Biology subjects

Mueller, K.-K.

Publications and source records attributed to Mueller, K.-K..

4 recordsLinked to original sources

bioRxiv2025

New insights into bryophyte arabinogalactan-proteins from a hornwort and a moss model organism

Two bryophyte models, the hornwort Anthoceros agrestis (Anthoceros) and the moss Physcomitrium patens (Physcomitrium), were analysed for presence of arabinogalactan-proteins (AGPs), as emergence of these signalling glycoproteins in evolution is still under debate. AGPs of both species had a galactan core structure similar to that of other bryophyte and fern AGPs, but different to angiosperm AGPs, as 1,6-linked pyranosidic galactose was almost absent. In the Physcomitrium AGP, furanosidic arabinose (Araf) linkages were mainly terminal (10 %) or 5-linked (13 %), while in Anthoceros, terminal Araf dominated (26 %) and was accompanied by very low amounts of 1,3-Araf and pyranosidic terminal Ara. Unusual 3-O-methylated pyranosidic rhamnose, which has never been detected in cell walls of angiosperms, occurred in both bryophyte AGPs (5 % in Anthoceros, 10 % in Physcomitrium AGP), This was comparable to AGPs of other spore-producing land plants. Bioinformatic search in genomes of 14 bryophyte species revealed that most hornworts lack sequences encoding GPI-anchored classical AGPs. Generally, hornworts contained less sequences for AGP protein backbones compared to the liverwort Marchantia polymorpha and the moss Physcomitrium patens. All of them comprise sequences for chimeric AGPs, and among those surprisingly xylogen-like AGPs. Homologous sequences encoding glycosyltransferases and other enzymes involved in the synthesis and decoration of the AGP galactan framework were present in all bryophyte genomes. Immunocytochemistry of Anthoceros tissue detected AGPs at the plasma membrane/cell wall interface but also at vacuolar and vesicle membranes, suggesting new functions of AGPs in bryophytes. SIGNIFICANCE STATEMENTExtant bryophytes are key to infer evolution of the most recent common ancestor of all land plants. As cell walls were important for adaptation to life on land, we analysed arabinogalactan-proteins from the hornwort Anthoceros agrestis and the moss Physcomitrium patens and detected terminal 3-O-methylrhamnose residues, which also occur in fern AGPs but not in angiosperms. Bioinformatic search for AGP protein backbones and glycosyltransferases in bryophyte genomes further strengthens understanding of AGP evolution during terrestrialization.

plant biology↗

bioRxiv2025

Synthetic and plant-derived multivalent galactans as modulators of cancer-associated galectins-3 and -9

Galectins are {beta}-galactoside-binding proteins with numerous functions. Some of them are involved in proliferation and metastasis of cancer, making them promising therapeutic targets. As different plant glycans have been shown to bind to galectins, plant saccharides might be potential galectin inhibitors. To produce plant galactans rich in galactose and smaller in size, we degraded arabinogalactan-proteins from Echinacea purpurea and Zostera marina as well as arabinogalactan from larch. As galectin (Gal)-3 and -9 both have been described to be involved in cancer development, we quantified the binding capacities of the different galactans to both galectins by biolayer-interferometry. Our results revealed that all plant-derived galactans and Yariv reagents with terminal galactose and lactose residues bind to Gal-3 in micromolar ranges. Surprisingly, only the higher charged galactans from Zostera marina showed affinity to Gal-9. Investigations of two different pancreatic cancer cell lines (Panc1 and Panc89) and different cell variants thereof revealed that Gal-3 was expressed by both cell lines with a significantly higher Gal-3 level in Panc1 cells compared to Panc89 cells. Conversely, Gal-9 was only detected in Panc89 cells. The findings revealed that galactans are promising sources to develop galectin antagonists and plant galactans from different species express specificities for distinct galectins.

cancer biology↗

bioRxiv2023

The cell walls of different Chara species (Charophyceae) are characterized by branched galactans rich in 3-O-methylgalactose and absence of arabinogalactan-proteins

Streptophyte algae are the closest relatives of land plants and their latest common ancestor performed the most drastic adaptation that happened in plant evolution around 500 million years ago: the conquest of land. Beside other adaptations, this step required changes in cell wall composition. Today knowledge on cell walls of streptophyte algae and especially presence of arabinogalactan-proteins (AGPs), which are important signaling molecules of all land plants, is limited. To get deeper insights in cell walls of streptophyte algae, especially of the Charophyceae, we performed sequential cell wall extractions of four Chara species. The three species Chara globularis, Chara subspinosa and Chara tomentosa revealed comparable cell wall compositions with pectins, xylans and xyloglucans, whereas Chara aspera was outstanding with higher amounts of uronic acids in the pectic fractions and lack of reactivity with antibodies binding to xylan- and xyloglucan epitopes. Search for AGPs in the four Chara species and also Nitellopsis obtusa revealed presence of galactans with pyranosidic galactose in 1,3-, 1,6- and 1,3,6-linkage, which are typical galactan motifs of land plant AGPs. A unique feature of these branched galactans were high portions of 3-O-methylgalactose. Only Nitellopsis contained substantial amounts of Ara. Bioinformatic search for prolyl-4-hydroxylase necessary for biosynthesis of AGPs revealed one possible functional sequence in the genome of Chara braunii, but no hydroxyproline could be detected in the four Chara species and Nitellopsis obtusa. We conclude that AGPs typical for land plants are absent at least in these members of the Charophyceae.

plant biology↗

bioRxiv2022

Fern cell walls and the evolution of arabinogalactan-proteins in streptophytes

Significant changes have occurred in plant cell wall composition during evolution and diversification of tracheophytes. As the sister lineage to seed plants, knowledge on the cell wall of ferns is key to track evolutionary changes across tracheophytes and to understand seed plant-specific evolutionary innovations. Fern cell wall composition is not fully understood, including limited knowledge of glycoproteins such as the fern arabinogalactan-proteins (AGPs). Here, we characterize the AGPs from the leptosporangiate fern genera Azolla, Salvinia and Ceratopteris. The carbohydrate moiety of seed plant AGPs consists of a galactan backbone including mainly 1,3- and 1,3,6-linked pyranosidic galactose, which is conserved across the investigated fern AGPs. Yet, unlike AGPs of angiosperms, those of ferns contained the unusual sugar 3-O-methylrhamnose. Besides terminal furanosidic Ara (Araf), the main linkage type of Araf in the ferns was 1,2-linked Araf, whereas in seed plants 1,5-linked Araf is often dominating. Antibodies directed against carbohydrate epitopes of AGPs supported the structural differences between AGPs of ferns and seed plants. Comparison of AGP linkage types across the streptophyte lineage showed that angiosperms have rather conserved monosaccharide linkage types; by contrast bryophytes, ferns and gymnosperms showed more variability. Phylogenetic analyses of glycosyltransferases involved in AGP biosynthesis and bioinformatic search for AGP protein backbones revealed a versatile genetic toolkit for AGP complexity in ferns. Our data reveal important differences across AGP diversity which functional significance is unknown. This diversity sheds light on the evolution of the hallmark feature of tracheophytes: their elaborate cell walls. SIGNIFICANCE STATEMENTFerns are the sister lineage of seed plants and key to understanding plant evolution. To understand ferns unique cell walls, we analysed arabinogalactan-proteins from the fern genera Azolla, Salvinia and Ceratopteris. Comparison of AGP structures throughout the streptophyte lineage reveals special features in relation to systematic positions and proposes a trend to more hydrophilic AGPs in course of evolution. Through comparative genomic analyses, we pinpoint the potential genetic players for this diversity in cell walls.

plant biology↗