Transcription Levels Of The Genes Encoding NO₃^-Transporter Families And Protromic Analysis Of Wheat Seedling Roots In Response To Nitrogen Starvation

Nitrogen (N) is the major macronutrients required for plant growth anddevelopment，and also the constituent of key cell molecules such as amino acids,nucleic acids, chlorophyll, ATP and several plant hormones. However, there is Ndeficiency in most of cultivated soils in the world. To enable plants to use N moreefficiently, therefore, it is essential to understand the molecular basis of plantresponses to N deficiency.In the present study, we analysis the transcription of the genes encoding NO–3transporter NRT1and NRT2families and the proteomic mechanisms of the wheatseedling root response to nitrogen starvation. The main results of this study are asfollows:(1) Nitrogen (N) starvation for8days significantly inhibited the growth of wheatseedlings, manifested by decreased plant heights, shoot fresh weights, shoot dryweights, although it stimulated the root growth. During N starvation, contents ofchlorophyll, carotenoid, nitrates and protein were remarkably reduced, whereascontents of malondialdehyde (MDA) were markedly increased in leaves and roots ofwheat seedlings during N starvation.(2) Seven (TaNRT1.1, TaNRT1.2, TaNRT1.3, TaNRT1.4, TaNRT1.5, TaNRT1.7, andTaNRT1.8) and five (TaNRT2.1, TaNRT2.2, TaNRT2.3, TaNRT2.4, and TaNRT2.5)putative cDNA sequences of genes associated with NRT1and NRT2were found inbread wheat.(3) Twelve genes encoding the NRT1and NRT2families in common wheat wereidentified and their transcription levels were further measured using quantitativereal-time PCR (qPCR) in roots of N starved wheat seedlings. The results indicatedthat N starvation significantly enhanced the transcription levels of TaNRT1.1at2and4days; TaNRT1.3at2,4, and6days; TaNRT1.4at2days; TaNRT1.7and TaNRT1.8at2days; TaNRT2.1and TaNRT2.2at2days; and TaNRT2.3at2and4days. However,the TaNRT1.5and TaNRT2.4genes were greatly inhibited at all sampling time pointsafter N starvation, whereas the TaNRT1.2and TaNRT2.5genes were induced dramatically.(4) To investigate the molecular mechanism of wheat seedling responses to Nstarvation, we obtained root proteome profiles using isobaric tags for relative andabsolute quantitation (iTRAQ) after8days of N starvation. Of3681spots detected,134were differentially expressed (ratio>1.5or ratio<0.67, and P≤0.05). These134spots wereanalyzed by LC-MS/MS, and the protein identities of66spots weredetermined. Analysis of protein expression patterns in roots revealed that the66proteins associated with signal transduction, nitrogen metabolism, carbohydratemetabolism, stress defense, transpoter and energy production. Of16proteins involvedin nitrogen metabolism,5proteins were up-regulated,11proteins weredown-regulated; of11proteins involved in carbohydrate metabolism,5proteins wereup-regulated,6proteins were down-regulated; of30proteins involved in stressdefense,10proteins were up-regulated,20proteins were down-regulated; of5proteins involved in transpoter,1proteins were up-regulated,4proteins weredown-regulated; of3proteins involved in carbohydrate metabolism,1proteins wereup-regulated,2proteins were down-regulated. These proteins may play importantroles in wheat seedlings in response to N starvation.