Maxwell Asiedu

University of Adelaide, United Kingdom

Abstract Title: Root Angle Variation in the Ozbarley Population is Driven by Genetic Variation in Key Expansin Genes

Biography:

Maxwell Asiedu is a joint PhD student between the University of Adelaide, Australia, and the University of Nottingham, UK. Maxwell completed his BSc in Agricultural Biotechnology at the Kwame Nkrumah University of Science and Technology (KNUST), Ghana. Subsequently, he pursued his MSc in Biotechnology (Plant Biotechnology pathway) at the University of Nottingham, funded by the prestigious Developing Solutions Masters Scholarship. His PhD research focuses on the genetic control of root angle variation in Australian barley germplasm, employing high-throughput phenotyping and genome-wide association studies (GWAS) to identify natural allelic variation contributing to the root system architecture. His work has uncovered novel expansin gene variants associated with shallow root angles, providing new insights into the molecular mechanisms underlying root development. Maxwell is passionate about plant genetics, crop improvement, and sustainable agriculture, with the long-term goal of contributing to the development of resilient crop varieties for global food security.

Research Interest:

Roots are essential for water and nutrient uptake and carbon sequestration. Steep root angles enhance access to deep soil water and nitrogen, while shallow angles favour topsoil resource capture. Root angle regulation involves several genes (Kirschner et al., 2024) (Kirschner et al., 2024). In barley, ENHANCED GRAVITROPISM1(EGT1) and ENHANCED GRAVITROPISM2 (EGT2) have been linked to root-angle control via cell wall mechanics (Fusi et al., 2022Fusi et al., 2022; Kirschner et al., n.d.Kirschner et al., 2021), though their downstream targets remain unknown. To explore this pathway, we used high-throughput phenotyping and genome-wide association studies (GWAS) on 214 diverse OzBarley lines. Haplotype analysis revealed no variants for EGT2 and eight EGT1 variants forming four haplotypes, none significantly associated with root angle phenotype (p > 0.1). However, GWAS identified a significant SNP (–log₁₀p = 6.16) on chromosome 1 within a gene encoding Expansin, a key cell wall-loosening protein (Cosgrove, 2000). Two protein-coding variants for this expansin were found: a missense mutation and a stop-gained mutation. Both alleles were significantly associated with shallow root angles compared to wild type (p < 0.05), consistent with haplotype data (p < 0.05). The stop-gained allele truncates the NC-terminal domain of the Expansin protein, while AlphaFold modelling predicts the missense variant also disrupts protein function. These findings suggest that natural variation in Expansin contributes to root angle variation in the OzBarley panel and support the model in which EGT1 (and EGT2) regulate wall extensibility by modulating enzymes like Expansin. Functional validation through CRISPR knockouts and TILLING mutant screens in barley and other species could help validate the functional impact of Expansin.