Phosphate Starvation Root Architecture and Anthocyanin Accumulation Responses Are Modulated by the Gibberellin-DELLA Signaling Pathway in Arabidopsis

Phosphate (Pi) is a macronutrient that is essential for plant growth and development. However, the low mobility of Pi impedes uptake, thus reducing availability. Accordingly, plants have developed physiological strategies to cope with low Pi availability. Here, we report that the characteristic Arabidopsis thaliana Pi starvation responses are in part dependent on the activity of the nuclear growth-repressing DELLA proteins (DELLAs), core components of the gibberellin (GA)-signaling pathway. We first show that multiple shoot and root Pi starvation responses can be repressed by exogenous GA or by mutations conferring a substantial reduction in DELLA function. In contrast, mutants having enhanced DELLA function exhibit enhanced Pi starvation responses. We also show that Pi deficiency promotes the accumulation of a green fluorescent protein-tagged DELLA (GFP-RGA repressor of ga1-3) in root cell nuclei. In further experiments, we show that Pi starvation causes a decrease in the level of bioactive GA and associated changes in the levels of gene transcripts encoding enzymes of GA metabolism. Finally, we show that the GA-DELLA system regulates the increased root hair length that is characteristic of Pi starvation. In conclusion, our results indicate that DELLA-mediated signaling contributes to the anthocyanin accumulation and root architecture changes characteristic of Pi starvation responses, but do not regulate Pi starvation-induced changes in Pi uptake efficiency or the accumulation of selected Pi starvation-responsive gene transcripts. Pi starvation causes a reduction in bioactive GA level, which, in turn, causes DELLA accumulation, thus modulating several adaptively significant plant Pi starvation responses.