysiology showed preferential inward Ca2+ transport, confirming that MLO proteins function as calcium influx transporters, and identified a conserved set of pore-lining residues that coordinate ion translocation. Functional and structural analyses indicated that the mechanism of calcium permeation is evolutionarily conserved. Our findings provide mechanistic insight into MLO-mediated calcium influx across the plasma membrane and establish multimerisation as a critical determinant of this calcium channels activity.

plant biology↗

bioRxiv2026

Division of labor between seed plant RAB GDI paralogs: insights from genetic analysis in Arabidopsis thaliana

BackgroundRAB Guanine Nucleotide Dissociation Inhibitors (RAB GDIs) are important vesicle transport regulators in eukaryotes, participating in the functional cycle of RAB GTPases by stabilizing their non-active GDP-conformation. AimsWe address the importance of the three Arabidopsis thaliana RAB GDI paralogs by genetic and developmental analyses and put these results into the seed plants evolution context. MethodsWe use methods of genetics, microscopy and phylogenetics. ResultsOur genetic analyses of Arabidopsis T-DNA insertional mutants confirm recent CRISPR alleles data indicating lethality of double gdi1 gdi2 mutants, and our microscopic data point to embryo development arrest in double mutant seeds. We also confirm the involvement of GDI2 and GDI3 in pollen tube growth. Moreover, our data show that GDI1 also contributes to proper pollen function. Our phylogenetic analysis reveals independent diversification of RAB GDIs in Gymnosperms and Angiosperms, with early specialization of an Angiosperm reproduction-and gametophyte-related clade. ConclusionsIn Arabidopsis, RAB GDI1 and 2 are important for the vegetative growth while RAB GDI2 and 3 are vital for reproduction. Evolution of the RAB GDI family reflects the evolution of seed plants. HighlightsRAB GDIs are vital for plant growth and reproduction and act redundantly. Even the low-transcribed RAB GDI1 isoform contributes to the proper pollen function. Two RAB GDI clades evolved in early Angiosperms.

plant biology↗

bioRxiv2026

Evolutionary analysis of the exocyst complex in streptophytes links early EXO70 diversification with dominance over SEC3 in membrane targeting

The exocyst is a conserved octameric vesicle-tethering complex essential for targeted secretion. It is organized into two modules (I: SEC3, SEC5, SEC6, SEC8; II: SEC10, SEC15, EXO70, EXO84). In plants, the module II subunits SEC15, EXO84, and especially EXO70 have diversified into multiple subfamilies, yet the evolutionary origins and functional consequences of this diversification remain unclear. Here we reconstruct exocyst evolution across streptophytes using phylogenomic, functional complementation, and structural modeling analyses. We show that the three major EXO70 subfamilies originated in anydrophytes--the common ancestor of Zygnematophyceae and land plants--indicating that EXO70 diversification had begun at the dawn of plant terrestrialization. Complementation of Arabidopsis exo70 mutants with EXO70 paralogs from the liverwort Marchantia polymorpha and the streptophyte alga Klebsormidium nitens demonstrates that the ancestral canonical function is retained in the EXO70.1 lineage, whereas other subfamilies have undergone substantial functional specialization. We further uncover an evolutionary shift in exocyst membrane targeting: while Klebsormidium SEC3 retains autonomous membrane-recruitment capacity, land-plant SEC3 subunits have lost this ability, rendering exocyst targeting increasingly dependent on EXO70. Together, these findings suggest that early EXO70 diversification, combined with the redistribution of membrane-targeting functions within the exocyst, enabled paralog-specific exocyst recruitment and facilitated the emergence of specialized secretion pathways during plant terrestrialization. Significance StatementThe exocyst is a conserved protein complex that targets secretory vesicles to the plasma membrane across eukaryotes. In land plants, the EXO70 subunit diversified extensively, but the origins and consequences of this diversification remained unclear. We show that three major EXO70 subfamilies arose in the common ancestor of land plants and their closest algal relatives, at the dawn of plant terrestrialization. Cross-species complementation reveals that the EXO70.1 lineage retains the ancestral canonical function, whereas other subfamilies specialized. We further uncover an evolutionary shift in the mechanism of exocyst membrane targeting, from SEC3 toward EXO70, that could have enabled distinct EXO70 paralogs to direct secretion to different cellular sites during the colonization of land.

