Species-specific regulatory pathways of small RNAs play sophisticated roles in flower development in Dimocarpus longan Lour.

Flower development plays vital role in horticultural plants.Post-transcriptional regulation via small RNAs is important for plant flower development.To uncover post-transcriptional regulatory networks during the flower development in Dimocarpus longan Lour.‘Shixia’,an economically important fruit crop in subtropical regions,we collected and analyzed sRNA deep-sequencing datasets and degradome libraries Apart from identifying miRNAs and phased siRNA generating loci(PHAS loci),120 hairpin loci,producing abundant sRNAs,were identified by in-house protocols.Our results suggested that 56 miRNA-target pairs,2221-nt-PHAS loci,and 111 hairpin loci are involved in posttranscriptional gene silencing during longan reproductive development.Lineage-specific or species-specific post-transcriptional regulatory modules have been unveiled,including miR482-PHAS and miRN15.miR482-PHAS might be involved in longan flower development beyond their conserved roles in plant defense,and miRN15 is a novel miRNA likely associated with a hairpin locus(HPL-056)to regulate strigolactone receptor gene DWARF14(D14)and the biogenesis of phasiRNAs from D14.These small RNAs are enriched in flower buds,suggesting they are likely involved in post-transcriptional regulatory networks essential for longan flower development via the strigolactone signaling pathway.

Phytochemical constituents and biological activities of longan (Dimocarpus longan Lour.) fruit: a review

Longan(Dimocarpus longan Lour.),as an edible fruit and traditional Chinese medicine,has been consumed for thousands of years.Longan pulp has abundant nutritional phytochemicals such as protein,carbohydrate,vitamin C,polysaccharides,polyphenols,which shows multiple biological activities including antioxidant,immunomodulatory and antitumor effects.Longan pericarp also demonstrates biological activities because of its rich content of polysaccharides and polyphenols.This review summarizes the bioactive compounds and bioactivities of longan pulp and aims to provide comprehensive information for future development of longan as a functional health food.

Research Progress on Structure and Bioactivity of Longan Polysaccharide

Longan originates from southern China and has high nutritional and health value.Recent phytochemistry and pharmacology studies have shown that polysaccharides are a main bioactive component of longan.Longan polysaccharides possess antioxidant,anti-aging,anti-tumor,immunomodulatory,and other bioactivities.Hot-water extraction,ethanol precipitation,and ultrasonic extraction are generally used to extract water-soluble longan polysaccharides.However,the relationship between the structure and bioactivity of longan polysaccharides remains unclear,requiring further investigation.The aim of this review is to evaluate the current literature focusing on the extraction,purification,structural characterization,and biological activity of longan polysaccharides.We believe that this review would provide a useful bibliography for further innovation and a basis for using longan polysaccharides in functional food.

Absorption and Transfer of Exogenous Selenium in Longan(Dimocarpus longan Lour.) and Its Effect

Different concentrations of sodium selenite and sodium selenate were applied to leaves and roots of longan( Dimocarpus longan Lour.) to study the absorption and transfer characteristics of exogenous selenium in longan,and the effects of nitrogen and phosphorus fertilizers on the absorption of selenium in longan were discussed. This study provides a theoretical basis and reference for the research and influence on the absorption and transfer mechanism of selenium in longan and the production of selenium-enriched longan.

Genome-wide analysis of the CCCH zinc finger family in longan:Characteristic identification and expression profiles in Dimocarpus longan Lour

