Luchetti Andrea, Cesari Michele, Carrara Giuliano, Cavicchi Sandro, Passamonti Marco, Scali Valerio, Mantovani Barbara
Dipartimento di Biologia Evoluzionistica Sperimentale, Via Selmi 3, Università di Bologna, Italia.
J Mol Evol. 2003 May;56(5):587-96. doi: 10.1007/s00239-002-2427-9.
Satellite DNA variability follows a pattern of concerted evolution through homogenization of new variants by genomic turnover mechanisms and variant fixation by chromosome redistribution into new combinations with the sexual process. Bacillus taxa share the same Bag320 satellite family and their reproduction ranges from strict bisexuality (B. grandii) to automictic (B. atticus) and apomictic (B. whitei = rossius/ grandii; B. lynceorum = rossius/grandii/atticus) unisexuality. Thelytokous reproduction clearly allows uncoupling of homogenization from fixation. Both trends and absolute values of satellite variability were analyzed in all Bacillus taxa but B. rossius, on 906 sequenced monomers at all level of comparisons: intraspecimen, intrapopulation, interpopulation, intersubspecies, and interspecies. For unisexuals, allozymic and mitochondrial clones were also taken into account. Different reproductive modes (sexual/parthenogenetic) appear to explain observed variability trends, supporting Dover's hypothesis of sexuality acting as a driving force in the fixation of sequence variants, but the present analyses also highlight current spreading of new variants in B. grandii maretimi specimens and point to a biased sequence inheritance at the time of hybrid onset in the apomictic hybrids B. whitei and B. lynceorum. Evidence of biased gene conversion events suggests that, given enough time, sequence homogenization can take place in a unisexual such as B. lynceorum. On the contrary, the absolute values of sequence diversity in each taxon are linked to the species' range, time of divergence, and repeat copy number and, possibly, to transposon features. Satellite dynamics appears therefore to be the outcome of both general molecular processes and specific organismal traits.
卫星DNA的变异性遵循一种协同进化模式，通过基因组周转机制使新变异同质化，并通过染色体重新分布将变异固定到与有性过程的新组合中。芽孢杆菌类群共享相同的Bag320卫星家族，其繁殖方式从严格的两性生殖（大芽孢杆菌）到孤雌生殖（阿提卡芽孢杆菌）和无融合生殖（怀特芽孢杆菌 = 罗西芽孢杆菌/大芽孢杆菌；林氏芽孢杆菌 = 罗西芽孢杆菌/大芽孢杆菌/阿提卡芽孢杆菌）的单性生殖。产雌孤雌生殖显然允许同质化与固定脱钩。在所有芽孢杆菌类群（除罗西芽孢杆菌外）中，对906个测序单体在所有比较水平（种内、种群内、种群间、亚种间和种间）的卫星变异性趋势和绝对值进行了分析。对于单性生殖的物种，还考虑了等位酶和线粒体克隆。不同的生殖模式（有性/孤雌生殖）似乎可以解释观察到的变异性趋势，这支持了多佛的假设，即有性生殖是序列变异固定的驱动力，但目前的分析也突出了大芽孢杆菌马雷蒂米标本中新变异的当前传播情况，并指出在无融合生殖杂种怀特芽孢杆菌和林氏芽孢杆菌杂交开始时存在偏向性的序列遗传。偏向性基因转换事件的证据表明，假以时日，序列同质化可以在像林氏芽孢杆菌这样的单性生殖物种中发生。相反，每个类群中序列多样性的绝对值与物种的分布范围、分化时间、重复拷贝数以及可能与转座子特征有关。因此，卫星动态似乎是一般分子过程和特定生物体特征共同作用的结果。
