Osiris-Exploring the Yield Potential of Novel Spike Architecture in Hexaploid Wheat By Genome Wide Association Mapping and Targeted Mutagenesis Using RNA-Guided Cas Endonucleases

Grain number, measurable as per unit area, per plant, or per spike is an important yield component of wheat. Further enhancement in grain number per plant may be possible through modifying the inflorescence architecture of the spike by increasing reproductive sink tissues, and thus, more potential grain sites. Wheat and barley mutants that display non-canonical spike-branching have been characterized in our laboratory of which one tetraploid wheat mutant, ‘Miracle Wheat’ (i.e. branched head, bh^t), produced significantly more grains per spike that consequently led to higher spike yield. Moreover, we positionally cloned and identified mutant alleles of two other spike architecture genes, compositum 1 (com1) and Six-rowed spike 4 (Vrs4) in barley, that resulted in branch formation. Therefore, the three above-mentioned genes—Com1, bh^t, Vrs4—represent exciting targets for engineering novel spike architecture in hexaploid wheat to potentially produce more spikelets and subsequently more grains per spike. To this end, we aim to employ genome engineering technology, namely CRISPR/Cas9, to knock-out these three negative regulators of spike-branching in hexaploid wheat to generate mutant plants with improved seed number or sink capacity. To overcome the known trade-off effect between seed number and seed size/weight, we will perform strategic crossings between novel sink-elevated, branched-spike genotypes (obtained through CRISPR/Cas9) and genotypes carrying resource-efficient and/or large-seeded related QTLs. The genotypes carrying genetic determinants of large-seeds will be discovered by exploring the existing natural genetic variation for grain size/weight in a diverse bread wheat germplasm pool following a Genome Wide Association Scan (GWAS) and mapping approach.