Ochs G, Schock G, Trischler M, Kosemund K, Wild A
Institut für Allgemeine Botanik, Johannes Gutenberg-Universität Mainz, Germany.
Plant Mol Biol. 1999 Feb;39(3):395-405. doi: 10.1023/a:1006193717093.
In the amphidiploid genome of oilseed rape (Brassica napus) the diploid ancestral genomes of B. campestris and B. oleracea have been merged. As a result of this crossing event, all gene loci, gene families, or multigene families of the A and C genome types encoding a certain protein are now combined in one plant genome. In the case of the multigene family for glutamine synthetase, the key enzyme of nitrogen assimilation, six different cDNA sequences were isolated from leaf and root specific libraries. One sequence pair (BnGSL1/BnGSL2) was characterized by the presence of amino-terminal transit peptides, a typical feature of all nuclear encoded chloroplast proteins. Two other cDNA pairs (BnGSR1-1/BnGSR1-2 and BnGSR2-1/BnGSR2-2) with very high homology between each other were found in a root specific cDNA library and represent protein subunits for cytosolic glutamine synthetase isoforms. Comparative PCR amplifications of genomic DNA isolated from B. napus, B. campestris and B. oleracea followed by sequence-specific restriction analyses of the PCR products permitted the assignment of the cDNA sequences to either the A genome type (BnGSL1/BnGSR1-1/BnGSR2-1) or the C genome type (BnGSL2/BnGSR1-2/BnGSR2-2). Consequently, the ancestral GS genes of B. campestris and B. oleracea are expressed simultaneously in oilseed rape. This result was also confirmed by RFLP (restriction fragment length polymorphism) analysis of RT-PCR products. In addition, the different GS genes showed tissue specific expression patterns which are correlated with the state of development of the plant material. Especially for the GS genes encoding the cytosolic GS isoform BnGSR2, a marked increase of expression could be observed after the onset of leaf senescence.
在油菜（甘蓝型油菜）的双二倍体基因组中，白菜型油菜和甘蓝的二倍体祖先基因组已经融合。由于这次杂交事件，编码某种蛋白质的A和C基因组类型的所有基因座、基因家族或多基因家族现在都组合在一个植物基因组中。就氮同化的关键酶谷氨酰胺合成酶的多基因家族而言，从叶片和根特异性文库中分离出了六个不同的cDNA序列。一对序列（BnGSL1/BnGSL2）的特征是存在氨基末端转运肽，这是所有核编码叶绿体蛋白的典型特征。在根特异性cDNA文库中发现了另外两对彼此具有非常高同源性的cDNA（BnGSR1-1/BnGSR1-2和BnGSR2-1/BnGSR2-2），它们代表胞质谷氨酰胺合成酶同工型的蛋白质亚基。对从甘蓝型油菜、白菜型油菜和甘蓝中分离的基因组DNA进行比较PCR扩增，然后对PCR产物进行序列特异性限制性分析，从而将cDNA序列指定为A基因组类型（BnGSL1/BnGSR1-1/BnGSR2-1）或C基因组类型（BnGSL2/BnGSR1-2/BnGSR2-2）。因此，白菜型油菜和甘蓝的祖先GS基因在油菜中同时表达。RT-PCR产物的RFLP（限制性片段长度多态性）分析也证实了这一结果。此外，不同的GS基因表现出与植物材料发育状态相关的组织特异性表达模式。特别是对于编码胞质GS同工型BnGSR2的GS基因，在叶片衰老开始后可以观察到表达明显增加。
