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Is the phosphate analogue phosphite interfering with plant phosphorus homeostasis and signalling?

Jost, R., Pharmawati, M., Berkowitz, O., Pearse, S.J., Lambers, H. and Finnegan, P.M. (2011) Is the phosphate analogue phosphite interfering with plant phosphorus homeostasis and signalling? In: XVIII International Botanical Congress IBC2011, 23 - 30 July, Melbourne, Australia.

Abstract

Phosphorus (P) is a macronutrient that is essential for plant growth, but often has a low availability due to a low solution P pool and sorption to soil minerals. P is taken up by the roots of plants in the form of inorganic phosphate (Pi) and plants feature complex regulatory networks to maintain P homeostasis and optimise their Pi uptake and storage capacities to meet metabolic and developmental demand. Phosphite (Phi, HPO32-) is a more reduced form of P that is used as a biostat to enhance plant resistance against Phytophthora species. These pathogenic oomycetes are a major threat to both food security (Phytophthora infestans caused the Irish potato famine in the mid 19th century) and natural diversity (Phytophthora cinnamomi has been termed the ‘biological bulldozer’ due to its devastating effect on plant communities in many biodiversity hotspots around the globe). However, despite its successful marketing as a ‘fungicide’ relatively little is known about its longer-term impact on plant growth and development. Phi is believed to mimic Pi in suppressing the plant’s Pi-starvation response and severely inhibits growth of plants with a low P status. Its uptake most likely proceeds via transporters of the PHT1 family and is highly sensitive to competitive inhibition by Pi. Here we show that Phi is not a perfect mimetic of Pi in suppressing Pi-starvation responses. While it does suppress root-hair formation and attenuate the expression of many Pi-starvation-induced genes, it does not reduce the expression of many other well known Pi-signalling genes. In contrast to Pi resupply, Phi addition actually leads to a severe inhibition of primary and secondary root elongation and an increase in lateral root density that is much more pronounced than under Pi starvation itself. Anthocyanin accumulation in older leaves is not completely reversed by supplying Phi instead of Pi to P-starved plants. This could be an indication for altered shoot Pi reallocation patterns in those plants. We show that Phi evokes a set of distinct physiological and molecular reactions that distinguish it from well characterised Pi-induced changes and therefore make it an excellent tool to study P-sensing and -signal-transduction pathways. This will also provide new insights into how Phi alters plant defence responses to boost their resistance against parasitic oomycetes.

Publication Type: Conference Item
Murdoch Affiliation: Centre for Phytophthora Science and Management
School of Biological Sciences and Biotechnology
URI: http://researchrepository.murdoch.edu.au/id/eprint/19995
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