The Allele of Conditions Misregulation of the Phosphorus Starvation Response in Maize ( Ssp. L.)

Plant PHO1 proteins play a central role in the translocation and sensing of inorganic phosphate. The maize ( ssp. ) genome encodes two co-orthologs of the gene, designated and . Here, we report the characterization of the transposon footprint allele , which we refer to hereafter as . The allele is a stable derivative formed by excision of an transposable element from the gene. The allele contains an 8-bp insertion at the point of transposon excision that disrupts the reading frame and is predicted to generate a premature translational stop. We show that the allele is linked to a dosage-dependent reduction in transcript accumulation and a mild reduction in seedling growth. Characterization of shoot and root transcriptomes under full nutrient, low nitrogen, low phosphorus, and combined low nitrogen and low phosphorus conditions identified 1100 differentially expressed genes between wild-type plants and plants carrying the mutation. Of these 1100 genes, 966 were upregulated in plants carrying , indicating the wild-type PHO1;2a to predominantly impact negative gene regulation. Gene set enrichment analysis of the -misregulated genes revealed associations with phytohormone signaling and the phosphate starvation response. In roots, differential expression was broadly consistent across all nutrient conditions. In leaves, differential expression was largely specific to low phosphorus and combined low nitrogen and low phosphorus conditions. Of 276 genes upregulated in the leaves of mutants in the low phosphorus condition, 153 were themselves induced in wild-type plants with respect to the full nutrient condition. Our observations suggest that functions in the fine-tuning of the transcriptional response to phosphate starvation through maintenance and/or sensing of plant phosphate status.