Barros E Silva A E, Dos Santos Soares Filho W, Guerra M
Department of Biology, Federal University of Paraíba, Areia, Brazil.
Cytogenet Genome Res. 2013;140(1):62-9. doi: 10.1159/000350695. Epub 2013 Apr 27.
Sites of 5S and 45S rDNA are more commonly located on different chromosomes of most angiosperms. Previous investigations have shown that in the subfamily Aurantioideae these sites may appear closely linked (adjacent sites), as in Poncirustrifoliata, or completely isolated, as in some species of Citrus. In the present work, the distribution of rDNA sites was investigated in representatives of 9 genera of Aurantioideae by FISH and CMA banding, aiming to understand the evolution of adjacent sites in the subfamily. A total of 57 rDNA sites were observed, 40 of them being adjacent to each other. All adjacent sites displayed the 45S rDNA array more terminally located. Assuming that the linked 5S-45S rDNA arrangement was the ancestral condition in Aurantioideae, the isolated rDNA sites observed in Clausena excavata,Bergera koenigii, and Fortunella obovata, as well as the complete linkage loss in Citrus maxima and C. medica indicates that unlinked sites arose independently several times in the evolution of the group. The linkage loss may be due to independent dispersion of one or both rDNA sequence families followed by deletion of the corresponding array in the adjacent site. The possible mechanisms behind these events and their occurrence in other groups are discussed.
5S和45S核糖体DNA（rDNA）位点在大多数被子植物的不同染色体上更为常见。先前的研究表明，在柑橘亚科中，这些位点可能紧密相连（相邻位点），如枳，或者完全分离，如某些柑橘属物种。在本研究中，通过荧光原位杂交（FISH）和染色体带型分析（CMA带型）研究了柑橘亚科9个属代表植物的rDNA位点分布，旨在了解该亚科中相邻位点的进化情况。共观察到57个rDNA位点，其中40个彼此相邻。所有相邻位点的45S rDNA阵列都更靠近末端。假设连锁的5S - 45S rDNA排列是柑橘亚科的原始状态，那么在山油柑、臭常山和金橘中观察到的孤立rDNA位点，以及在柚和酸橙中完全丧失的连锁关系表明，在该类群的进化过程中，不连锁的位点独立出现了几次。连锁关系的丧失可能是由于一个或两个rDNA序列家族的独立分散，随后相邻位点的相应阵列缺失。本文讨论了这些事件背后的可能机制及其在其他类群中的发生情况。