plant biology↗

bioRxiv2026

Absence of endosymbiotic gene transfer in symbiont-bearing diplonemids

Horizontal gene transfer (HGT) is one of the fundamental processes in the evolution of prokaryotic genomes, while its importance in eukaryotes is still debated. Some of the hallmark eukaryotic organelles, such as mitochondria and chloroplasts, are of an ancient endosymbiotic origin. The process of acquiring (and losing) new endosymbionts is dynamic and still ongoing in many lineages. Endosymbiotic gene transfer (EGT) between symbionts and their hosts has been considered as one of the major sources of overall HGTs in eukaryotes. Thanks to recent advances in genomics and microscopy, more and more endosymbionts are discovered in protists offering suitable models for the study of EGT and its impact on the host. Recently, the presence of holosporacean and chlamydiacean symbionts in the novel strains of marine euglenozoan flagellates of genus Rhynchopus has been discovered. Here, we present an analysis of the genomes and transcriptomes of five Rhynchopus strains and examine the extent of EGT/HGT and the role of endosymbiosis in shaping the nuclear genome of symbiont-bearing hosts. Our results have shown that there is no evidence of a recent EGT from either Holosporales or Chlamydiales symbionts. The absence of such transfers suggests that EGT or at least a stable retention of EGT genes is not a requisite for a successful endosymbiosis. Furthermore, our results show striking differences between patterns of detected HGTs among the Rhynchopus lineages pointing to a dynamic and largely neutral evolution of horizontally-acquired genes.

evolutionary biology↗

bioRxiv2025

Systematic Analysis of the EXO70 Gene Family in Kiwifruit Species: Evolutionary Selection and Potential Functions in Plant Immunity

BackgroundKiwifruit (Actinidia spp.) is a commercially and nutritionally valuable fruit crop that faces increasing challenges from pathogens, particularly Pseudomonas syringae pv. actinidiae (Psa). The exocyst complex, especially the EXO70 subunit, has been demonstrated to play a crucial role in vesicle trafficking and plant immune responses in model species such as Arabidopsis thaliana. However, the function and evolution of EXO70 genes in fruit crops remain largely unexplored. ResultsWe conducted a comprehensive genome-wide analysis of the EXO70 gene family across five Actinidia species using Arabidopsis EXO70 sequences as queries. A total of 217 EXO70 genes (23 to 54 paralogues per species) were identified and classified into three subfamilies and nine clades (EXO70A-EXO70I), consistent with previous classifications in other plant taxa. Phylogenetic reconstruction and microsynteny analyzes revealed lineage- and genus-specific expansions of EXO70C members, as well as species-specific expansion events, particularly within the EXO70E and EXO70H clades. To investigate potential immune functions, yeast two-hybrid and in planta co-immunoprecipitation assays confirmed that kiwifruit EXO70B1 physically interacts with the immune hub protein kiwifruit RIN4_1. These interactions support conservation of the EXO70-RIN4 module in plant immunity. ConclusionsThis study provides the first comprehensive characterization of the EXO70 gene family across multiple kiwifruit species and uncovers candidate genes potentially involved in plant immunity through RIN4-mediated defense signaling. Notably, the expansion and diversification of the EXO70E and EXO70H clades suggest possible adaptive evolution within these clades and neofunctionalization. These findings provide valuable genomic resources and novel insights into the evolution of vesicle trafficking components in fruit crops, laying the groundwork for future efforts to enhance disease resistance in kiwifruit through breeding or biotechnological approaches.

plant biology↗

bioRxiv2025

Salicylic acid accumulation correlates with low anthocyanin production in Arabidopsis

