Phosphorus (P) is one of the most essential macronutrients required for plant growth. Although it is abundant in soil, P is often the limiting nutrient for crop yield potential because of the low concentration of soluble P that plants can absorb directly. The gene expression profile was investigated in rice roots at 6, 24 and 72 h under low P stress and compared with a control (normal P) profile, using a DNA chip of 60000 oligos (70 mer) that represented all putative genes of the rice genome. A total of 795 differentially expressed genes were identified in response to phosphate (Pi) starvation in at least one of the treatments. Based on the analysis, we found that: (i) The genes coding for the Pi transporter, acid phosphatase and RNase were up-regulated in rice roots; (ii) the genes involved in glycolysis were first up-regulated and then down-regulated; (iii) several genes involved in N metabolism and lipid metabolism changed their expression patterns; (iv) some genes involved in cell senescence and DNA or protein degradation were up-regulated; and (v) some transmembrane transporter genes were up-regulated. The results may provide useful information in the molecular process associated with Pi deficiency and thus facilitate research in improving Pi utilization in crop species.
LI LiHua, QIU XuHua, LI XiangHua, WANG ShiPing & LIAN XingMing National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China
A full-length cDNA that encodes the rice chloroplastic glutamine synthetase 2 gene was isolated from a Minghui 63-normalized cDNA library; and GS2 rice transformants were obtained by an Agrobacterium tumefaciens-mediated transformation method. Transcripts of the GS2 gene were shown to accumulate at higher levels in the primary transgenic plants in the T0 generation; whereas plants in the T1 generation exhibited a co-suppressed chlorosis phenotype (yellow leaves) accompanied by decreased plant height, few tillers and decreased dry weight. The plants with yellow leaves also displayed a significant decline in GS2 messenger RNA (mRNA) transcriptional level and chlorophyll content; a decrease in total GS activities of ~50% was also found. Although there was no decrease in the concentration of total free amino acids, a change in the concentration of individual amino acids was observed. Our result also indicates a decreased metabolic level (soluble protein content and ammonium concentration) in GS2 co-suppressed plants. A correlation between chlorophyll content and GS2 mRNA expression level was also observed. The GS2 co-suppressed plants showed better performance when complemented with exogenous glutamine, indicating that the lack of an organic nitrogen pool inside the cell is the possible reason for the chlorosis phenotype of the transformants.
Phosphorus is one of the essential macronutrients required for plant growth and development. The plants increase the absorption of phosphorus through an expansion of the root system in the soil when they are in low-phosphorus conditions. At the same time, the changes in biochemical metabolic pathways and the increase of secretion of phosphatase and organic acids activate the insoluble phosphate fixed in the soil. The expression profile in response to low phosphorus was investigated for rice at 6, 24 and 72 h after low-phosphorus stress compared with normal phosphorus conditions as a control with DNA chip. A total of 1207 differen- tially expressed genes were found in our study; 795 and 450 genes exhibited alterations in their RNA expression in response to inorganic phosphate (Pi) starvation in at least one of the three time points in roots and shoots. Thirty-eight genes overlapped in shoots and roots. The functional classification of these genes indicated their involvement in various metabolic pathways, ion transport, signal transduction, transcriptional regulation, and other processes related to growth and development. A large number of transposable elements changed the expression in rice after low-phosphorus stress. The results may provide useful information about molecular processes associated with Pi deficiency and facilitate the identification of key molecular determinants for improving Pi use by crop species.
LI LiHua QIU XuHua LI XiangHua WANG ShiPing ZHANG QiFa LIAN XingMing