CCCH(C3 H) Zinc finger(Znf) transcription factors(TFs), as a novel type of Znf gene, regulate the expression of genes by binding to their mRNAs and play important roles in plant growth and development and abiotic stress resistance.Longan(Dimocarpous longan) is a tropical/subtropical fruit tree of great economic importance in Southeast Asia.However, genomic information on C3 H and their functions in longan are still unknown. In this study, a comprehensive analysis of the longan C3 H(DlC3 H) gene family was carried out. A total of 49 DlC3 H genes in three clades were identified from the longan genome database. Characteristics of the genes were analyzed with respect to gene structure,motif composition, phylogenetic tree and potential functions. The analysis of alternative splicing(AS) events suggested that AS events in DlC3 H genes were related to the transformation from longan non-embryonic to embryonic cultures.Promoter analysis indicated that most of the DlC3 H genes included cis-acting elements associated with hormones and stresses responses. Quantitative real-time PCR(qRT-PCR) analysis indicated that 26 of the 49 DlC3 Hs, which possess methyl jasmonate(MeJA) and abscisic acid(ABA) responsive cis-acting elements, showed differential expression patterns under treatment with ABA, MeJA and their endogenous inhibitors, suggesting that DlC3 Hs might be involved in the ABA and MeJA signaling pathways. The expression profiles of 17 of the 49 DlC3 Hs in non-embryonic callus and three tissues of embryonic cultures showed that only five of the 17 DlC3 Hs had the same expression trends as the FPKM trends in transcriptome data;the expression levels of DlC3 H07/14/16/36/49 in embryogenic callus and DlC3 H04/38 in globular embryos were high, suggesting that they have different functions in embryonic development. Further, we verified that DlC3 H01/03/05/11/19/39 were regulated by sRNAs by a modified 5’ RLM-RACE method. This study provides the first systematic analysis of C3 H genes in longan, and found that C3 H genes may be involved in hormone and stress responses, and somatic embryogenesis. Our preliminary investigation may provide clues to further studies on the characteristics and functions of this family in longan.

Optimization of Extraction Process for Longan(Dimocarpus longan Lour.)Leaves Using Multi-indicator Comprehensive Evaluation Method

[Objectives]This study aimed to optimize the extraction process of longan(Dimocarpus longan Lour.)leaves by multi-indicator comprehensive evaluation method.[Methods]The contents of gallic acid ethyl ester,astragalin,quercetin,luteolin and kaempferol in longan leaves were determined simultaneously by HPLC.Using the multi-indicator comprehensive evaluation method,the methanol concentration,solid to liquid ratio and extraction time for extraction of longan leaves were optimized by orthogonal test.[Results]The optimal extraction process of longan leaves are as follows:methanol concentration of 100%,solid to liquid ratio of 1∶5,and extraction time of 50 min.[Conclusions]The optimized process is simple and feasible,and it can be used to determine the contents of different ingredients in longan leaves.

An Investigation on the Relationship between Oxidative Damage and Flowering of Longan (Dimocarpus longan Loureiro)

Eight-year-old ＂Shixia＂ longan （ Dimocarpus longan Loureiro ） trees were treated under low temperature stress, oxidative stress, and natural low temperature conditions ＋ experimental agents to investigate the relationship between oxidative damage and flowering of longan. The results indicated that oxidative stress was conducive to flowering of longan, which also led to accumulation of reactive oxygen species in various tissues of longan. The detection results of reactive oxygen species, ascorbic acid content and MDA content in apical buds and leaves showed that ascorbic acid could inhibit flowering of longan, while MDA could promote flowering of longan. Therefore, there was a positive correlation between reactive oxygen species and flowering of longan.

Occurrence and Damage of Ferrisia virgata Cockerell on Longan (Dimocarpus longgana Lour.) in Guangdong Province of China

Ferrisia virgata （Cockerell） is a post with wide distribution and broad range of host plants, but apparently it has not yet known to be an important post in China. Survey on pests of longan （Dimocarpus longgana Lour. ） in Zhangjiang of Guangdong Province in 2011 found that F. virgata had caused serious damage on production of longan. The paper first reported damage status of F. virgata on longan and also preliminarily introduced field identification characterlstics and host plants of F. virgata reported.