Anthocyanins, flavonoid pigments, are essential photoprotective agents and play a pivotal role in enhancing plant resilience to environmental stressors. It has been shown that anthocyanin production is inhibited when pattern-triggered immunity (PTI) is activated in Arabidopsis thaliana. An important component of PTI is the phytohormone salicylic acid (SA). Interestingly, exogenous treatment with SA has been shown to induce anthocyanin content in grape, apple, maize roots, rose callus, or Arabidopsis seedlings. In this study, we used several A. thaliana mutants with modulated SA content to decipher the role of endogenous SA in anthocyanin production in A. thaliana. We treated WT and mutants with anthocyanin-inducible conditions and measured anthocyanin content using spectroscopy. We showed that high endogenous SA accumulation correlates with low anthocyanin production. This was confirmed by the treatment of the A. thaliana seedlings with exogenous SA. Additionally, using microscopy in the 5gt mutant, which exhibits enhanced production of anthocyanin vesicular inclusions (AVIs) due to the inhibition of ligandin-dependent vacuolar import, we showed that high endogenous SA also correlates with lower AVI abundance. Comparative analysis of Arabidopsis WT and mutants used in this study indicates a possible inhibitory effect of SA accumulation on anthocyanin content under anthocyanin-inducible conditions (AICs). We suggest that under AICs, SA downstream signaling independent of NPR1 is responsible for lower anthocyanin accumulation. HighlightsO_LIHigh endogenous SA correlates with low anthocyanin content under AIC in Arabidopsis C_LIO_LISA signaling, not biosynthesis, is responsible for the inhibition of anthocyanins C_LIO_LIHigh SA concentration decreases the abundance of AVI bodies C_LI GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=146 HEIGHT=200 SRC="FIGDIR/small/658514v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@183500corg.highwire.dtl.DTLVardef@1fc5e3forg.highwire.dtl.DTLVardef@18fb48forg.highwire.dtl.DTLVardef@1975181_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphical abstract. Anthocyanin-inducible conditions (AICs), such as changes in day length, high sucrose in the medium, or treatment with kinetin, trigger the biosynthesis of anthocyanins. Previously, it was shown that activated pattern-triggered immunity (PTI), caused by the recognition of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs), inhibits anthocyanin production. A typical PTI response is an increased production of salicylic acid (SA). In this study, we show that a high concentration of SA and its downstream signaling, rather than SA biosynthesis itself, reduces anthocyanin accumulation.

plant biology↗

bioRxiv2024

The Arabidopsis Class I formin AtFH5 contributes to seedling resistance to salt stress.

The family of formins, evolutionarily conserved multidomain proteins engaged in the control of actin and microtubule cytoskeleton organization, exhibits considerable diversity in plants. Angiosperms have two formin clades consisting of multiple paralogs, Class I and Class II, the former being often transmembrane proteins located at the plasmalemma or endomembranes. According to available transcriptome data, the Arabidopsis thaliana Class I transmembrane formin AtFH5 (At5g54650) exhibits a distinct pattern of transcript abundance in various seedling root tissues with massive increase of transcript level upon salinity stress. To examine a possible role of AtFH5 in NaCl stress response, we generated transgenic plants expressing green fluorescent protein (GFP)-tagged AtFH5 under its native promoter and characterized its tissue and intracellular localization under standard culture conditions and under NaCl stress. While we confirmed the induction of AtFH5 expression by salt treatment, the distribution of tagged protein, with maxima in the border-like cells of the root cap, in the phloem and at lateral root emergence sites, did not reflect previously reported transcript abundance, suggesting posttranscriptional regulation of gene expression. Subcellular localization studies employing also membrane trafficking inhibitors suggested that AtFH5 protein level may be modulated by endocytosis and autophagy. Notably, loss-of-function atfh5 mutants exhibited increased sensitivity to NaCl stress, indicating that AtFH5 contributes to the development of seedling salt tolerance. These findings highlight the functional importance of AtFH5 in abiotic stress responses.

plant biology↗

bioRxiv2024

A Rab-Kinesin12-Fused kinase module couples vesicle delivery and phragmoplast remodelling during cytokinesis in Arabidopsis

Cytokinesis is a key process in the development of multicellular organisms, through both formative and proliferative divisions. In land plants, successful cytokinesis requires precise targeting of Golgi-derived vesicles to the future division plane by the phragmoplast, a cytoskeletal structure that undergoes continuous remodelling. Endomembrane trafficking and phragmoplast remodelling are tightly coupled, indicating the existence of active crosstalk. However, although many molecular regulators of membrane trafficking and cytoskeletal organisation are known, it remains poorly understood how these processes are co-ordinated. Here, we describe a regulatory module consisting of the membrane-associated GTPase RAB-A2a, cytoskeleton-associated Class II Kinesin-12s, and the Fused kinase orthologue TIO. We provide evidence that the interaction between these molecules at the midzone is essential for cytokinesis in Arabidopsis through simultaneously targeting vesicles to the midzone and coupling phragmoplast remodelling to vesicle delivery.

plant biology↗

bioRxiv2024

A genome-wide association screen for genes affecting leaf trichome development and epidermal metal accumulation in Arabidopsis

