| In this article, we analyzed the diversity and transmission of nod genes. We also induced, extracted and detected nod factor and used nod factor and its complex as fertilizer to improve the growth of soybeans.Rhizobia are a kind of bacteria involving in biological N-fixation. The symbiosis of rhizobia and leguminia fixes more than half of the total N-fixing quantity in the world. More and more rhizobia resources have been found and the traditional rhizobia taxonomy has gave way to phylogenetic analysis methods. To a certain extent, phylogenetic taxonomy is more reliable and reasonable than the traditional one. Nod factors are a general class of signal molecules produced by rhizobia, which play a key function in the initial steps of nodulation. The backbone structure of Nod factors is three to five 1,4-β-linked N-acetylglucosoamines and the non-reducing end is deacetylated and linked with an unsaturated fatty acid chain. There are many other substitutions on the lipo-chito-oligosacchride (LCO) backbone such as methyl or acyl on non-reducing end and sulphur or glycosyl on reducing end. Many researches have shown that different substitutions on the backbone play a key role in deciding the specificity between bacteria and the host plants. Different structures of nod factors are synthesized by products of so-called nod genes and the diversity of nod factors indicates the diversity of nod genes. Nod factors have many physiological effects on legumes. For example, they can induce soybean cortex cell-division, root hair curling, plasma membrane depolarization, actin fibril recombination, flow of plasma speedup and so on. In addition, nod factors can promote growth of plants and germination of seeds. Nod factors could act as a kind of molecular plant-growth-promoter applied in agriculture. In this article, we identified 4 Bradyrhizobium strains by 16S rRNA gene and analyzed diversity of nod genes of Bradyrhizobium. We determined possible way of nod genes transmission of Bradyrhizobium genus by phylogenetic analysis. We also induced nod factors of Bradyrhizobium strains. In the end nod factor was used as bio-fertilizer to improve soybean growth. The main results were displayed below:1. 16S rRNA genes of four rhizobia were sequenced and the sequences were blasted on the GenBank, the results showed that four strains were all belong to the Bradyrhizobium genus. The phylogenetic analysis based on 16S rRNA genes of Bradyrhizium genus was conducted and we made out that 4 rhizobia strains were belong to Bradyrhizobium genus.2. With the purpose to study the manner of nod genes transmit, we analyzed the phylogenetic trees of some symbiotic nodulation genes (containing nodA nodZ, nolL, and noeI) within the bradyrhizobium genus, comparing with that of the housekeeping genes such as 16S rRNA and dnaK genes. The result showed that the phylogenetic relationship of nod genes was mainly in accordance with each other, so as to housekeeping genes. So we presumed that the spread and maintenance of nodulation genes within the Bradyrhizobium genus occurred through vertical transmission and lateral gene transfer also played a significant role.3. We also conducted a series of experiment, e.g. Bradyrhizobium strains cultivating, nod factors inducement by genistein and legume root exudates, and nod factors detecting with HPLC (high performance liquid chromatogram) and biological essay-root hair deformation. The result showed that both genistein and legume root exudates were effective inducer of nod factors and different nod factors were induced by different inducers from the same Bradyrhizobium strain. Interestingly, the kind of nod factors induced by legume root exudates was much more than that by genistein.4. 10-8 M Nod factors were used as fertilizers in a field experiment and microelements boron and molybdenum were added as accelerant. The results showed that nod factors had positive effects on legumes such as the improvement of nodule number, plant-height, plant gross weight, biological quantity and production of soybean. But the microelements of boron and molybdenum didn't display obvious improvement.In the article, we studied the transmission of nod genes and the results could act as supplement of the evolutionary theory of rhizobia nod genes. On the other hand, we induced nod factors with genistein and extract of soybean roots. We also primarily researched the application of nod factor and its complex and we established the theoretical basis of the application of nod factor in agricatural production. |
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