| Different pigments make the plants appears various colours in different plant species or in different stage of one species. Normally, green plant's leaf is green since they are containing abundant chlorophyll (chl). The composition of pigments in leaves is under the influence of genetic and environmental stimuli, and is the result of the balance between synthesis and degradation of pigments. In recent years, the anabolic chl pathway has been studied clearly. For the chl catabolism, researchers have a new understanding about the initial period of chlorophyll degradation through the study of stay-green mutant sgr(t) in Oryza sativa. At present, the identification of SGR gene has been detected in many other species. Loss the function of SGR gene can cause a phenotype of"stay-green"in green plant,but the mechanism of the stay-green mutation is still unknown at present. The study of different SGR gene and stay-green mutant sgr(t) from various species can be useful to prove up its mechanism and the pathway of chlorophyll degradation.In this study, through homology analysis of the existing SGR gene, we designed specific primers, and have cloned the code area of SGR gene of the cabbage and potherb mustard. We carried out the bioinformatics analysis of the sequence, and studied the expression pattern of SGR gene of potherb mustard. To further study the function of potherb mustard and cabbage SGR gene, We have constructed SGR gene silencing RNAi vector of potherb mustard and cabbage, and have carried out genetic transformation of Brassica juncea with floral-dip and tissue culture transformation by Agrobacterium-mediated. The main results of the study as follows:①The code area of SGR gene of the cabbage and potherb mustard have been cloned successfully. The results of sequencing show that the sequence of them are 807bp, and they are almost completely homology, only three base differences. The homology of potherb mustard with Arabidopis thaliana(NYE1) is 85%,Wuta-tsai91%,tobacco77%,tomato76% and so on.②Through bioinformatics analysis, it manifest that the SGR gene of the cabbage and potherb mustard both encode 268 amino acid residues, and the sequence is same, the molecular mass of it is 30.3 kDa and isoelectric point is 8.56,and the protein encoded by BjSGR gene is a non-secreted protein, and has a N terminal chloroplast transit peptide and signal peptide. It supposed that it may directly participate in the signal transduction or response since it doesn't have a transmembrane domain, and have many multiple phosphorylation sites. The amino acid sequence of which encode have a highly homology with other SGR proteins, and have a highly conserved C-terminal motif(C-X3-C-X-C2-F-P-X5-P),and the homology with Arabidopis thaliana(NYE1) is 87%, rice 61%. The homology with the SGR protein of Wuta-tsai of Brassica is 92%, except for more 21 amino acids, only one amino acid is different. By comparing the amino acid sequence with other species, except for Zoysia(the whole amino acid sequence is short),there is not the more 21 amino acids sequence in other species. This further illustrates that the sequence may be inserted in a later stage, and that may be lead to loss of function of Wuta-tsai SGR gene.③Through the expression analysis of SGR gene in potherb mustard(Brassica juncea var. crispifolia , BjSGR),it showed that BjSGR is induced by senescence and lead to specific expression. In young leaves, its expression level is low, but the expression level increase rapidly in senescent leaves that green slightly come out.④Through the exploration and improvement of floral-dip of Arabidopis thaliana, transgenic potherb mustard(potherb potherb mustard, Brassica juncea var. crispifolia) was obtained via performing direct drop-by-drop inoculation to every bud by using a pipette. Meanwhile, with the study on the factors which may affect the transformation efficiency, such as sucrose concentration, surfactant concentration, and the OD600 of the Agrobacterium inoculum, it showed that a higher transformation efficiency can be gotten by using 5% sucrose (w/v)+0.03%Silwet-77(v/v) resuspended Agrobacterium when the OD600 of the Agrobacterium inoculum was 0.8, and the transformation rate was 2.3%. The method avoids vacuum processing and influence of immerged time, which makes the manipulation simpler and the transformation period shorter, thus a more convenient method of transformation for the genetic transformation of potherb mustard was provided.⑤In the tissue culture transformation experiment, kinds of explants and hormone combination have been done. The results showed that the regeneration rate of bud of cotyledon is rather high in 2 mg/ L 6-BA + 0. 2 mg/ L NAA group, the resistance of seedlings was obtained, which is in the rooting stage at present. This laid a good foundation for the study of function of potherb mustard and cabbage SGR gene.
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