Molecular dissection of the phospate signalling network in Arabidopsis thaliana

[Truncated abstract] Significant progress has been made in identifying the genetic components involved in the complex adaptive strategies of plants to Pi starvation, understanding the regulation of Pi signalling and comprehending the cross-talk between P and other nutrients and hormones. However, there are still many knowledge gaps regarding the function of the components in the Pi sensing and signalling pathway in plants. This PhD project found that GLYCINE RICH RNA-BINDING PROTEIN 8 (AtGRP8) is a novel molecular regulator involved in Pi homeostasis and determined that independent loss of several PHOSPHATE TRANSPORTER 1 (PHT1) genes causes mis-regulation of some aspects of the Pi starvation response in Arabidopsis. AtGRP8 is known to play a role in post-transcriptional regulation in response to several environmental conditions that are often associated with changes in plant Pi status. AtGRP8 transcript abundance was found to be induced during Pi deprivation, with Pi status-dependent modulation of the relative abundance of the alternatively spliced transcripts. This is the first study to link the modulation of splice variant abundance to a response to nutrient deficiency. Additionally, two new AtGRP8 splice variants induced in cell cultures during Pi limitation were identified. Examination of Atgrp8 mutants indicated that the AtGRP8 protein is most likely a negative regulator of the adaptive machinery necessary to maintain Pi homeostasis. The phenotype of Atgrp8 mutants resembles those in pdr2 and siz1 mutant lines suggesting a role in the same genetic pathway as PRD2 and/or SIZ1. PHT1;1 is a major Pi transporter in Arabidopsis roots.