龙眼拟茎点霉(Phomopsis longanae Chi)的生物学特性研究

龙眼拟茎点霉（Phomopsis longanae Chi）是导致采后龙眼果实腐烂的主要病原菌,研究了温度、湿度、pH值、光照、营养、越冬越夏等条件对龙眼拟茎点霉菌丝生长、产孢和孢子萌发的影响。结果表明：龙眼拟茎点霉生长适温为25℃,最适pH6~7;产生子座的最适温度为22~25℃,最适pH6,还需要一定的光照;以蔗糖、葡萄糖、可溶性淀粉和D-果糖为碳源和以蛋白胨、硫酸铵和硝酸铵为氮源的培养基最有利于龙眼拟茎点霉的生长发育;分生孢子的大量萌发要求高湿度和营养刺激,最适萌发温度25~28℃,最适pH6~7,在分生孢子器中,分生孢子的存活时间长于1年;该菌菌丝的致死温度为59℃（10 min）,分生孢子为50℃（10 min）。

Comparative Analysis on Fruit Qualities of Longan Varieties form Vietnam

[Objective] The aim was to screen longan varieties suitable for local production in Vietnam.[Method] The fruit botanical characteristics and quality characteristics of longan varieties introduced into Northern Mountainous Agriculture and Forestry Science Institute of Vietnam Academy of Agriculture Sciences were compared and analyzed.[Result] Two varieties with good general qualities including PMP6 and PHS1-1 which were suitable to be cultivated in the local area were selected.In addition,Phu Dong was the available processed germplasm resource.[Conclusion] This research will provide reference for longan production and breeding in Northern Mountainous.

Quality Detection of Fresh Longan Fruit in Hainan

[Objective] This study was conducted to investigate the fresh eating-quality of Hainan Iongan. [Methed] The quality analysis was conducted on on-season and off-season Iongan, which are main cultivars in Hainan consistent in maturity. In order to understand the quality characteristics of Hainan fresh Iongan, saccharide contents, vitamin C content, edible rate, TSS, weight of single fruit, weight per fruit cluster and pesticide residues were detected in this study. [Result] There were no significant differences in quality between on-season and off-season Iongan, and the content of TSS in off-season fruit was slightly higher than that in on-season Iongan. The two main cultivars ‘Shixia＇ and ＇Chuliang＇ in Hainan differed significantly in edible quality. The weight of single fruit and edible rate of ‘Chuliang＇ were slightly higher than those of ‘Shixia＇ Iongan, and their sucrose contents were nearly equivalent. Vitamin C and TSS contents in ‘Shixia＇ Ionganwere higher than those in ‘Chuliang＇.‘Shixia＇ had a monosaccharide content significantly higher than ‘Chuliang＇, while its sucrose content was lower than ‘Chuliang＇. Only low contents of residual cypermethrin and diflubenzuron were detected in pericarp, and the contents of the 9 pesticides in fruit flesh were all lower than their detection limits. [Conclusion] Longan fruit produced in Hainan could all be eaten safely.

A Preliminary Analysis of the Relationship between Longan Canopy Temperature and Air Temperature during Overwintering Period

[Objective] The study aimed to provide supports for developing chilling and freezing injury monitoring and disaster damage assessment of longan(Dimocarpus Longan Lour.).[Method] Based on field observation data,the relationships between longan canopy temperature and air temperature under different weather types(sunny,cloudy to sunny,cloudy,rainy,radiation chilling injury and advection chilling injury)in 2007-2008 winter were analyzed.[Result] Diurnal variations of longan canopy temperature under sunny and radiation chilling injury weather conditions were most dramatic,followed with those under cloudy to sunny condition,while variations under cloudy,rainy and advection chilling injury conditions were mild.Diurnal variations of orchard air temperature were also closely related to weather types.By using linear and curvilinear regression methods,the relationship models between longan canopy temperature and observation station air temperature were established.The models for cloudy,rainy and advection chilling injury had better effects than those for sunny,cloudy to sunny and radiation chilling injury;the models for night were better than those for daytime and the whole day.[Conclusion] To some extent,applying the relationship models between longan canopy temperature and observation station air temperature could make up the shortcoming of meteorological data which were higher than the real values.

