Molecular and cytogenetic studies to estimate genome size reduction of chromosomal DNA in genus Aster

裙带菜的核型在形态上与阿斯特的核型相似，但裙带菜的染色体长度（s型染色体）明显小于阿斯特（l型染色体）。先前的细胞遗传学和叶绿体DNA数据表明，小头A. var. ovatus （ls型染色体）的杂交起源。叶绿体DNA系统发育也表明S型染色体是无胚性的。这意味着在山裙菜的进化过程中发生了基因组大小的减少。在这项研究中，我们证明了染色体大小的差异不取决于染色体凝聚的强度，而取决于DNA的含量。同时，GISH结果显示，pirmatifida和a . microcephalus var. ovatus的s型染色体具有相似性，ageratoides和a . microcephalus var. ovatus的l型染色体具有相似性，这进一步证明了a . microcephalus var ovatus是由s型染色体和l型染色体产生的四倍体雌雄二倍体。在l型和s型染色体中，类tyl拷贝型反转录转座子的分布模式相似。该反转录转座子的拷贝均匀地分布在所有染色体上，而Tyl-copia样反转录转座子是否与它们之间的大小差异不明显。

The karyotype of Kalimeris pinnatifida is morphologically similar to those of Aster ageratoides var. ageratoides, however, the size of the chromosomes of K pinnatifida is apparently smaller (S-type chromosomes) compared to those of A. ageratoides (L-type chromosomes). And the hybrid origin of A. microcephalus var. ovatus (LS-type chromosomes) is previously suggested by cytogenetics and chloroplast DNA data. The chloroplast DNA phylogeny also implies that the S type chromosome is apomorphic. It means genome size reduction happened on the evolutionary way to K. pinnatifida. In this study we demonstrated that the chromosome size difference do not depend on the intensity of chromosome condensation but the DNA contents. And the simultaneous GISH results here showed the similarity between S-type chromosomes of K pirmatifida and A. microcephalus var. ovatus, and between L-type chromosomes of A. ageratoides and A. microcephalus var. ovatus, which provided additional evidence for A. microcephalus var. ovatus being a tetraploid amphidiploid produced by the S-type chromosomes and the L-type chromosomes. The distribution patterns of Tyl-copia like retrotransposons were similar between L-and S-type chromosomes. The copies of this retrotransposon dispersed uniformly on all chromosomes, and it is not apparent if the Tyl-copia like retrotransposon concerned the size difference between them.