Comparative transcriptomics pinpoints conserved and specific transcriptional responses to phosphorus limitation.

Translating biological knowledge from Arabidopsis to crop species is important to advance agriculture and secure food production in the face of dwindling fertilizer resources and biotic and abiotic stresses. However, it is often not trivial to identify functional homologs (orthologs) of Arabidopsis genes in crops. Combining sequence and expression data can improve the correct prediction of orthologs. Here, we conducted a large-scale RNA sequencing based transcriptomics study of Arabidopsis, Medicago, Brachypodium, and Setaria grown side-by-side in phosphorus (P)-sufficient and P-limited conditions to generate comparable transcriptomics datasets. Comparison of top 200 P-limitation-induced genes in Arabidopsis revealed that ~80% of these genes have identifiable close homologs in the other three species but only ~50% retain their P-limitation response in the legume and grasses. Most of the hallmark genes of the P-starvation response were found conserved in all four species. This study reveals many known, novel, unannotated, conserved, and species-specific forms of regulation of the transcriptional P-starvation response. Identification and experimental verification of expressologs by independent RT-qPCR for P-limitation marker genes in Prunus showed the usefulness of comparative transcriptomics in pinpointing the functional orthologs in diverse crop species. This study provides an unprecedented resource for functional genomics and translational research to create P-efficient crops.