Genome-wide identification and expression analysis of Argonaute gene family from longan embryogenic callus

Argonaute(AGO)proteins are the core of the RNA-induced gene silencing complex which regulate a wide variety of processes in plants,from organ development to abiotic stress responses.They have been identified in many plants,but little is known in longan(Dimocarpus longan Lour.),and how AGO functions in the signaling pathways in plant embryos in response to changing environmental stimuli remains unclear.In the present research,a genome-wide analysis of the AGO gene family members and their roles in somatic embryogenesis(SE),zygotic embryogenesis(ZE),tissue developmental processes,and responses to hormones,light and abiotic stress in longan were conducted.Ten longan AGO genes were identified genome-wide and divided into four clades.They were distributed on chromosomes 1,4,8,10,12,13,14,and 15,and had 2–23 introns.The expression profiling implied that DlAGOs regulated early and middle embryogenesis,as well as developmental processes of seed,flower,and stem in longan.In addition,the transcript levels of DlAGOs in response to exogenous hormones,light and abiotic stress showed differences in expression patterns.These results provide the useful information for further elucidation of RNAi-mediated gene silencing in longan embryogenic callus(EC).

Analysis of Carbon Content in Off-season Flowering and Non-flowering Longan Trees

After flower induction, some longan trees can successfully blossom and bear fruit, while others with similar tree body status can only sprout leaf buds. In order to investigate the main reason for these differences, in this study, off-season flowering and non-flowering longan trees were used as experimental materials to analyze the changes of carbon content in mature leaves, tender leaves, mature shoots, tender shoots and terminal buds of longan trees after flower induction by potassium chlorate. The result showed that carbon content played an important role in flowering process. Off-season longan trees with carbon content in mature leaves reached 50.93 mg/g could successfully blossom, but those with carbon content in mature leaves lower than 37.40 mg/g were usually difficult to blossom. In addition, the maturity of tender leaves posed great influence on flowering. Specifically, tender leaves with a higher maturity contained higher carbon content and could easily blossom, which could be used as a new indicator to evaluate flower induction in off-season longan trees.

Differences in Carbon Nutrition between On-season and Off-season Longan during the Flowering Process

Flower-bud differentiation is the most critical stage of fruit yield formation, as well as a complicated carbon transfer process. To understand the changes of carbon during the flower bud differentiation process of longan, it is very important to adopt suitable planting measures and control flowering time. This study fo- cused on the changes of sugar and starch content of on-season and off-season longan during the flowering process. The results showed that the accumulation and transformation of carben differed between on-season and off-season longan during flower-bud differentiation process ; to be specific, sugar and starch content in tissues differentiated from apical buds of on-season longan were reduced at the late flower-bud physiological differentiation stage except in leaf buds ; on the contrary, sugar and starch content in off-season longan increased at the late flower-bud physiological differentiation stage： specifically, total sugar content increased from 15.43 （ - 7 d） to 31.38 mg/g （7 d） ; starch content increased from 5.42 to 8.31 mg/g during this time, which may be relevant to the external environment or tree original metabolism damaged by potassium chlorate.

Potential roles of longan flower and seed extracts for anticancer

Polyphenol-rich plants are known to possess benefits to human health. Recent studies have revealed that many Traditional Chinese Medicines(TCMs) are rich sources of polyphenols and exhibit antioxidant and anti-inflammatory activities, and these TCMs have been shown experimentally to overcome some chronic diseases, including cancer. Longan flowers and seeds, two TCMs traditionally used for relieving pain and urinary diseases, have been revealed in our recent reports and other studies to possess rich amounts of polyphenolic species and exhibit strong anti-oxidant activity, and these could be applied for the treatment of diabetes and cancer. Herein, we review the recent findings regarding the benefits of these two TCMs in the treatment of humancancer and the possible cellular and molecular mechanisms of both substances.

