Chromosome constitution and genetic relationships of Morus spp. revealed by genomic in situ hybridization.

BACKGROUND: Mulberry (Morus spp.) is an economically important woody plant, which has been used for sericulture (silk farming) for thousands of years. The genetic background of mulberry is complex due to polyploidy and frequent hybridization events. RESULTS: Comparative genomic in situ hybridization (cGISH) and self-GISH were performed to illustrate the chromosome constitution and genetic relationships of 40 mulberry accessions belonging to 12 species and three varietas in the Morus genus and containing eight different ploidy levels. We identified six homozygous cGISH signal patterns and one heterozygous cGISH signal pattern using four genomic DNA probes. Using cGISH and self-GISH data, we defined five mulberry sections (Notabilis, Nigra, Wittiorum, and Cathayana, all contained only one species; and Alba, which contained seven closely related species and three varietas, was further divided into two subsections) and proposed the genetic relationships among them. Differential cGISH signal patterns detected in section Alba allowed us to refine the genetic relationships among the closely related members of this section. CONCLUSIONS: We propose that GISH is an efficient tool to investigate the chromosome constitution and genetic relationships in mulberry. The results obtained here can be used to guide outbreeding of heterozygous perennial crops like mulberry.

Novel polyarylether nitrile/layered bimetallic oxide/2-Methylimidazole composite membrane for efficient synergistic adsorption and degradation of organic pollutants under visible light.

The difficulty of recycling and the finite photocatalytic performance of primitive nano-photocatalysts restrict their application in wastewater purification. In this study, a multifunctional membrane with efficient synergistic adsorption and degradation performance was constructed. The nano-photocatalyst layered bimetallic oxide (LDO) was combined with the matrix membrane polyarylether nitrile (PEN) by delayed phase transition technology. The introduced 2-Methylimidazole (2-MeIm) provided a virtual electron transfer pathway between PEN and LDO and enhanced the photocatalytic performance. The results suggested that PEN/LDO/2-MeIm has outstanding removal performance to organic dyes methylene blue (MB). After three consecutive cycles, the reacted membrane can be readily recovered from the system. The MB removal rate remained high at 89.38%, suggesting that the functional membrane is eligible for recycling and reuse. Finally, based on liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) calculations, the mechanism and pathway of MB photodegradation by the PEN/LDO/2-MeIm system were proposed. Therefore, constructing PEN/LDO/2-MeIm membranes in this study may offer a novel perspective on creating eco-friendly and functional PEN-based membranes for practical use in wastewater purification.

Chromosome restructuring and number change during the evolution of Morus notabilis and Morus alba.

Mulberry (Morus spp.) is an economically important plant as the main food plant used for rearing domesticated silkworm and it has multiple uses in traditional Chinese medicine. Two basic chromosome numbers (Morus notabilis, n = 7, and Morus alba, n = 14) have been reported in the genus Morus, but the evolutionary history and relationship between them remain unclear. In the present study, a 335-Mb high-quality chromosome-scale genome was assembled for the wild mulberry species M. notabilis. Comparative genomic analyses indicated high chromosomal synteny between the 14 chromosomes of cultivated M. alba and the six chromosomes of wild M. notabilis. These results were successfully verified by fluorescence in situ hybridization. Chromosomal fission/fusion events played crucial roles in the chromosome restructuring process between M. notabilis and M. alba. The activity of the centromere was another key factor that ensured the stable inheritance of chromosomes. Our results also revealed that long terminal repeat retrotransposons were a major driver of the genome divergence and evolution of the mulberry genomes after they diverged from each other. This study provides important insights and a solid foundation for studying the evolution of mulberry, allowing the accelerated genetic improvement of cultivated mulberry species.

Molecular phylogeny of mulberries reconstructed from ITS and two cpDNA sequences.

BACKGROUND: Species in the genus Morus (Moraceae) are deciduous woody plants of great economic importance. The classification and phylogenetic relationships of Morus, especially the abundant mulberry resources in China, is still undetermined. Internal transcribed spacer (ITS) regions are among the most widely used molecular markers in phylogenetic analyses of angiosperms. However, according to the previous phylogenetic analyses of ITS sequences, most of the mulberry accessions collected in China were grouped into the largest clade lacking for phylogenetic resolution. Compared with functional ITS sequences, ITS pseudogenes show higher sequence diversity, so they can provide useful phylogenetic information. METHODS: We sequenced the ITS regions and the chloroplast DNA regions TrnL-TrnF and TrnT-TrnL from 33 mulberry accessions, and performed phylogenetic analyses to explore the evolution of mulberry. RESULTS: We found ITS pseudogenes in 11 mulberry accessions. In the phylogenetic tree constructed from ITS sequences, clade B was separated into short-type sequence clades (clades 1 and 2), and a long-type sequence clade (clade 3). Pseudogene sequences were separately clustered into two pseudogroups, designated as pseudogroup 1 and pseudogroup 2. The phylogenetic tree generated from cpDNA sequences also separated clade B into two clades. CONCLUSIONS: Two species were separated in clade B. The existence of three connection patterns and incongruent distribution patterns between the phylogenetic trees generated from cpDNA and ITS sequences suggested that the ITS pseudogene sequences connect with genetic information from the female progenitor. Hybridization has played important roles in the evolution of mulberry, resulting in low resolution of the phylogenetic analysis based on ITS sequences. An evolutionary pattern illustrating the evolution history of mulberry is proposed. These findings have significance for the conservation of local mulberry resources. Polyploidy, hybridization, and concerted evolution have all played the roles in the evolution of ITS sequences in mulberry. This study will expand our understanding of mulberry evolution.

FISH-based mitotic and meiotic diakinesis karyotypes of Morus notabilis reveal a chromosomal fusion-fission cycle between mitotic and meiotic phases.

Mulberry (Morus spp.), in family Moraceae, is a plant with important economic value. Many polyploid levels of mulberry have been determined. In the present study, the fluorescence in situ hybridization (FISH) technique was applied in Morus notabilis, using four single-copy sequences, telomere repeats, and 5S and 25S rDNAs as probes. All the mitotic chromosomes were clearly identified and grouped into seven pairs of homologous chromosomes. Three dot chromosome pairs were distinguished by the FISH patterns of the 25S rDNA probe and a simple sequence repeat (SSR2524). According to the FISH signals, chromosome length and morphology, detailed meiotic diakinesis karyotype was constructed. Interestingly, only six bivalent chromosomes were observed in diakinesis cells. The 25S rDNA probe was used to illustrate chromosome alterations. The results indicated that mitotic chromosomes 5 and 7 fused into diakinesis chromosome 5 during the meiotic phase. In mitotic cells, the fused chromosome 5 broke into chromosomes 5 and 7. A chromosomal fusion-fission cycle between the meiotic and mitotic phases in the same individual is reported here for the first time. This finding will contribute to the understanding of karyotype evolution in plants.