Biology subjects

Black, I. M.

Publications and source records attributed to Black, I. M..

3 recordsLinked to original sources

bioRxiv2026

Ctenophore mesoglea: building a mucus-like body

Ctenophora are one of the earliest, if not the earliest branching animal, making them crucial for insight into the early events of metazoan evolution. Ctenophores are largely composed of an extracellular mesoglea, but they lack homologs for the fibrous collagens that form a typical metazoan extracellular matrix (ECM). Therefore, the nature of this body-dominating material and its physiological role remains unknown. We found that ctenophore mesoglea is dominated by mucin-related proteins and novel sulfated polysaccharides. Mucus-like material that functions as an internal skeleton rather than as an external secretion indicates fundamental differences in epithelial function and ECM physiology between ctenophores and other Metazoa, suggesting an early period of biochemical and biomechanical diversity prior to the innovation of elastic connective tissue.

biochemistry↗

bioRxiv2025

Arabidopsis GALACTURONOSYLTRANSFERASE (GAUT) 1 synthesizes a homogalacturonan tightly bound to the cell wall and required for cell expansion

Arabidopsis GALACTURONOSYLTRANSFERASE1 (GAUT1) synthesizes homogalacturonan (HG), the most abundant pectin in growing plant cells. GAUT1 has the greatest in vitro enzyme activity of the six confirmed Arabidopsis HG biosynthetic GAUTs, but its biological activity remains elusive. Here we show that Arabidopsis GAUT1 homozygous mutants have a severe dwarfed seedling phenotype, survive several weeks as 2 to 3 mm seedlings, and have severely reduced shoot and root growth and hypocotyl epidermal, cortex and endodermal cell size. gaut1-1 pollen tubes are shorter than WT with increased bursting. Complementation of homozygous gaut1-1 with GAUT1 coding sequence driven by the GAUT1 promoter restored WT-like growth. The extreme dwarf phenotype of homozygous gaut1-1 seedlings precluded their use for detailed cell wall analysis, thus suspensions cultures were produced from callus generated from mutant and WT seedlings. Homozygous gaut1-1 suspension cells were smaller than WT with [~]30% reduced wall GalA content compared to WT. Sequential extraction of the walls with increasingly harsh solvents and sugar composition analysis revealed reduced GalA content in only the 4M KOH post-chlorite fraction, indicating that GAUT1-synthesized HG was held tightly in the wall by direct or indirect hydrogen bonding and/or oxidation-sensitive linkages. Treatment of wall fractions with endopolygalacturonase to hydrolyze HG and gel electrophoretic separation of hydrolysates exposed an HG-associated doublet band markedly downregulated in the homozygous gaut1-1 4M KOH post-chlorite fraction and to a lesser extent in 4M KOH and sodium chlorite fractions. NMR analysis identified the band as rhamnogalacturonan (RG)-II. Super resolution microscopy using anti-HG antibodies showed that, compared to WT, the homozygous gaut1-1 hypocotyl epidermal and callus cells had reduced content and length of HG nanofilaments, HG fibers associated with cell expansion in Arabidopsis. The results demonstrate that GAUT1-synthesized HG resides in a tightly-cell-wall-bound, RG-II-containing polymer required for HG nanofilament formation and seedling cell expansion.

plant biology↗

bioRxiv2024

Deep structural analysis of rhamnogalacturonan-I (RG-I) in Arabidopsis reveals new insights into pectin diversity

Pectic polysaccharides are an integral part of primary plant cell walls, where they are perfrom crucial structural and biological functions. Pectin is generally divided into four distinct structural categories, including homogalacturonan, xylogalacturonan, rhamnogalacturonan I (RG-I) and rhamnogalacturonan II. Among the four main pectin domains, the structural intricacies of rhamnogalacturonan-I (RG-I) remain the least understood, especially in widely employed plant models. We employed multiple complementary analytical techniques to present a detailed structural analysis of RG-I in the model system Arabidopsis thaliana. Using highly purified RG-I from different tissues, we conducted comparative linkage and NMR analyses, complemented by mass spectrometry of enzymatically digested RG-I oligosaccharides. Our findings present the most comprehensive structural overview of Arabidopsis RG-I to date, revealing novel structural features. Notably, we identified O-acetylation of rhamnose backbone residues as a predominant feature, a modification previously unreported in this species. The combined results present a comprehensive structural overview of Arabidopsis thaliana RG-I that will serve as a roadmap for studying pectin biosynthesis and function.

biochemistry↗