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Ribosomal DNA (rDNA) is an excellent cytogenetic marker owing to its tandem arrangement and high copy numbers. However, comparative studies have focused more on the number of rDNA site variations within the Chrysanthemum genus, and studies on the types of rDNA sites with the same experimental procedures at the species levels are lacking. To further explore the number and types of rDNA site variations, we combined related data to draw ideograms of the rDNA sites of Chrysanthemum accessions using oligonucleotide fluorescence in situ hybridization (Oligo-FISH). Latent variations (such as polymorphisms of 45S rDNA sites and co-localized 5S-45S rDNA) also occurred among the investigated accessions. Meanwhile, a significant correlation was observed between the number of 5S rDNA sites and chromosome number. Additionally, the clumped and concentrated geographical distribution of different ploidy Chrysanthemum accessions may significantly promote the karyotype evolution. Based on the results above, we identified the formation mechanism of rDNA variations. Furthermore, these findings may provide a reliable method to examine the sites and number of rDNA variations among Chrysanthemum and its related accessions and allow researchers to further understand the evolutionary and phylogenetic relationships of the Chrysanthemum genus.

Whole genome duplication, associated with the induction of widespread genetic changes, has played an important role in the evolution of many plant taxa. All extant angiosperm species have undergone at least one polyploidization event, forming either an auto- or allopolyploid organism. Compared with allopolyploidization, however, few studies have examined autopolyploidization, and few studies have focused on the response of genetic changes to autopolyploidy. In the present study, newly synthesized C. nankingense autotetraploids (Asteraceae) were employed to characterize the genome shock following autopolyploidization. Available evidence suggested that the genetic changes primarily involved the loss of old fragments and the gain of novel fragments, and some novel sequences were potential long terminal repeat (LTR) retrotransposons. As Ty1-copia and Ty3-gypsy elements represent the two main superfamilies of LTR retrotransposons, the dynamics of Ty1-copia and Ty3-gypsy were evaluated using RT-PCR, transcriptome sequencing, and LTR retrotransposon-based molecular marker techniques. Additionally, fluorescence in situ hybridization(FISH)results suggest that autopolyploidization might also be accompanied by perturbations of LTR retrotransposons, and emergence retrotransposon insertions might show more rapid divergence, resulting in diploid-like behaviour, potentially accelerating the evolutionary process among progenies. Our results strongly suggest a need to expand the current evolutionary framework to include a genetic dimension when seeking to understand genomic shock following autopolyploidization in Asteraceae. [ABSTRACT FROM AUTHOR]

• Bacillus velezensis and Pseudomonas aeruginosa were isolated and identified from rhizosphere soils obtained from different chrysanthemum production bases. • PGPRs significantly enhance the growth and nutrient accumulation of chrysanthemum. • Co-inoculation with both PGPRs demonstrates enhanced plant growth and quality in chrysanthemums compared to single PGPR strain inoculation. However, it appears that Bacillus velezensis plays a dominant role in growth. • PGPRs regulate metabolic pathways and growth hormone signaling pathways in chrysanthemums. • PGPR induces gene expression in cellular metabolism, signal transduction, and probiotic substance synthesis. The inoculation of plants with plant growth-promoting rhizobacteria (PGPR) has been increasingly discussed as a way to sustainably promote plant growth and soil health. Although some promising results have been achieved in the laboratory, the applications of microbial inoculants in chrysanthemum production greenhouses and co-inoculation with PGPRs in ornamental planting systems have been less investigated. Here, greenhouse experiments were conducted to study the integrated effect of bioagents (Bacillus velezensis and Pseudomonas aeruginosa) on chrysanthemum nutrient use efficiency, plant growth, and quality. The growth-promoting mechanisms were further elucidated by transcriptome analysis. Co-inoculation with the two PGPRs increased the absorption and utilization of nitrogen, phosphorus, and potassium. The quality and growth of chrysanthemum were significantly higher than those of single PGPR inoculation or soil conditioner application. Transcriptome analysis revealed that differentially expressed genes (DEGs) were co-expressed at 30, 60, and 90 days after chrysanthemum co-inoculation with the two PGPRs. DEGs were primarily enriched in metabolic and signal transduction pathways. PDC encoding pyruvate decarboxylase in the glycolysis pathway and SAUR32 and SAUR36 encoding auxin were upregulated in chrysanthemum during the PGPRs inoculation period. Notably, the transcription factors WRKY70 and BHLH35 belonging to signal transduction and defense responses were both upregulated, demonstrating that chrysanthemum system and disease resistance were activated. The results of this study could help to elucidate the mechanism of 2 PGPRs on chrysanthemum growth and development at the transcriptome level, which could lay a theoretical foundation for the highly efficient cultivation of cut chrysanthemum "Qinhuai Yulian". [ABSTRACT FROM AUTHOR]

With water shortage worldwide, seeking drought resistance genes are of great value for molecular breeding. Here, we isolated a homologous AtSCL4/7 subfamily gene of GRAS transcription factor family from chrysanthemum and designated it as CmSCL4. CmSCL4 was responded to 20% PEG6000 treatment and its heterologous expression improved drought tolerance by up-regulating ABA signaling genes AtABI3 and AtABI4 in Arabidopsis. Moreover, the cotyledon greening rate, early seedling development and stomatal aperture of transgenic Arabidopsis are hypersensitivity to external ABA treatment. Meanwhile, overexpression and chimeric repression of CmSCL4 in chrysanthemum also conferred the increased or decreased drought tolerance and corresponding changes of the expression of CmABI4. Yeast two-hybrid screening of the cDNA library of chrysanthemum by CmSCL4 identified a MYB transcription factor as an important candidate partner, which was named as CmR1MYB1 hereafter. The interaction between CmSCL4 and CmR1MYB1 was further verified by in vitro pull-down, in vivo BiFC and Co-IP assays. CmR1MYB1 and CmSCL4 had similar expression patterns under 20% PEG6000 treatment. Heterologous expression of CmR1MYB1 in Arabidopsis also facilitated the expression levels of AtABI3 and AtABI4 , resulted in the improved drought tolerance. These results demonstrated that CmSCL4 cooperates with CmR1MYB1 to modulate the dehydration tolerance of chrysanthemum, at least partially through the regulation of ABA-responsive genes. • This study describes the identification of a GRAS transcription factor CmSCL4 in chrysanthemum. • Overexpression of CmSCL4 improves drought resilience in both chrysanthemum and Arabidopsis by regulating ABA signaling pathway. • CmSCL4 interacts with the MYB transcription factor CmR1MYB1 to synergistically modulate drought adaptation in chrysanthemum. [ABSTRACT FROM AUTHOR]