With the exception of root hair development, the role of the phytohormone ethylene is not clear in other aspects of plant responses to inorganic phosphate (Pi) starvation. The induction of AtPT2 was used as a marker to find novel signalling components involved in plant responses to Pi starvation. Using genetic and chemical approaches, we examined the role of ethylene in the regulation of plant responses to Pi starvation. hps2, an Arabidopsis mutant with enhanced sensitivity to Pi starvation, was identified and found to be a new allele of CTR1 that is a key negative regulator of ethylene responses. 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, increases plant sensitivity to Pi starvation, whereas the ethylene perception inhibitor Ag+ suppresses this response. The Pi starvation-induced gene expression and acid phosphatase activity are also enhanced in the hps2 mutant, but suppressed in the ethylene-insensitive mutant ein2-5. By contrast, we found that ethylene signalling plays a negative role in Pi starvation-induced anthocyanin production. These findings extend the roles of ethylene in the regulation of plant responses to Pi starvation and will help us to gain a better understanding of the molecular mechanism underlying these responses. © 2010 The Authors. New Phytologist © 2010 New Phytologist Trust.
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