[Fruit variation and geographical distribution of citron].

The ripe dried fruit of citron(Citrus medica) is one of the important sources of Chinese herb Citri Fructus. At the same time, it is also grown for edible and ornamental uses. There are many species and abundant genetic variation. To clarify the intraspecific variation and resource distribution of citron, this study investigated the variation in 11 citron fruits, basically covering the main species in China, including Xiaoguo citron(C. medica var. ethrog), Goucheng(C. medica var. yunnanensis), Muli citron(C.medica var. muliensis), Dehong citron(C.medica×Citrus spp.), Fuzhou citron(C.medica×C.grandis?), Mawu(C.medica×C.grandis?), Cangyuan citron, Binchuan citron, Sweet citron, Big citron, and Small citron. The natural communities of citron were proved to be mainly distributed in the southwestern and western Yunnan and southeastern Tibet of China, with Yunnan, Sichuan, Guangxi, Chongqing, Hubei, and Zhejiang identified as the main production areas. Citron has also been widely grown in India, the Mediterranean region, and the Caribbean coast countries. The field investigation revealed the large-scale intraspecific variation of citron fruits. Most of the fruits are oval-like or sphere-like in shape. The fruits are green when raw and yellow when ripe, with oil cell dots on the skin, stripe-likes running from top to bottom, and bulge at the top. Usually, in the smaller citron fruits, the pulp and juice vesicles are better developed and the central columella is tighter. By contrast, the juice vesicles and central columella in larger fruits became more vacant, with carpels visible, and the apex segregation and development of the carpels is one of the reasons for variation. These variations should be given top priority in the future variety selection and breeding, and the quality differences of different citron species and their mechanisms should be further studied. In particular, variety selection and classification management according to their medicinal or edible purposes will provide scientific and technological supports for the orderly, safe, and effective production of citron products consumed as food and medicine.

Transcriptome and Metabolome Comparison of Smooth and Rough Citrus limon L. Peels Grown on Same Trees and Harvested in Different Seasons.

Background: Farmers harvest two batches fruits of Lemons (Citrus limon L. Burm. f.) i.e., spring flowering fruit and autumn flowering fruit in dry-hot valley in Yunnan, China. Regular lemons harvested in autumn have smooth skin. However, lemons harvested in spring have rough skin, which makes them less attractive to customers. Furthermore, the rough skin causes a reduction in commodity value and economical losses to farmers. This is a preliminary study that investigates the key transcriptomic and metabolomic differences in peels of lemon fruits (variety Yuning no. 1) harvested 30, 60, 90, 120, and 150 days after flowering from the same trees in different seasons. Results: We identified 5,792, 4,001, 3,148, and 5,287 differentially expressed genes (DEGs) between smooth peel (C) and rough peel (D) 60, 90, 120, and 150 days after flowering, respectively. A total of 1,193 metabolites differentially accumulated (DAM) between D and C. The DEGs and DAMs were enriched in the mitogen-activated protein kinase (MAPK) and plant hormone signaling, terpenoid biosynthesis, flavonoid, and phenylalanine biosynthesis, and ribosome pathways. Predominantly, in the early stages, phytohormonal regulation and signaling were the main driving force for changes in peel surface. Changes in the expression of genes associated with asymmetric cell division were also an important observation. The biosynthesis of terpenoids was possibly reduced in rough peels, while the exclusive expression of cell wall synthesis-related genes could be a possible reason for the thick peel of the rough-skinned lemons. Additionally, cell division, cell number, hypocotyl growth, accumulation of fatty acids, lignans and coumarins- related gene expression, and metabolite accumulation changes were major observations. Conclusion: The rough peels fruit (autumn flowering fruit) and smooth peels fruit (spring flowering fruit) matured on the same trees are possibly due to the differential regulation of asymmetric cell division, cell number regulation, and randomization of hypocotyl growth related genes and the accumulation of terpenoids, flavonoids, fatty acids, lignans, and coumarins. The preliminary results of this study are important for increasing the understanding of peel roughness in lemon and other citrus species.

Characterization of the complete chloroplast genome of 'Yunning No.1' lemon (Citrus limon).

'Yunning No.1' lemon, a mutant of Eureka lemon, is originally found in Yunnan province of China and is the main cultivated lemon variety there. In this study, we assembled and annotated its chloroplast genome using Illumina Hiseq-2500 whole genome re-sequencing data. Its chloroplast genome is 160,141 bp in size, containing a 87,754 bp large single copy region, a 18,385 bp small single copy region and a pair of 27,001 bp inverted repeat region. Like many citrus species, 114 unique genes (including 80 protein-coding genes, 30 tRNAs and 4 rRNAs) could be identified from the chloroplast genome of 'Yunning No.1'. Phylogenetic analysis revealed that the 'Yunning No.1' chloroplast genome was closest to Citrus maxima.

Characterization of the complete chloroplast genome of Yuanjiang wild Ichang papeda (Citrus cavaleriei) in China.

Ichang papeda (Citrus cavaleriei) is an endemic perennial plant in China. In this study, we assembled and annotated the complete chloroplast genome of Yuanjiang wild Ichang papeda using Illumina Hiseq-2500 sequencing data. The chloroplast genome is constituted of 160,996 bp, containing a 87,634 bp large single-copy region, a 18,762 bp small single-copy region, and a pair of 27,300 bp inverted repeat regions. The chloroplast genome contains 114 unique genes, including 80 protein-coding genes, 30 tRNAs and 4 rRNAs. Phylogenetic analysis showed that the relationship between the chloroplast gennomes of C. cavaleriei and C. reticulata is the closest, which consistently support their chloroplast relationships.

Characterization of the complete chloroplast genome of Citrus hongheensis, a key protected wild plant in Yunnan province of China.

Citrus hongheensis is a key protected wild plant endemic to the Honghe river region in southeastern Yunnan, China. In the present study, its chloroplast genome was successfully assembled and annotated based on the Illumina Hiseq-2500 whole genome re-sequencing data. The chloroplast genome is 160,275 bp in size. Its large single copy region, small single copy region and inverted repeat region is 87,886 bp, 18,387 bp and 27,001 bp, respectively. Totally, 114 unique genes, including 80 protein-coding genes, 30 tRNAs and 4 rRNAs, were identified from the C. hongheensis chloroplast genome. According to the phylogenetic analysis result, the relationship between the chloroplast genome of C. hongheensis and C. maxima was found to be the closest.