ABSTRACT The Min system disassembles FtsZ‐rings after septation in Bacillus subtilis and is localized to the nascent division plane and cell poles by the protein MinJ. The N‐terminal region of MinJ contains transmembrane segments while the C‐terminal region contains a PDZ domain, but its membrane topology and functional domains are poorly understood. Here, we empirically tested competing topology models and found that MinJ is a nine‐pass transmembrane protein with an extracellular N terminus and a cytoplasmic C terminal PDZ domain. Deletion of the PDZ domain resembled a MinJ null mutation but retained polar localization and interaction with both MinD and DivIVA. Deletion of transmembrane segments 6 and 7 abolished polar localization and interaction with MinD and DivIVA but conferred a hyper‐minicell phenotype that was additive in the absence of MinD. Structural prediction by AlphaFold3 suggests that segments 6 and 7 may constitute an unusual transmembrane β‐sheet, making MinJ perhaps the first of its kind to have such a secondary structure in the plasma membrane. Finally, phylogenetic analyses and structural comparison showed that MinJ sequence and structure are highly conserved within the Firmicutes and tightly co‐conserved with MinD and DivIVA with which it interacts. Our work clarifies the membrane topology and functional organization of MinJ and supports models in which MinJ contributes to bacterial cell division through mechanisms beyond canonical Min system regulation.
ABSTRACT The mechanistic target of rapamycin (mTOR) signaling pathway is a central regulator of nutrient sensing, metabolism, growth, and stress adaptation in most eukaryotes. Malaria parasites of the genus Plasmodium , however, lack identifiable orthologues of mTOR kinase and its associated signaling complexes, raising the question of how these organisms coordinate environmental sensing with developmental progression and proliferation. Here, we discuss emerging evidence suggesting that Plasmodium has evolutionarily replaced the canonical mTOR signaling axis with a distributed regulatory architecture composed of parasite‐specific nutrient sensors, kinase‐based signaling pathways, translational repression mechanisms, and unconventional autophagy processes. Components such as KIN, PI3K, eIF2α kinases, eIF4E‐interacting protein DOZI, and Maf1 collectively preserve many hallmark outputs of mTOR signaling, including metabolic adaptation, stress tolerance, developmental plasticity, and reversible quiescence. In addition, malaria parasites interact with host mTOR pathways during infection, potentially exploiting host‐derived anabolic signaling environments to support intracellular development. These findings suggest that Plasmodium exemplifies an extreme case of signaling plasticity in eukaryotic evolution, demonstrating how essential mTOR‐associated functions can be maintained despite the apparent loss of the pathway itself.
Although α-1,3-glucan represents a major polymer in cell walls of filamentous plant pathogenic fungi, its role in vegetative and pathogenic development is poorly understood. The maize anthracnose fungus Colletotrichum graminicola differentiates elaborate appressoria on the leaf surface and exhibits a hemibiotrophic lifestyle after host invasion. Promoter-eGFP-fusion analyses of all three α-1,3-glucan synthase (AGS) genes, designated as AGS1, AGS2, and AGS3, suggest that AGS3 is expressed in vegetative and pathogenic hyphae, whereas expression of AGS1 and AGS2 was not, or barely, detectable. Targeted gene deletions yielded single and double deletion mutants, as well as triple mutants, which lacked the entire repertoire of α-1,3-glucan synthase genes. Conidia of mutants lacking AGS3 developed multiple germ tubes, and vegetative hyphae had cell walls containing strongly reduced amounts of alkali-soluble glucose, showed hyperbranching, reduced growth rates on all substrata tested, and hypersensitivity to the cell wall-perturbing agents Caspofungin and Nikkomycin Z. Moreover, mutants lacking AGS3 exhibited strong virulence defects and, intriguingly, biotrophic hyphae of these mutants that differentiated in planta were severely misshapen. Increased cell wall pore diameters, increased mobility of uncharged dextran-FITC conjugates through cell walls of AGS3-deficient mutants and lack of PAMP-triggered immune responses in maize leaves inoculated with these mutants suggest that α-1,3-glucan does not play a role in masking of fungal cell walls and immune evasion, but rather controls mobility of fungal cell wall-modifying enzymes and cell wall integrity.
Lactobacillus crispatus dominance in the vaginal microbiome is associated with beneficial health outcomes, yet strain-level variation and its implications remain poorly understood. Here, we resolve the genomic context of three glycosyltransferase gene fragments (GT1-3) previously linked with dysbiotic states. Long-read resequencing revealed that GT1-3 are part of a ~18.7 kb Wzx/Wzy-dependent cell wall polysaccharide (CWPS) locus, containing several IS256-family transposases. Serial propagation in vitro produced isolates with 4.1 kb excised via a composite transposon encompassing the GT3, UDP-galactopyranose mutase, flippase, and hypothetical protein, demonstrating structural plasticity. Transmission electron microscopy showed a ~20%-25% thinner peptidoglycan layer in the derived strains, while FT-IR and monosaccharide analysis indicated no gross changes. Molecular dynamics simulations suggest that GT3 contributes to the structural stability of the glycosyltransferase complex, without compromising catalytic function. Together, these findings establish the CWPS locus as a mobile, structurally plastic element that directly influences cell wall architecture in L. crispatus.
The archaeal tubulin-like cytoskeletal protein CetZ1 is required for rod-cell morphogenesis during the development of motility in Haloferax volcanii. This is expected to improve swimming speed and directionality. Here, we found that deletion of cetZ1 or expression of a GTPase-defective mutant caused the expected defects in cell shape, and also resulted in a substantial defect in the assembly of the motility machinery, including the archaellum base marker protein ArlD1, the chemotaxis sensory array adapter CheW1, and signal transducer CheY. Interestingly, moderate overexpression of cetZ1 (by 2-3 fold) reduced motility and the assembly and polar placement of the motility machinery without detectably affecting the rod shape of motile cells. We also investigated deletion of the conserved paralog cetZ2, which caused no detected defects in swimming or rod shape. However, overexpression of cetZ2 caused mild hyper-motility, whereas the cetZ2 GTPase-defective mutant reduced motility; these effects were dependent on the presence of cetZ1, suggesting that the altered cetZ2 might interfere with CetZ1's role in motility. Finally, we saw that a functional CetZ1-mTurquoise2 fusion strongly localized at the poles of mature motile cells, where it partially co-localized with the motility machinery markers. Overall, our results suggest that roles of CetZ1 in cell shape or potentially the organisation and structure of the cell poles influence the polar assembly of the motility machinery.
