A Comparative Proteomics Survey of Proteins Responsive to Phosphorous Starvation in Roots of Hydroponically-grown Rice Seedlings

Abstract

Rice takes up phosphorous (P) as major nutrient source for its growth and development when grown under anaerobic water-logged soil conditions. To better understand the underlying mechanisms and to develop potential protein biomarkers of P-starvation, hydroponically-grown rice seedlings in the complete media and phosphorus absence (P-starvation) of phosphorous nutrient solutions were investigated for physiological and proteome changes. The P-starvation manifested significant reduction in root growth in three-week-old seedlings compared to respective complete media. Furthermore, P-starvation also showed increased activity of acid phosphatase in roots of one- and three-week-old seedlings, suggesting that experimental design is suitable for proteomics survey of P-starvation responsive proteins. Two-dimensional gel electrophoresis coupled with matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry analysis of total root protein from three-week-old seedlings identified 10 P-starvation responsive protein spots out of 140 high-quality protein spots. Identified 10 proteins were involved in metabolism and defense/stress response. Out of 10, 2 and 8 protein spots were found to be up- and down-regulated, respectively. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis of corresponding genes of four randomly selected proteins, including putative glyceraldehydes-3-phophate dehydrogenase (G3PDH, spot R1), S-adenosyl-L-methionine synthetase (SAMS, spot R4), ATP synthase subunit alpha (spot R6), and root-specific pathogenesis-related protein 10 (PR-10, spot R8), showed that just as protein abundance, these proteins are also regulated at the transcript level. Results suggest identified P-starvation responsive proteins are involved in maintaining nutrient homeostasis and/or associated with changes in root physiology under the absence of P.