Biology subjects

Haslam, T. M.

Publications and source records attributed to Haslam, T. M..

3 recordsLinked to original sources

bioRxiv2025

Identification of INOSITOL PHOSPHORYLCERAMIDE SYNTHASE 2 (IPCS2) as a new rate-limiting component in Arabidopsis pathogen entry control

SIGNIFICANCE STATEMENTPolarized transport of executive defense gene products to sites of attempted microbial invasion is important for plant pathogen entry control and disease resistance. Here, we provide evidence that INOSITOL PHOSPHORYLCERAMIDE SYNTHASE 2 (IPCS2)-dependent sphingolipid production contributes to the role of the trans-Golgi network as a multi-domain sorting compartment, and mediates proper delivery of an ATP-binding cassette transporter to polarized plasma membrane domains at plant-microbe interaction sites. INOSITOL PHOSPHORYLCERAMIDE SYNTHASE 2 (IPCS2) is involved in the biosynthesis of complex sphingolipids at the trans-Golgi network (TGN). Here, we demonstrate a role of IPCS2 in penetration resistance against non-adapted powdery mildew fungi. A novel ipcs2W205* mutant was recovered from a forward genetic screen for Arabidopsis plants with enhanced epidermal cell entry success of the non-adapted barley fungus Blumeria graminis f. sp. hordei (Bgh). A yeast complementation assay and a sphingolipidomic approach revealed that the ipcs2W205* mutant represents a knock-out and lacks IPCS2-specific enzymatic activity. Further mutant analyses suggested that IPCS2-derived glycosyl inositol phosphorylceramides (GIPCs) are required for cell entry control of non-adapted fungal intruders. Confocal laser scanning microscopy (CLSM) studies indicated that upon pathogen attack, IPCS2 remains at the TGN to produce GIPCs, while focal accumulation of the defense cargo PENETRATION 3 (PEN3) at Bgh penetration sites was reduced in the ipcs2W205* mutant background. Thus, we propose a model in which sorting events at the TGN are facilitated by complex sphingolipids, regulating polar secretion of PEN3 to host-pathogen contact sites to terminate fungal ingress.

plant biology↗

bioRxiv2024

Complex sphingolipids are essential for cell division and plasmodesmal development in the moss Physcomitrium patens

Developmental patterning and organ structure are elegantly simple in the moss Physcomitrium patens. In molecular genetic studies, this facilitates both the cultivation of severe mutant alleles and their phenotypic characterization. Essential membrane lipids, such as complex phosphosphingolipids (in plants, glycosyl inositol phosphorylceramides, GIPCs), have been difficult to functionally characterize due to non-viable and pleiotropic phenotypes of mutants affected in their synthesis in Arabidopsis thaliana. Following the isolation and biochemical characterization of mutants affected in GIPC synthesis in P. patens, including sphinganine-C4-hydroxylase (s4h/sbh) and inositol phosphorylceramide synthase (ipcs), we now report some of their morphological, histological, and cytological phenotypes. We observed alteration in cell division, expansion, and differentiation. Specifically, the s4h knock-out mutant had abnormal cell division planes, as well as irregular depositions attached to cell walls. Severe ipcs mutant alleles showed frequent incomplete cell divisions, causing compromised cell autonomy as demonstrated by intercellular motility assays. These phenotypes suggest that sphingolipids impact both the orientation and proper formation of the cell plate during cytokinesis. Transmission electron microscopy revealed dramatic plasmodesmal structural defects in all three mutants, however, qualitative aspects of plasmodesmal transport do not seem to be severely impacted. Our methods can be used as a toolkit for quantifying growth, and specifically cell division and plasmodesmal phenotypes in mosses; our present results elucidate the specific contributions of GIPCs to fundamental cell functions. Finally, the severity of the observed defects in cell functions and ultrastructure highlight the resilience and utility of P. patens for studying basic cellular functions and severe mutant phenotypes.

plant biology↗

bioRxiv2023

Viable mutants of essential genes in Physcomitrium patens as tools for studying primary metabolic processes

Sphingolipids are essential components of plant cells, which have been notoriously difficult to study in part due to pleiotropic or lethal knock-out mutant phenotypes. By relying on alternative end-joining of double stranded breaks, we successfully used CRISPR/Cas9 mutagenesis to generate a population of diverse, viable mutant alleles of genes required for sphingolipid assembly in totipotent protoplasts of the moss Physcomitrium patens. We targeted the INOSITOL PHOSPHORYLCERAMIDE SYNTHASE (IPCS) gene family, which catalyzes the committed step in the synthesis of glycosyl inositol phosphorylceramides (GIPCs), the most abundant class of sphingolipids found in plants. We isolated knock-out single mutants and knock-down higher-order mutants showing a spectrum of deficiencies in GIPC content. Remarkably, we also identified two mutant alleles accumulating inositol phosphorylceramides, the direct products of IPCS activity, and provide our best explanation for this unexpected phenotype. Our approach is broadly applicable for studying essential genes and gene families, and for obtaining unusual lesions within a gene of interest.

plant biology↗