Mohnen, D. | Search bioRxiv

bioRxiv2026

Switchgrass Root Cell Wall Composition and Anatomy Vary with Depth, Suggesting Approaches for Trait Enhancement

Plant root cellular architecture and cell wall composition influence plant productivity, stress resilience, biotic interactions, and potentially soil carbon accumulation. This study establishes comprehensive compositional parameters for roots of a lowland switchgrass genotype, DVR3. Root traits were analyzed in 12.5 cm depth segments, from Zone 1 near the surface to Zone 4 down to 50 cm. Mean abundance (g/mg) for major cell wall components included cellulose 470 {+/-} 20, xylose 250 {+/-} 20, lignin 170 {+/-} 15, and total suberin 35 {+/-} 5. Composition and cellular anatomy varied with depth, in a partially coordinated manner. Cross sections showed extensive aerenchyma in mature root regions despite greater root mass density, corresponding to abundant lignin and cellulose. Deep roots were enriched for pectin-associated traits, including arabinogalactan II, homogalacturonan, and arabinose-associated linkages. Suberin content did not vary significantly, though Casparian strip formation, endoderm and exoderm thickening, and suberin surface staining progressed with development. Similar trends in root lignin and specific root length were observed for another lowland switchgrass genotype, AP13. These results suggest that it may be possible to genetically enhance native switchgrass root chemistry to promote soil penetration and below-ground carbon accumulation by reducing variability with development, potentially via cell-type specific adjustments.

plant biology↗

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↗