Root Pulling Force Across Drought in Maize Reveals Genotype by Environment Interactions and Phosphate Transporter 1-2a as a Candidate Gene
Authors: Patrick Woods; Jack Mullen; Kirsten Hein; John McKay
Affiliation: Colorado State University
Keywords: Complex traits
High-throughput, field-based characterization of root systems for hundreds of genotypes in thousands of plots is necessary for breeding and identifying loci underlying variation in root traits and their plasticity. We designed a large-scale sampling of root pulling force (RPF), the vertical force required to extract the root system from the soil, in a maize diversity panel under differing irrigation levels for two growing seasons. We then characterized the root system architecture of the extracted root crowns. We found consistent patterns of phenotypic plasticity for RPF for a subset of genotypes under differential irrigation, suggesting that root plasticity is predictable. Using genome-wide association analysis (GWAS), we identified 54 SNPs as statistically significant for six independent RPF measurements across two irrigation levels and four developmental timepoints. One interesting candidate gene identified for RPF under irrigated treatments was Phosphate Transporter 1-2a (PHO1-2a), a gene involved in phosphate transfer from the root to the shoot via the root stele. To functionally validate the effect of PHO1-2a on RPF we are conducting both screens of PHO1-2a mutants, and quantitative trait loci (QTL) mapping in a recombinant inbred line (RIL) population created from two closely related iodent maize lines (PH207 and L127) which possess the alternate alleles at the PHO1-2a SNP identified in the GWAS. Comparisons of RPF between mature field grown wild-type and one allele of PHO1-2a mutant plants during the 2021 field season show significant differences (p < 0.05) across numerous root system traits including RPF, root mass, and root area suggesting a true role of PHO1-2a in determining root architectural phenotypes. Root phenotypes of additional mutant alleles of PHO1-2a and the PH207 x L127 RIL population will be analyzed in the 2022 field season for further characterization of this gene’s effect on root system architecture in maize.