Identification Of Nitrate-induced Genes By Suppression Subtractive Hybridization (SSH) And Their Expression Pattern Analysis In Rice Root

Lateral root (LR) is primary organ for plant to explore and utilize soil nutrient. To investigate the effect of nitrate (NO3-) on rice lateral roots growth and nitrogen (N) uptake efficiency under upland condition, three treatments, including split-root culture and whole plant culture in N sufficient and deficient conditions, were used in a vermiculite culture experiments. Split-root treatment (rice was grown with half roots supplied with 3 mmol/L NO3- and another half with 3 mmol/L KCL) showed that the growth of lateral roots was stimulated by localized nitrate supply. However, in whole plant culture, elongation of lateral roots was induced by NO3- deficiency. The effects of NO3- on rice lateral roots growth were genotype-dependent among five genotypes. Similar N concentrations soluble sugar concentration and N content in shoot were observed in both split-root treatment and whole plant culture under NO3- sufficient condition, which suggests that the N requirement for rice normal growth could be satisfied with only half of roots supplied with NO3-. In the split-root treatment, N uptake was positively correlated with the average of lateral root length (ALRL) in NOs3--supplied side, suggesting that the ALRL is important for rice root N uptake in the environment where the N nutrient is limiting factor. However, no significant correlation was observed between N uptake and ALRL in whole plant culture under N sufficient condition, which implies that the lateral roots length may not be the main factor to determine the rice root N uptake in nutrient-rich zone.Nitrate could stimulate the rice lateral root growth and make most of roots proliferation in the nutrient-rich zone, thus improve rice N uptake efficiency. To identify nitrate-induced genes in rice roots, a nitrate-induced root subtracted library was constructed using the suppression subtractive hybridization (SSH) method in split-root experiment system. Based on forward and reverse screening, 39 known genes and 55 novel genes were identified to be up-regulated in nitrate-supplied side roots. These known genes are involved in N uptake and assimilation, sugar transport and organic acid metabolism, signal transduction, protein synthesis and degradation, plant resistance, hormone metabolism and cell division. Most of these genes werestronger up-regulated in nitrate-supplied side roots than in nitrate-deficient side roots, suggesting that nitrate may regulate the genes expressions. Expression pattern analysis revealed that a quick cycle of assimilated N metabolites occurred between root and shoot. Transcription of some nitrate induced genes were also up-regulated in nitrate-deficient side roots, implied that nitrate coordinately with N metabolites from shoot, regulate the transcription of many genes in rice. The enhancement of carbon (C) source partition, the expressions of genes for signal transduction and transcription regulation, auxin transport and ethylene synthesis, and CDKs may be responsible for the stimulated lateral root growth by nitrate.