To identify novel genes engaged in plant epidermal development, we characterized the phenotypic variability of rosette leaf epidermis of 310 sequenced Arabidopsis thaliana accessions, focusing on trichome shape and distribution, compositional characteristics of the trichome cell wall, and histologically detectable metal ion distribution. Some of these traits correlated with climate parameters of ourq accessions locations of origin, suggesting environmental selection. A novel metal deposition pattern in stomatal guard cells was observed in some accessions. Subsequent GWAS analysis identified 1546 loci with protein sequence-altering SNPs associated with one or more traits, including 5 genes with previously reported relevant mutant phenotypes and 80 additional genes with known or predicted roles in relevant developmental and cellular processes. Some candidates, including GFS9/TT9, exhibited environmentally correlated allele distribution. Several large gene families, namely DUF674, DUF784, DUF1262, DUF1985, DUF3741, cytochrome P450, receptor-like kinases, Cys/His-rich C1 domain proteins and formins were overrepresented among the candidates for various traits, suggesting epidermal development-related functions. A possible participation of formins in guard cell metal deposition was supported by observations in available loss of function mutants. Screening of candidate gene lists against the STRING interactome database uncovered several predominantly nuclear protein interaction networks with possible novel roles in epidermal development.

plant biology↗

bioRxiv2024

Phylogenomics defines Streptofilum as a novel deep branch of streptophyte algae

Streptophytes constitute a major organismal clade comprised of land plants (embryophytes) and several related green algal lineages. Their seemingly well-studied phylogenetic diversity was recently enriched by the discovery of Streptofilum capillaum, a simple filamentous alga forming a novel deep streptophyte lineage in a two-gene phylogeny1. A subsequent phylogenetic analysis of plastid genome-encoded proteins resolved Streptofilum as a sister group of nearly all known streptophytes, including Klebsormidiophyceae and Phragmoplastophyta (Charophyceae, Coleochaetophyceae, Zygnematophyceae, and embryophytes)2. In a stark contrast, another recent report, published in Current Biology by Bierenbroodspot et al.3, presented a phylogenetic analysis of 845 nuclear loci resolving S. capillatum as a member of Klebsormidiophyceae, nested among species of the genus Interfilum. Here we demonstrate that the latter result is an artefact stemming from an unrecognized contamination of the transcriptome assembly from S. capillatum by sequences from Interfilum paradoxum. When genuine S. capillatum sequences are employed in the analysis, the position of the alga in the nuclear genes-based tree fully agrees with the plastid genes-based phylogeny. The "intermediate" phylogenetic position of S. capillatum predicts it to possess a unique combination of derived and plesiomorphic traits, here exemplified, respectively, by the "Rho of plants" (ROP) signaling system and the cyanobacteria-derived plastidial transfer-messenger ribonucleoprotein complex (tmRNP). Our results underscore S. capillatum as a lineage pivotal for the understanding of the evolutionary genesis of streptophyte, and ultimately embryophyte, traits.

plant biology↗

bioRxiv2023

Chitosan stimulates root hair callose deposition and inhibits root hair growth

Although angiosperm plants have a general capacity to react after the immunity elicitor chitin or chitosan treatment by the cell wall callose deposition, this response in particular cell types and its evolutionary conservation is not understood. Here we show that also the growing root hairs (RHs) of Arabidopsis can respond to a mild (0.001%) chitosan treatment by the callose deposition and by a deceleration of the RH growth. We demonstrate that the glucan synthase-like 5 (GSL5)/PMR4 is vital for chitosan-induced callose deposition but not for RH growth inhibition. Upon the higher chitosan concentration (0.01%) treatment, RHs do not deposit callose, while growth inhibition is prominent. To understand the specificities of the low and high concentration chitosan treatments, we analysed the corresponding PTI signalling components, gene expression, and RH cellular endomembrane and cytoskeleton modifications. Importantly, chitosan-induced callose deposition is also present in the functionally analogous and evolutionarily only distantly related RH-like structures rhizophores (lycophytes) and rhizoids (bryophytes). Our results point to the RH callose deposition as a conserved strategy of soil-anchoring plant cells (rhizoids/rhizophores/RHs) to deal with mild biotic stress. At the same time, high chitosan concentration prominently disturbs intracellular dynamics, tip-localised endomembrane compartments and RH growth, precluding callose deposition.

plant biology↗

bioRxiv2022

Interplay of EXO70 and MLO proteins modulates trichome cell wall composition and powdery mildew susceptibility

