Comparing hormone dynamics in cereal crops via transient expression of hormone sensors.

Although hormone biology is critical for plant breeding, complex phenotypic outputs make it difficult to compare across species. We used transient expression of hormone biosensors and transcriptomics to simplify this output and quantify gibberellic acid (GA) and auxin responses across multiple cereal crop genotypes and tissues. We show the GPS2 biosensor detects exogenous GA in maize, barley, sorghum, and wheat. Measuring across GA dosages, we detect tissue- and genotype-specific differences in GA sensor response with an unexpected drop in GPS2 output in the maize d1 GA biosynthesis mutant after GA treatment, likely reflecting differences in GA response across samples. We used RNA sequencing followed by ortholog prediction and Gene Ontology-term enrichment analysis to measure GA responses in leaves and floral tissues from maize wildtype, d1, and barley Golden Promise. We determine that cross-tissue, cross-genotype, and cross-species GA responses include downregulation of GA-INSENSITIVE DWARF1 and upregulation of α-Expansin1, independent of GA biosynthesis. We identify F-Box proteins, hexokinase, and AMPK/SNF1 protein kinase orthologs as unexpected cross-species GA-responsive genes. We then compared transient expression of DR5, DR5v2, and DII-mDII auxin reporters in barley and maize and find DR5v2 and DII-mDII are functional auxin reporters in both species.