Marigold (Tagetes erecta L.) is an important ornamental plant with a wide variety of flower colors. Despite its economic value, few biochemical and molecular studies have explored the generation of flower color in this species. To study the mechanism underlying marigold petal color, we performed a metabolite analysis and de novo cDNA sequencing on the inbred line ‘V-01’ and its petal color mutant ‘V-01M’ at four flower developmental stages. A total of 49,217 unigenes were identified from 24 cDNA libraries. Based on our metabolites and transcriptomic analyses, we present an overview of carotenoid biosynthesis, degradation, and accumulation in marigold flowers. The carotenoid content of the yellow mutant ‘V-01M’ was higher than that of the orange inbred line ‘V-01’, and the abundances of the yellow compounds lutein, neoxanthin, violaxanthin, zeaxanthin, and antheraxanthin were significantly higher in the mutant. During flower development, the carotenoid biosynthesis genes were upregulated in both ‘V-01’ and ‘V-01M’, with no significant differences between the two lines. By contrast, the carotenoid degradation genes were dramatically downregulated in the yellow mutant ‘V-01M’. We therefore speculate that the carotenoid degradation genes are the key factors regulating the carotenoid content of marigold flowers. Our research provides a large amount of transcriptomic data and insights into the marigold color metabolome.

CRISPR/Cas9-mediated genome editing is a next-generation strategy for genetic modifications. Typically, sgRNA is constitutively expressed relying on RNA polymerase III promoters. Polymerase II promoters initiate transcription in a flexible manner, but sgRNAs generated by RNA polymerase II promoter lost their nuclease activity. To express sgRNAs in a tissue-specific fashion and endow CRISPR with more versatile function, a novel system was established in a polycistron, where miRNAs (or shRNAs) and sgRNAs alternately emerged and co-expressed under the control of a single polymerase II promoter. Effective expression and further processing of functional miRNAs and sgRNAs were achieved. The redundant nucleotides adjacent to sgRNA were degraded, and 5′- cap structure was responsible for the compromised nuclease capacity of sgRNA: Cas9 complex. Furthermore, this strategy fulfilled conducting multiplex genome editing, as well as executing neural- specific genome editing and enhancing the proportion of homologous recombination via inhibiting NHEJ pathway by shRNA. In summary, we designed a new construction for efficient expression of sgRNAs with miRNAs (shRNAs) by virtue of RNA polymerase II promoters, which will spur the development of safer, more controllable/regulable and powerful CRISPR/Cas9 system-mediated genome editing in a wide variety of further biomedical applications.

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Lethal-7 (let-7) microRNA (miRNA) serves a pivotal role in a number of physiological processes and is associated with the occurrence and development of multiple disorders such as cancer. The present study aimed to use a newly developed stem-loop strategy for reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to distinguish let-7 miRNA family members that differ by as little as a single nucleotide. For the miRNAs comprising 16 identical nucleotides at the 5′-end, different stem-loop RT primers were designed and used in RT-qPCR to assess the expression profiles of a panel of let-7 family member miRNAs in human glioblastoma U87 cells. Amplification efficiency was evaluated through correlation analysis between total RNA input and the quantification threshold values. Melting curve profiles were measured to estimate the amplification specificity of the improved stem-loop RT-qPCR compared with those of the poly(A)-tailing method. In addition, the discrimination ability of the modified stem-loop method was examined. Compared with poly(A) tailing, the modified stem-loop RT method was able to specifically reverse transcribe the diverse let-7 miRNA family members followed by accurate quantification, with a theoretical amplification efficiency of ~100%. This modified stem-loop method was able to distinguish miRNAs with a single base difference. This innovative method may be used in the clinical detection of let-7 expression levels in a variety of tumour samples, and may provide valuable data for disease diagnosis and prognostic evaluation. In addition, this method may offer a new avenue for developing particular stem-loop approaches in measuring other miRNAs with little discrepancy.