Biology subjects

Haluska, S.

Publications and source records attributed to Haluska, S..

4 recordsLinked to original sources

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

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↗

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↗

bioRxiv2023

Phytohormone profiling in an evolutionary framework

Multiple phytohormones act as conserved developmental regulators in land plants. Although the closely related streptophyte green algae typically lack full complements of molecular pathways underlying these responses, scattered reports of endogenous phytohormone production in these organisms exist. In this study, we performed a detailed LC/MS-based analysis of several phytohormones, their precursors and metabolites in all lineages of streptophyte algae. We also included chlorophyte algae and early-diverging land plants as outgroups. Free auxin, tRNA-derived cytokinins and certain phenolics including salicylic acid were found ubiquitously. However, land plants differed from green algae by the consistent detection of abscisic acid and the presence of auxin and cytokinin conjugates and trans-zeatin, supporting the hypotheses that these three phytohormones likely came to regulate development in the ancestral land plant. By contrast, we observed a patchy distribution of jasmonates among streptophytes. We additionaly analyzed the corresponding culture and empty media to account for phytohormone excretion and environmental contamination. Extracellular auxins and cytokinins were frequently detected, while agar constituted a major external source of phenolic compounds. We provide a highly comprehensive evolution-directed screen of phytohormone compound occurrence and thoroughly discuss our data in the context of current plant hormonomics and phylogenomics. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/534998v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1532f4org.highwire.dtl.DTLVardef@1c4396borg.highwire.dtl.DTLVardef@195d0eborg.highwire.dtl.DTLVardef@c71b11_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