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BackgroundIt is widely accepted that interspecific hybridization may induce genomic instability in the resultant hybrids. However, few studies have been performed on the genomic analysis of homoploid hybrids and introgression lines. We have reported previously that by introgressive hybridization, a set of introgression lines between rice (Oryza sativa L.) and wild rice (Zizania latifolia Griseb.) was successfully generated, and which have led to the release of several cultivars.MethodologyUsing 96 microsatellite markers located in the nuclear and organelle genomes of rice, we investigated microsatellite stability in three typical introgression lines. Expression of a set of mismatch repair (MMR) genes and microsatellite-containing genes was also analyzed.Results/ConclusionsCompared with the recipient rice cultivar (Matsumae), 55 of the 96 microsatellite loci revealed variation in one or more of the introgression lines, and 58.2% of the altered alleles were shared by at least two lines, indicating that most of the alterations had occurred in the early stages of introgression before their further differentiation. 73.9% of the non-shared variations were detected only in one introgression line, i.e. RZ2. Sequence alignment showed that the variations included substitutions and indels that occurred both within the repeat tracts and in the flanking regions. Interestingly, expression of a set of MMR genes altered dramatically in the introgression lines relative to their rice parent, suggesting participation of the MMR system in the generation of microsatellite variants. Some of the altered microsatellite loci are concordant with changed expression of the genes harboring them, suggesting their possible cis-regulatory roles in controlling gene expression. Because these genes bear meaningful homology to known-functional proteins, we conclude that the introgression-induced extensive variation of microsatellites may have contributed to the novel phenotypes in the introgression lines.

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Urban shrinkage is currently spreading at global level. At the same time, the scale of urban shrinkage is not limited to urban agglomerations, metropolitan areas, or big cities, but begins to expand to a vast number of small towns. Over the years, the characteristics, models, and mechanisms of shrinkage in large cities have attracted the attention of scholars; however, the problem of shrinkage in small towns has not been fully discussed. In China, small towns are located at the margins of cities and are the first part of the countryside; hence, they are the link and the bridge between urban and rural areas, and a space carrier to solve the diseases of big cities and for rural rejuvenation as a whole. However, in the process of rapid urbanization, some small towns have experienced urban shrinkage, mainly through a decline in township enterprises and the deterioration of the living environment, which has restricted their role in coordinating the spatial support of urban and rural development. Therefore, a correct understanding of the shrinkage of small towns has considerable theoretical and practical guiding significance. We focused on the towns of the Jilin Province as the research unit, and combined township population, economy, land use, and employment indices to establish an urban shrinkage index, identifying the status, spatial distribution, and influencing factors of small towns shrinkage in the Jilin Province. Moreover, we analyzed the similarities and differences of small towns shrinkage between the Jilin Province and developed countries. The results show that small towns shrinkage in the Jilin Province shares similar characteristics with developed countries, as well as important differences in aspects such as population migration, low-level industrial structure, and administrative division adjustments.

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