Leach C R, Donald T M, Franks T K, Spiniello S S, Hanrahan C F, Timmis J N
Department of Genetics, The University of Adelaide, Adelaide, South Australia 5005, Australia.
Chromosoma. 1995 Jul;103(10):708-14. doi: 10.1007/BF00344232.
Brachycome dichromosomatica is an Australian native daisy that has two pairs of A chromosomes and up to three B chromosomes in some populations. A putative B-specific tandem repeat DNA sequence (Bd49) was isolated previously. Here we describe further characterisation of this sequence and investigate its possible origin. Southern analysis showed that all individual B chromosomes examined have highly methylated tandem repeats of Bd49 but differences in banding pattern for distinct B isolates suggested that the sequence is in a state of flux. Using in situ hybridisation, the sequence was shown to be located at the centromeric region of the B chromosome. Southern analysis of genomic DNA with Bd49 demonstrated that multiple copies of the sequence exist in the genomes of B. eriogona, B. ciliaris, B. segmentosa and B. multifida (none of which have B chromosomes) whereas other species tested (including 0B plants of B. dichromosomatica and 0B and +B B. curvicarpa and B. dentata) have few or no copies. Genomic clones and Bd49-like sequences derived by the polymerase chain reaction (PCR) were obtained from five species but determination of phylogenetic relationships within the genus and inference as to the possible origin of the B chromosome were problematic because of extensive intragenomic heterogeneity of the sequences.
二色短舌菊是一种澳大利亚本土雏菊，在一些种群中有两对A染色体和多达三条B染色体。先前已分离出一种假定的B特异性串联重复DNA序列（Bd49）。在此，我们描述了该序列的进一步特征，并研究了其可能的起源。Southern分析表明，所有检测的单个B染色体都有高度甲基化的Bd49串联重复序列，但不同B分离株的条带模式差异表明该序列处于变化状态。通过原位杂交，该序列显示位于B染色体的着丝粒区域。用Bd49对基因组DNA进行Southern分析表明，该序列的多个拷贝存在于糙短舌菊、睫毛短舌菊、节状短舌菊和多裂短舌菊（均无B染色体）的基因组中，而其他测试物种（包括二色短舌菊的0B植株以及0B和+B的弯果短舌菊和齿叶短舌菊）则只有很少拷贝或没有拷贝。通过聚合酶链反应（PCR）从五个物种中获得了基因组克隆和Bd49样序列，但由于序列在基因组内存在广泛的异质性，确定该属内的系统发育关系以及推断B染色体的可能起源存在问题。
