Hazel Gaza1, Ricarda Jost1, Martha Ludwig2 and Patrick Finnegan1 Arabidopsis glycine-rich RNA binding protein 8 (AtGRP8) transcript abundance increases in response to phosphate starvation Hazel Gaza1, Ricarda Jost1, Martha Ludwig2 and Patrick Finnegan1 1School of Plant Biology, 2 School of Biomedical, Biomolecular and Chemical Science, The University of Western Australia, Crawley, Western Australia INTRODUCTION Plant growth and development is restricted by phosphate (Pi). This leads to a physiological response through altering gene expression and metabolism. The expression of the Arabidopsis glycine-rich RNA-binding protein 8 (AtGRP8) gene is regulated by a number of external stimuli including cold, circadian rhythm, abscissic acid, drought and salinity (Carpenter et al., 1994; Kwak et al, 2005). The altered expression of AtGRP8 under different stress conditions and an on-going interest in Pi starvation responses led us to test whether this gene may also be involved in the adaptive response to this stress. EXPERIMENT 1 EXPERIMENT 2 Col-0 plants grown under limiting Pi conditions showed retardation of the primary root growth and increased root hair formation compared to controls, both typical Pi starvation responses. The Atgrp8-1 knock-out line and Col-3, the corresponding wild-type, were grown on medium with 250 μM Pi or with 5 μM Pi . Atgrp8-1 T- DNA 5’UTR Promoter region EXON1: 108bp EXON2: 402bp Intron: 283bp + P Pi content of roots and shoots. - P mRNA from roots and shoots was isolated and used to make cDNA using the oligo(dT)-coated magnetic beads. Pi content in roots [mmol / g FW] 3 5 7 3 5 7 Col-3 Atgrp8-1 Days AtGRP8 is not involved in the regulation of Pi content in the roots and shoots. Quantitative real-time PCR, using ACT7, PDF2 and YLS8 as reference genes, was conducted to determine the transcript profile of AtGRP8. Root elongation rates were determined by marking the position of the root tip daily. Col-3 wild-type roots have a higher growth rate on Pi-sufficient medium than those of Atgrp8-1. Both lines have the same root growth rate on Pi-deficient medium (not shown). 1 3 5 7 Days 1 3 5 7 Days AtGRP8 transcript abundance increased by 2-fold in the roots of Pi- starved plants. AtGRP8 transcript abundance increased by ~4-fold in the shoots of Pi -starved plants. 3 4 5 6 7 Days after transfer CONCLUSIONS AtGRP8 transcript abundance increased in both roots and shoots during Pi starvation. AtGRP8 may be involved in the signaling pathway that governs the plants adaptive responses to Pi stress conditions. REFERENCES Carpenter, C.D., Kreps, J.A. and Simon, A.E. 1994. Genes encoding Glycine-rich Arabidopsis thaliana proteins with RNA-binding Motifs are influenced by Cold treatment and an Endogenous Circadian Rhythm. Plant Physiol 104:1015-1025. Kwak, K.J., Kim Y.O. and Kang, H. 2005. Characterization of transgenic Arabidopsis plants overexpressing GR-RBP4 under high salinity, dehydration and cold stress. Journal of Experimental Botany. ACKNOWLEDGEMENTS UWA Scholarship International Research Fund UWA University International Stipend Australian Research Council UWA Graduate Research Student Travel Award The School of Plant Biology Travel Assistance