EXO70 proteins are essential constituents of the octameric exocyst complex implicated in vesicle tethering during exocytosis, while MLO proteins are plant-specific calcium channels of which some isoforms play a key role during fungal powdery mildew pathogenesis. We here detected by a variety of histochemical staining procedures an unexpected phenotypic overlap of A. thaliana exo70H4 and mlo2 mlo6 mlo12 triple mutant plants regarding the biogenesis of leaf trichome secondary cell walls. Biochemical and Fourier transform infrared spectroscopic analyses of isolated trichomes corroborated deficiencies in the composition of trichome cell walls in exo70H4 and mlo2 mlo6 mlo12 mutants. Transgenic lines expressing fluorophore- tagged EXO70H4 and MLO variants exhibited extensive co-localization of these proteins at the trichome plasma membrane and cell wall. Furthermore, mCherry- EXO70H4 mislocalized in trichomes of the mlo triple mutant and, vice versa, MLO6- GFP exhibited aberrant subcellular localization in trichomes of the exo70H4 mutant. Transgenic expression of GFP-marked PMR4 callose synthase, a previously identified cargo of EXO70H4 dependent exocytosis, revealed reduced cell wall delivery of GFP- PMR4 in mlo triple mutant plants. In vivo protein-protein interaction assays uncovered isoform-preferential physical interaction between EXO70 and MLO proteins. Finally, exo70H4 and mlo mutants, when combined, showed synergistically enhanced resistance to powdery mildew attack. Taken together, our data point to an isoform- specific interplay of EXO70 and MLO proteins in the modulation of trichome cell wall biogenesis and powdery mildew susceptibility, possibly by (co-)regulating focal secretion of cell wall-related cargo.

plant biology↗

bioRxiv2021

The EXO70B2 exocyst subunit contributes to papillae and encasement formation in anti-fungal defence in Arabidopsis

In the reaction to non-adapted Blumeria graminis f. sp. hordei (Bg), Arabidopsis thaliana leaf epidermal cells deposit cell wall reinforcements called papillae or seal fungal haustoria in encasements, both of which involve intensive exocytosis. A plant syntaxin SYP121/PEN1 has been found to be of key importance for the timely formation of papillae, and the vesicle tethering complex exocyst subunit EXO70B2 has been found to contribute to their morphology. Here, we identify a specific role for the EXO70B2-containing exocyst complex in the papillae membrane domains important for the callose deposition and GFP-SYP121 delivery to the focal attack sites, as well as its contribution to encasement formation. The mRuby2-EXO70B2 co-localises with the exocyst core subunit SEC6 and GFP-SYP121 in the membrane domain of papillae, and both proteins have the capacity to directly interact. The exo70B2/syp121 double mutant has a reduced number of papillae and haustorial encasements in response to Bg, indicating an additive role of the exocyst in SYP121 coordinated non-host resistance. In summary, we report cooperation between the plant exocyst and a SNARE protein in penetration resistance against non-adapted fungal pathogens. HighlightThe exocyst complex containing EXO70B2 subunit has specific role in papilla and encasement formation, implemented in coordination with the pathway regulated by the SYP121 SNARE complex in defence.

cell biology↗

bioRxiv2019

EXO70A2 is critical for the exocyst complex function in Arabidopsis pollen

Pollen development, pollen grain germination and pollen tube elongation are crucial biological processes in angiosperm plants that need precise regulation to deliver sperm cells to fertilize ovules. Pollen grains undergo two major developmental switches: dehydration characterized by metabolic quiescent state, and rehydration upon pollination that leads to extraordinary metabolic and membrane trafficking activity, resulting in germination and rapid tip growth of pollen tubes. To sustain these processes, many plant housekeeping genes evolved their pollen-specific paralogs. Highly polarized secretion at a growing pollen tube tip requires the exocyst tethering complex responsible for specific targeting of secretory vesicles to the plasma membrane. Here, we describe that EXO70A2 (At5g52340) is the main exocyst EXO70 isoform in Arabidopsis pollen, which governs the conventional secretory function of the exocyst, analogically to EXO70A1 (At5g03540) in the sporophyte. Our analysis of a CRISPR-generated exo70a2 mutant revealed that EXO70A2 is essential for efficient pollen maturation, pollen grain germination and pollen tube growth. GFP:EXO70A2 was localized similarly to other exocyst subunits to the apical domain in growing pollen tube tips characterized by intensive exocytosis. Moreover, EXO70A2 could substitute for the EXO70A1 function in the sporophyte, indicating functional redundancy of these two closely related isoforms. Phylogenetic analysis revealed that the ancient duplication of EXO70A to two (or more) paralogs, one of which is highly expressed in pollen, occurred independently in monocots and dicots. In summary, EXO70A2 is a crucial component of the exocyst complex in the Arabidopsis pollen required for efficient plant sexual reproduction.

plant biology↗