Continuous Lactic Acid Production from Longan Juice by Lactobacillus casei subsp, rhamnosus TISTR 108

This research focused using novel substrate, longan Lactobacillus casei subsp, rhamnosus TISTR 108. The optimum juice as carbon source for continuous lactic acid production by medium for lactic acid production was pure longan juice with 120 g/L sugar concentration and among the different nitrogen sources were added to the longan juice （yeast extract, tryptic soy, urea, （NH4）2SO4 and NaNO3）, yeast extract had the most efficiency. Yeast extract （10 g/L） without adding minerals to longan juice could produced the maximum lactic acid concentration of 38.91 ± 0.190 g/L in 60 h and the yield of 0.460± 0.122 g/g with the productivity of 0.649± 0.002 g/Lh in 2 liters flask. Batch fermentation was conducted in 2 liters fermentor and 41.38± 0.030 g/L lactic acid was produced in 48 h with the yield of 0.398 ± 0.215 g/g and the productivity was 0.862 ± 0.001 g/L h. The continuous fermentation using 2 liters fermentor as a high productivity for lactic acid （1.091 ± 0.001 g/L h） was achieved at dilution rate （D） of 0.0685 h-1.

Immobilization of Lactobacillus rhamnosus TISTR108 on Crude Pectin of Krung Kha Mao Leaves （Cissampe/os pareira L.） to Produce Lactic Acid in Longan Juice

L-（＋）-lactic acid production was studied by immobilized Lactobacillus rhamnosus T1STR108 on crude pectin from Krung Kha Mao Leaves. Central composite design was employed to determine the maximum lactic acid production of 42.88 g L-1 in predicted model with the factors at 4.11 g L1 of pectin, 6.05 mLLl inoculum and 1.09 mm of bead diameter. Statistical analyses demonstrated very high significance for the regression model, since the F-value computed 116.09 was much higher than the tabulated F-value 2.08 for the lactic acid production at 5% level for linear and quadratic polynomial regression models. The highest experimental lactic acid production was 43.57 g L^-1 at 96 h of fermentation, 1.58% higher than the predicted value.

Indicator Analysis of Off-season Longan Flower Reversal

[Objectives] This study was conducted to analyze the internal causes of flower reversal in Longan （ Dimocarpus longan Lour.） trees. [Methods] With flowering trees and flower reversal trees as experimental materials, the variations in sugar and starch in mature leaves, tender leaves, mature branches, twigs and terminal buds after flower forcing were analyzed. [Results] During flowering process, sugar content showed the greatest difference between flowering and flower reversal trees, and the difference was the greatest in mature leaves. Trees with mature leaves having a sugar content above 44.71 mg/g were found to be more prone to flowering, while those with leaf sugar content lower than 27.80 mg/g were susceptible to flower reversal. In addition, longan trees with a higher sugar content in tender leaves were not prone to flower reversal. [Conclusions] In future, whether off-season flower forcing can be performed on longan trees could be judged through the detection of tree leaves, which is of great significance to prevention of flower reversal in off-season longan production.

Application of Ramp to Improve the Efficiency of RAPD in Longan

[ Objective] This study aimed to explore a modified method for improving the efficiency of RAPD technology. [ Method] Longans collected from Si- chuan, Fujian, Guangxi, Guangdong and Hainan were used as experimental materials. Total genomic DNA was extracted from langan leaves with modified CTAB method. 18 random primers were selected for RAPD amplification with ramp rates of 0.3 and 3.0℃/s, respectively. Effects of different ramp rates on RAPD am- plification were compared and the relationship among longan samples was analyzed. [ Result] The resolution and yield could be improved significantly by declining the ramp rate from 3.0 to 0.3℃/s. Cluster analysis showed that similarity coefficient of the five varieties of longan ranged from 0.69 to 0.76. [ Conclusion] This study had confirmed that reducing ramp rate could significantly increase the resolution and yield of RAPD technology, which had provided a new method to improve the efficiency of RAPD.