Natali L, Santini S, Giordani T, Minelli S, Maestrini P, Cionini P G, Cavallini A
Dipartimento de Biologia della Piante Agrarie, Sezione de Genetica, Pisa, Italy.
Genome. 2006 Jan;49(1):64-72. doi: 10.1139/g05-058.
Two repeated DNA sequences, pHaS13 and pHaS211, which revealed similarity to the int gene of Ty3-gypsy retrotransposons and the RNAse-H gene of Ty1-copia retroelements, respectively, were surveyed in Asteraceae species and within the genus Helianthus. Southern analysis of the genome of selected Asteraceae that belong to different tribes showed that pHaS13- and pHaS211-related subfamilies of gypsy- and copia-like retroelements are highly redundant only in Helianthus and, to a lesser extent, in Tithonia, a Helianthus strict relative. However, under low stringency posthybridization washes, bands were observed in almost all the other Asteraceae tested when pHaS13 was used as a probe, and in several species when pHaS211 was hybridized. FISH analysis of pHaS13 or pHaS211 probes was performed in species in which labelling was observed in Southern hybridizations carried out under high stringency conditions (Helianthus annuus, Tithonia rotundifolia, Ageratum spp., Leontopodium spp., Senecio vulgaris for pHaS13, and H. annuus, Tithonia rotundifolia, and S. vulgaris for pHaS211). Scattered labelling was observed over all metaphase chromosomes, indicating a large dispersal of both Ty3-gypsy- and Ty1-copia-like retroelements. However, preferential localization of Ty3-gypsy-like sequences at centromeric chromosome regions was observed in all of the species studies but one, even in species in which pHaS13-related elements are poorly represented. Ty1-copia-like sequences showed preferential localization at the chromosome ends only in H. annuus. To study the evolution of gypsy- and copia-like retrotransposons in Helianthus, cladograms were built based on the Southern blot hybridization patterns of pHaS13 or pHaS211 sequences to DNA digests of several species of this genus. Both cladograms agree in splitting the genomes studied into annuals and perennials. Differences that occurred within the clades of perennial and annual species between gypsy- and copia-like retroelements indicated that these retrotransposons were differentially active during Helianthus speciation, suggesting that the evolution of the 2 retroelement families was, within limits, independent.
在菊科植物和向日葵属中对两个重复DNA序列pHas13和pHas211进行了研究，它们分别与Ty3-gypsy逆转录转座子的int基因和Ty1-copia逆转录元件的RNA酶H基因具有相似性。对属于不同族的选定菊科植物基因组进行的Southern分析表明，与pHas13和pHas211相关的类gypsy和类copia逆转录元件亚家族仅在向日葵中高度冗余，在向日葵的近缘种肿柄菊中冗余程度较低。然而，在低严谨度的杂交后洗涤条件下，当使用pHas13作为探针时，在几乎所有其他测试的菊科植物中都观察到条带，当pHas211杂交时，在几个物种中观察到条带。在严格条件下进行Southern杂交时观察到标记的物种（对于pHas13为向日葵、肿柄菊、藿香蓟属、雪兔子属、普通千里光，对于pHas211为向日葵、肿柄菊和普通千里光）中，对pHas13或pHas211探针进行了荧光原位杂交（FISH）分析。在所有中期染色体上均观察到分散的标记，表明类Ty3-gypsy和类Ty1-copia逆转录元件均有大量分散。然而，在所研究的所有物种（除一个物种外）中均观察到类Ty3-gypsy序列在着丝粒染色体区域的优先定位，即使在pHas13相关元件含量较低的物种中也是如此。类Ty1-copia序列仅在向日葵中显示出在染色体末端的优先定位。为了研究向日葵中类gypsy和类copia逆转录转座子的进化，根据pHas13或pHas211序列与该属几个物种的DNA酶切产物的Southern杂交模式构建了系统发育树。两个系统发育树都一致地将所研究的基因组分为一年生植物和多年生植物。多年生和一年生物种的类gypsy和类copia逆转录元件在进化枝内出现的差异表明，这些逆转录转座子在向日葵物种形成过程中具有不同的活性，这表明这两个逆转录元件家族的进化在一定程度上是独立的。
