Volatile constituents of yuzu ( Citrus junos Sieb. ex Tanaka) peel oil: A review

Identification of odorant receptors of Tribolium confusum in response to limonene repellent activity

Tribolium confusum is an important storage pest showing significant resistance to various chemical pesticides, development of botanical pesticides is an effective strategy to resolve above problem and decrease utilization of chemical pesticides. Present study attempts to explore the molecular mechanism about the repellent activity of limonene. When treatment concentration of limonene was 200.00 μg/cm2, the repellent level remained at grade V after 24 hours. Our study showed that limonene could be distinguished by T. confusum antenna with a maximal electroantennography test value of 0.90 mV. Simultaneously, 88 upregulated and 98 downregulated genes were sequenced in limonene-repellent T. confusum, and RT-qPCR analysis showed that four down-regulated and one up-regulated OR genes play an important role in the response to limonene. The repellent rate was decreased by 22.13% mediated with a knockdown of dsTconOR93, while the EAG value of the female and male adults was reduced to 0.26 mV (49.06%) and 0.20 mV (54.05%), respectively. In conclusion, limonene had a strong repellent activity against T. confusum and TconOR93 gene was determined to be a major effector in perception of limonene. This study provides a basis for the development of limonene as a novel botanical pesticide for the control to storage pests, which will reduce the utilization of chemical pesticides and postpone the development of resistance.

The draft genome and multi-omics analyses reveal new insights into geo-herbalism properties of Citrus grandis 'Tomentosa'

Citrus grandis 'Tomentosa' (CGT) (Huajuhong, HJH) is a widely used medicinal plant, which is mainly produced in Guangdong and Guangxi provinces of South China. Particularly, HJH from Huazhou (HZ) county of Guangdong province has been well-regarded as the best national product for geo-herbalism. But the reasons for geo-herbalism property in HJH from HZ county remains a mystery. Therefore, a multi-omics approach was applied to identify the nature of the geo-herbalism in CGT from three different regions. The comprehensive screening of differential metabolites revealed that the Nobiletin content was significantly different in HZ region compared to other regions, and could be employed as a key indicator to determine the geo-herbalism. Furthermore, the high-quality genome (N50 of 9.12 Mb), coupled with genomics and transcriptomics analyses indicated that CGT and Citrus grandis are closely related, with a predicted divergence time of 19.1 million years ago (MYA), and no recent WGD occurred in the CGT, and the bioactive ingredients of CGT were more abundant than that of Citrus grandis. Interestingly, Nobiletin (Polymethoxyflavones) content was identified as a potential indicator of geo-herbalism, and O-methyltransferase (OMT) genes are involved in the synthesis of Polymethoxyflavones. Further multi-omics analysis led to the identification of a novel OMT gene (CtgOMT1) whose transient overexpression displayed significantly higher Nobiletin content, suggesting that CtgOMT1 was involved in the synthesis of Nobiletin. Overall, our findings provide new data resources for geo-herbalism evaluation, germplasm conservation and insights into Nobiletin biosynthesis pathways for the medicinal plant C. grandis 'Tomentosa'.

Chemical Variability of Peel and Leaf Essential Oils in the Citrus Subgenus Papeda (Swingle) and Few Relatives

The Papeda Citrus subgenus includes several species belonging to two genetically distinct groups, containing mostly little-exploited wild forms of citrus. However, little is known about the potentially large and novel aromatic diversity contained in these wild citruses. In this study, we characterized and compared the essential oils obtained from peels and leaves from representatives of both Papeda groups, and three related hybrids. Using a combination of GC, GC-MS, and ¹³C-NMR spectrometry, we identified a total of 60 compounds in peel oils (PO), and 76 compounds in leaf oils (LO). Limonene was the major component in almost all citrus PO, except for C. micrantha and C. hystrix, where β-pinene dominated (around 35%). LO composition was more variable, with different major compounds among almost all samples, except for two citrus pairs: C. micrantha/C. hystrix and two accessions of C. ichangensis. In hybrid relatives, the profiles were largely consistent with their Citrus/Papeda parental lineage. This high chemical diversity, not only among the sections of the subgenus Papeda, but also between species and even at the intraspecific level, suggests that Papeda may be an important source of aroma diversity for future experimental crosses with field crop species.