Epigenetics Mechanism Studies Of Maize Seedling Root Under Treatment Of Nitrogen Deficiency And Re-adding Nitrogen

Nitrogen is one of the most important elements for plant growth and development. The amount of nitrogen can affect produce and activity of enzymes related to photosynthesis, so the photosynthesis capability is affected. When nitrogen is deficit, many physiological and biochemical in plant would be affected. But, more nitrogen using also has bad effect on plant growth and development. So, how to using nitrogen and how to improve their efficiency have direct effect on food production in agriculture. Plant absorb nitrogen through root primarily, root anatomy and structure have an influence on nitrogen assimilate. NO3--N is the primary nitrogen in soil, it would be assimilated by nitrate reductase when absorbed from soil. So reductase activity is very important to NO3--N using. Amino acid is the basic unit of protein. The nitrogen amount can affect amount of amino acid, then affect synthesis of most protein involved in metabolism. Cytosine often has a chemical modification in plant genomic DNA sequence. That is the DNA cytosine methylation. Many studies have concluded that DNA methylation is related to stress response. MicroRNA is22nt length and single strand RNA. MicroRNA (miRNA) have been found in many eukaryotes and involved in many biological processes, such as cell proliferatioin, apoptosis, differentiation, development and stress response. In this study, we studied the change of root anatomy, nitrate reductase and amino acid, and root DNA methylation and miRNA under the treatment of nitrogen deficiency and nitrogen re-adding. Our purpose is to reveal the epigenetic mechanism of nitrogen deficiency, understand the mechanism and provide some theoretical basis for nitrogen using. The main results were showed below:1. The total root length, root surface area, split root number, the lateral root are larger under nitrogen deficiency than normal treatment. Under nitrogen deficiency treatment, when the primary root is shorter, the lateral root is longer and the one near primary root or root tip is longest, it can be20-30cm length; when the primary is longer, the lateral root near root tip is shorter and those closing primary is longer, they can be5-10cm.2. Root activity declined greatly under nitrogen deficiency treatment, the decline is 50.91%; when re-adding nitrogen, root activity can be recovered, but the activity is still declined greatly than normal treatment, the decline is42.15%.3. The proportion of root aerenchyma is small and inter tissue cell number is larger there are2-3endodermis; but under nitrogen deficiency, root aerenchyma developed early, endodermis decreased, and the2-3layer cell developed incompletely. The layer of endodermis is between nitrogen deficiency and normal treatment when re-adding nitrogen.4. Amount of root NO3-N decreased significantly, the decline is76.21%under nitrogen deficiency; the amount recovered in some extent when re-adding nitrogen, but still lower40.97than normal treatment.5. Root nitrate reductase increased a little, the increase is4.26%under nitrogen deficiency; when re-adding nitrogen, nitrate reductase is lower4.43%than normal treatment,8.33%than nitrogen deficiency treatment.6. Amount of Asp, Thr, Ser, Glu, Pro, Gly and Ala in root decreased under nitrogen deficiency treatment; when re-adding nitrogen, these seven amino acids amount are still lower than normal treatment, but amount of Cys, Met, Tyr and His are higher than normal treatment, and the amount of Cys, Tyr and His are lower than nitrogen deficiency treatment.7. The proportion of root genomic DNA methylation is19.92%under normal treatment, but the proportion increased a little under nitrogen deficiency or re-adding nitrogen treatment, the increase is22.46%and21.69%respectively.8. The proportion of20-24nt small RNA are all higher under three different treatment; the proportion of24nt and21nt small RNA are38.92%,19.60%;57.29%,14.44%,48.50%,16.87% under normal, nitrogen deficiency and re-adding nitrogen treatment respectively.The rRNA proportion are all lower under three different treatment, the proportion are6.05%,2.32% and3.44%; the proportion noncoding small RNA(including snoRNA) in all reads are0.19%,0.12% and0.19%; the proportion of miRNA is0.58%,0.40% and0.51%; the annotate proportion is63.11%,66.38% and64.70% respectively.9. The first base of20-23nt miRNA preference A and U under normal and nitrogen deficiency treatment; the first base of21nt and22nt miRNA preference A and U also under re-adding nitrogen treatment, but preference A and G for20nt and23nt miRNA; the first base preference C under all three different treatment.937new miRNA were predicted under three different nitrogen treatment. Among them,133were predicted under three nitrogen treatment;48were predicted under nitrogen deficiency and re-adding treatment;75were predicted under normal and re-adding nitrogen treatment;59were predicted under normal and nitrogen deficiency treatment;244were predicted under normal treatment,186were predicted under nitrogen deficiency treatment and 192were predicted under re-adding nitrogen treatment.10. Using MiPred, false-positive of937new predicted miRNA were screened. After adjust their p-value and combined their expression count,11miRNA related with nitrogen using were confirmed.The result of northern-blotting showed that miR1002, miR0944and miR0249had hybridization blot. And these miRNA are very impossible with maize nitrogen using.