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Keywords:

  • Pi starvation;
  • local response;
  • systemic response;
  • transcriptomic;
  • Arabidopsis

Summary

Phosphate is a crucial and often limiting nutrient for plant growth. To obtain inorganic phosphate (Pi), which is very insoluble, and is heterogeneously distributed in the soil, plants have evolved a complex network of morphological and biochemical processes. These processes are controlled by a regulatory system triggered by Pi concentration, not only present in the medium (external Pi), but also inside plant cells (internal Pi). A ‘split-root’ assay was performed to mimic a heterogeneous environment, after which a transcriptomic analysis identified groups of genes either locally or systemically regulated by Pi starvation at the transcriptional level. These groups revealed coordinated regulations for various functions associated with Pi starvation (including Pi uptake, Pi recovery, lipid metabolism, and metal uptake), and distinct roles for members in gene families. Genetic tools and physiological analyses revealed that genes that are locally regulated appear to be modulated mostly by root development independently of the internal Pi content. By contrast, internal Pi was essential to promote the activation of systemic regulation. Reducing the flow of Pi had no effect on the systemic response, suggesting that a secondary signal, independent of Pi, could be involved in the response. Furthermore, our results display a direct role for the transcription factor PHR1, as genes systemically controlled by low Pi have promoters enriched with P1BS motif (PHR1-binding sequences). These data detail various regulatory systems regarding Pi starvation responses (systemic versus local, and internal versus external Pi), and provide tools to analyze and classify the effects of Pi starvation on plant physiology.