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Macadamia nuts contain abundant source of unsaturated fat acid (UFA), but the molecular mechanism of biosynthesis of UFA remains to be further analyzed. Stearoyl acyl-carrier- protein desaturase catalyses the insertion of a double bond into saturated fatty acid bound in saturated acyl chains bound to ACP in higher plant, which is the key enzyme in unsaturated fatty acid biological synthesis pathway. The Macadamia intergrifolia plant as research object, the full-length gDNA and cDNA of SAD gene encoding stearoyl acyl-carrier- protein desaturase were isolated from M. integrifolia using PCR technique. The structure, function and expression pattern of MiSAD were preliminarily studied. The gDNA of SAD was 6947 bp and contained 3 exons and 2 introns. The open reading frame was 1191 bp and encoded 396 amino acids which was highly consistent with the public MtSAD sequence, and SAD was a water soluble enzyme with a total predicted molecular mass of 45.22 kDa and isoelectric point (pI) 5.93 located in chloroplast or plasmids stroma. The amino acid sequences of SAD involved in active site showed highly conserved and significant difference in N-end and C-end. The highly conserved region contained 2 central motifs of E-X-X-H iron atoms which formed the active site of this enzyme. The α-helix and random curl were predominate in the secondary structure. The helix-turning-helix was found in the prediction of tertiary structure for formation of fatty acyl chain binding site. Derived amino acid sequence showed the highest homology 94.2% with Telopea speciosissima, and the homology is above 80%in other species of SAD, close to Nelumbo nucifera in phylogentic tree. The SAD gene expression trends were basically identical by qRT-PCR. The SAD expression were found in root, stem, leaf, flower and macadamia nut, and the highest level was in nut. The expression of SAD gene increased about 90days after and reached the highest level at 100 days, then declined gradually in the following days during the macadamia nut maturation and presenting a normal distribution trend. This study would build a foundation for elucidating the molecular mechanism of MiSAD in biosynthesis of unsaturated fatty acid in macadamia.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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