Biology subjects

Johansen, K.

Publications and source records attributed to Johansen, K..

2 recordsLinked to original sources

bioRxiv2026

NMR assignment and functional characterization of biotechnologically modified xanthan

Xanthan gum is one of the most important industrial microbial polysaccharides, yet comprehensive molecular-level structural characterization remains limited because of its high molecular weight, conformational rigidity, and severe spectral overlap in nuclear magnetic resonance spectroscopy. Here, we present a near-complete 1H/13C NMR chemical shift assignment of the xanthan repeating unit by combining multidimensional NMR spectroscopy with targeted glycosyltransferase knockout strains and controlled enzymatic depolymerization. Comparative analysis of wild-type xanthan and{Delta} gumI and{Delta} gumK variants enabled the unambiguous assignment of {beta}-mannose and glucuronic acid resonances, and, by extension, of the remaining sugars, supporting future structural studies of engineered xanthan variants. In addition, we investigated how side-chain composition affects xanthan properties by analyzing genetically modified variants lacking specific acetyl, pyruvyl, or sugar residues. Temperature-dependent 1H NMR determined order-disorder transition temperatures and revealed that removing pyruvate or negatively charged side-chain components increased thermal stability, whereas losing the terminal {beta}-mannose destabilized the ordered conformation. Together, these results establish a robust NMR assignment for xanthan and provide new insights into how individual side-chain substituents influence the structural stability of this polysaccharide, facilitating the rational characterization of engineered xanthan variants and structurally closely related polysaccharides.

biochemistry↗

bioRxiv2023

Deciphering Salt Stress Responses in Solanum pimpinellifolium through High-Throughput Phenotyping.

Soil salinity is a major environmental stressor affecting agricultural productivity worldwide. Understanding plant responses to salt stress is crucial for developing resilient crop varieties. Wild relatives of cultivated crops, such as wild tomato, Solanum pimpinellifolium, can serve as a useful resource to further expand the resilience potential of the cultivated germplasm, S. lycopersicum. In this study, we employed high-throughput phenotyping in the greenhouse and field conditions to explore salt stress responses of a S. pimpinellifolium diversity panel. Our study revealed extensive phenotypic variations in response to salt stress, with traits such as transpiration rate, shoot mass, and ion accumulation showing significant correlations with plant performance. We found that while transpiration was a key determinant of plant performance in the greenhouse, shoot mass strongly correlated with yield under field conditions. Conversely, ion accumulation was the least influential factor under greenhouse conditions. Through a Genome Wide Association Study, we identified candidate genes not previously associated with salt stress, highlighting the power of high-throughput phenotyping in uncovering novel aspects of plant stress responses. This study contributes to our understanding of salt stress tolerance in S. pimpinellifolium and lays the groundwork for further investigations into the genetic basis of these traits, ultimately informing breeding efforts for salinity tolerance in tomato and other crops.

plant biology↗