Short interspersed nuclear elements (SINEs) are small non-autonomous and heterogeneous retrotransposons, widespread in animals and plants and usually differentially propagated in related species resulting in genome-specific copy numbers.
Within the monocots, the Poaceae (sweet grasses) is the largest and economically most important plant family. The distribution of 24 Poaceae SINE (PoaS) families, five of which showing a subfamily structure, was analyzed in five important cereals (Oryza sativa, Triticum aestivum, Hordeum vulgare, Sorghum bicolor, Zea mays), the energy crop Panicum virgatum and the model grass Brachypodium distachyon. The comparative investigation of SINE abundance and sequence diversity within Poaceae species provides insights into their species‐specific diversification and amplification. The PoaS families and subfamilies fall into two length and structural categories: simple SINEs of up to 180 bp and dimeric SINEs larger than 240 bp. Of 24 PoaS families, 20 are structurally related across species, in particular either in their 5′ or 3′ regions. Hence, reshuffling between SINEs, likely caused by nested insertions of full-lengh and truncated copies, is an important evolutionary mechanism of SINE formation. Most striking, the recently evolved homodimeric SINE family PoaS‐XIV occurs exclusively in wheat (T. aestivum) and consists of two tandemly arranged PoaS‐X.1 copies.
Exemplary for deciduous tree species, the evolutionary history of SINE populations was examined in six Salicaceae genomes (Populus deltoides, Populus euphratica, Populus tremula, Populus tremuloides, Populus trichocarpa, Salix purpurea). Four of eleven Salicaceae SINE (SaliS) families exhibit a subfamily organization. The SaliS families consist of two groups, differing in their phylogenetic distribution pattern, sequence similarity and 3’ end structure. These groups probably emerged at different evolutionary periods of time: during the ‘salicoid duplication’ (~ 65 million years ago) in the Salix-Populus progenitor, and during the separation of the genus Salix (~ 45 - 65 million years ago), respectively. Similar to the PoaS families, the majority of the 20 SaliS families and subfamilies share regions of sequence similarity, providing evidence for SINE emergence by reshuffling. Furthermore, they also contain an evolutionarily young dimeric SINE family (SaliS-V), amplified only in two poplar genomes. The special feature of the Salicaceae SINEs is the contrast of the conservation of 5’ start motifs across species and SINE families compared to the high variability of
3’ ends within the SINE families, differing in sequence and length, presumably resulting from mutations in the poly(A) tail as a possible route for SINE elongation. Periods of increased transpositional activity promote the dissemination of novel 3’ ends. Thereby, evolutionarily older motifs are displaced leading to various 3’ end subpopulations within the SaliS families. Opposed to the PoaS families with a largely equal ratio of poly(A) to poly(T) tail SINEs, the SaliS families are exclusively terminated by adenine stretches.
Among retrotransposon-based markers, SINEs are highly suitable for the development of molecular markers due to their unidirectional insertion and random distribution mainly in euchromatic genome regions, together with an easy and fast detection of the heterogeneous SINE families. As a prerequisite for the development of SINE-derived inter-SINE amplified polymorphism (ISAP) markers, 13 novel Theaceae SINE families (TheaS-I - TheaS-VII, TheaS-VIII.1 and TheaS-VIII.2, TheaS-IX - TheaS-XIII) were identified in the angiosperm tree species Camellia japonica. Moreover, six Pinaceae SINE families (PinS-I.1 and PinS-I.2, PinS-II – PinS-VI) were detected in the gymnosperm species Larix decidua. Compared to the SaliS and PoaS families, structural relationships are less frequent within the TheaS families and absent in the PinS families.
The ISAP analysis revealed the genetic identity of Europe’s oldest historical camellia (C. japonica) trees indicating their vegetative propagation from the same ancestor specimen, which was probably the first living camellia on European ground introduced to England within the 18th century. Historical sources locate the native origin of this ancestral camellia specimen either in the Chinese province Yunnan or at the Japanese Gotō Islands. Comparative ISAPs showed no accordance to the Gotō camellia sample pool and appropriate Chinese reference samples were not available. However, the initial experiments demonstrated the potential of ISAP to resolve variations among natural populations.
The ISAP application on angiosperm trees also concerned fast growing Populus clones grown in short rotation coppice plantations for energy production. The species-specific P. tremula ISAP primers might also be applied for the discrimination of hybrid poplar clones involving P. tremuloides genome
portions, since SINEs of these two species are highly related. However, due to lineage-specific SINE evolution during speciation, cross-species applications are generally only successful to limited extent. The analysis of poplar hybrids composed of P. maximowiczii with either P. trichocarpa or P. nigra based on P. tremula ISAP primers showed a strongly reduced resolution.
In forestry, hybrid larch (e.g. Larix × eurolepis) genotypes have to be selected from the offspring of Japanese (Larix kaempferi) and European larch (Larix decidua) crosses, as they exhibit superior growth rates compared to the parental species. Initial ISAP-based examinations of European larch genotypes provided less polymorphic banding patterns, probably resulting from general high levels of synteny and collinearities reported for gymnosperm species. Hence, the ISAP was combined with the AFLP technique to the novel marker system inter-SINE-restriction site amplified polymorphism (ISRAP). The amplicons originating from genomic regions between SINEs and EcoRI cleavage sites were visualized with the sensitive capillary gel electrophoresis. The ISRAP assays, based on EcoRI adapter primers combined with two different SINE-derived primers, resulted in a sufficient number of polymorphic peaks to distinguish the L. decidua genotypes investigated. Compared to ISAPs, the ISRAP approach provides the required resolution to differentiate highly similar larch genotypes.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:72118 |
| Date | 08 September 2020 |
| Creators | Kögler, Anja |
| Contributors | Wanke, Stefan, Göttfert, Michael, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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