Root rot is a prevalent soil-borne fungal disease in citrus. Citron C-05 (Citrus medica) stands out as a germplasm within Citrus spp. due to its complete resistance to citrus canker and favorable characteristics such as single embryo and easy rooting. However, Citron C-05 was found to be highly susceptible to root rot during cultivation, with the specific pathogens previously unknown. In this study, four candidate fungal species were isolated from Citron C-05 roots. Sequence analysis of ITS, EF-1α, RPB1, and RPB2 identified two Fusarium solani strains, Rr-2 and Rr-4, as the candidates causing root rot in Citron C-05. Resistance tests showed these two pathogens increased root damage rate from 10.30% to 35.69% in Citron C-05, sour orange (Citrus aurantium), sweet orange (Citrus sinensis) and pummelo (Citrus grandis). F. solani exhibited the weak pathogenicity towards trifoliate orange (Poncirus trifoliata). DAB staining revealed none of reddish-brown precipitation in the four susceptible citrus germplasm after infection with F. solani, while trifoliate orange exhibited significant H2O2 accumulation. Trypan blue staining indicated increased cell death in the four susceptible citrus germplasm following infection with these two pathogens but not in trifoliate orange. These findings provide a comprehensive understanding of citrus root rot and support future research on the mechanisms of root rot resistance in citrus.

Ponkan (Citrus reticulata Blanco), renowned for its sensory quality and ease of peeling, is a widely cultivated mandarin in China. However, like most commercial citrus cultivars, it is susceptible to citrus canker and Huanglongbing (HLB). Polyploid breeding may be a useful way to identify resistant or tolerant varieties. In this study, we obtained 1 060 seeds from six pollination combinations using ‘Xinnv’ ponkan and its bud mutation ‘Zaomi’ as parents. Among these, 876 seeds were classified as normal and 184 as small. Twenty-four tetraploids and one chimera were identified from progeny populations by flow cytometry. The polyploid frequency varied among combinations, with the highest rate (7.89%) observed in small seeds from open-pollinated ‘Zaomi’, compared to 1.55% to 4.76% in other groups. Morphological and microscopic analyses revealed that tetraploid progeny displayed increased leaf thickness, epidermal cells, and stomatal apparatus, whereas stomatal density was reduced compared with diploid lines. In vitro and in vivo evaluations for citrus canker tolerance demonstrated that lines #007, #315, and #369 exhibited reduced lesion area, lesion density, and Xanthomonas citri subsp. Citri content at 7 days post-inoculation relative to the diploid control ‘Zaomi’. Regarding HLB evaluation, tetraploid line #331 exhibited a lower titer of Candidatus Liberibacter asiaticus than the diploid control and maintained superior growth at 6 months post-inoculation, evidenced by a 96.3% increase in leaf area and a 48% increase in SPAD value. These novel tetraploid ponkan germplasms possess enhanced disease tolerance and represent valuable resources for future citrus breeding programs.

The pH plays a key role in the growth and colonization of plant pathogens as well as the onset and progression of the symptoms they cause within the host. Plants may quickly alter their apoplastic pH (pHapo) to protect themselves against infection. However, pathogens can also alter the pH of their ambient environment to promote their own growth. Citrus canker is a serious plant disease caused by Xanthomonas citri subsp. citri (Xcc). This Gram-negative aerobic rod is usually cultured in Luria-Bertani (LB) medium at pH 7. However, little is known about the changes in pH both in this medium as Xcc grows and in the leaf apoplast in response to Xcc infection and colonization. Moreover, the differences in leaf apoplast pH between Xcc-resistant and Xcc-susceptible citrus genotypes are also unknown. Here, Xcc grew well in liquid LB medium at initial pH 6-8 and the pathogen altered the medium pH to 6.8 +/- 0.4. Xcc growth declined at pH 5 and was zero at pH 3, 4, 9, and 10. In susceptible sweet orange infected with Xcc inoculum, canker symptoms were inhibited at pH 3, 4, and 10 but did not differ in the range of pH 5-9. As expected, canker symptoms were absent at all inoculum pH in the resistant Citron C-05. For both genotypes, Xcc only grew well in the leaves exposed to pH 5-8 inoculums. At four days post-inoculation (4 dpi), the foliar pHapo of resistant Citron C-05 had rapidly declined from 5.6 to 4.4. At 2 dpi, the pHapo of susceptible sweet orange had rapidly increased from 5.6 to 6.7, Xcc grew quickly, and canker symptoms appeared. Plasma membrane (PM) H & thorn;-ATPase activation with fusicoccin (FC) acidified the apoplast and upregulated the pathogenesis-related genes (PRs) in the sweet orange leaves. Hence, Xcc colonization and canker development were inhibited. The results of this study revealed that apoplastic acidification is implicated in the resistance of Citron C-05 to Xcc infection and provided insight into the association between pHapo regulation and resistance to bacterial invasion in

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a globally quarantine disease infecting nearly all Citrus cultivars. Citron C-05 has been identified with complete and active resistance to Xcc. However, the mechanism underlying Citron C-05’s resistance to Xcc remains elusive. We identified a gene cluster on chromosome 8 of the citrus genome comprising five pathogenesis-related 4-like genes. PR4A was upregulated in Citron C-05 leaves under Xcc infection, exhibiting the highest expression among these PR4-like genes. In addition, PR4A expression was higher in leaves of disease-resistant genotypes than susceptible genotypes under Xcc invasion. Bimolecular fluorescence complementation (BiFC) and Split-Luc assays indicated that CmWRKY75, a positive regulator of PR4A, interacted with pthA4 and upregulated expression of PR4A in Citron C-05 leaves. Regulatory function for the expression of CmPR4A was localized to a 516-nucleotide region upstream of the translational start site, which was designated ProCmPR4A-P516. Transient overexpression of CmPR4A improved resistance to Xcc in sweet orange, and three transgenic lines of OE-CmPR4A exhibited resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) in Arabidopsis. Furthermore, CmSMU2 was identified through yeast two-hybrid library using CmPR4A as bait, BiFC and Split-Luc assays further verified their interaction. Transient overexpression of CmSMU2 in sweet orange increased resistance to Xcc. Co-expression of CmSMU2 and CmPR4A enhanced accumulation of reactive oxygen species compared to CmSMU2 or CmPR4A, indicating that they may synergistically enhance resistance to Xcc in citrus. These findings lay the groundwork for a theoretical analysis of the mechanism underlying the resistance of Citron C-05 against citrus canker.

Citrus canker is a devastating disease caused by Xanthomonas citri subsp. citri (Xcc), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene CsLOB1, resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to Xcc remains elusive. This study identified CsCEL20 as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after Xcc infection. A total of 69 cellulase genes were retrieved within the Citrus sinensis genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of CsCEL8, CsCEL9, CsCEL20, and CsCEL26 were induced by Xcc invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, CsCEL20 exhibited the highest expression level, with an over 430-fold increase following Xcc infection. Additionally, RT-qPCR analysis confirmed that CsCEL20 expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon Xcc invasion, but not in resistant genotypes (Citron C-05, Aiguo citron, American citron). A Single-Nucleotide Polymorphism (SNP) at -423 bp was identified in the CEL20 promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, CsCEL20 expression was upregulated in CsLOB1-overexpression transgenic lines compared to the wild type. Dual-luciferase reporter assays indicated that CsLOB1 can target the -505 bp to -168 bp region of CsCEL20 promoter to trans-activate its expression. These findings suggest that CsCEL20 may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of Xcc-resistant citrus genotypes.

Iron is an essential nutrient for all organisms. Feruloyl-COA 6-hydroxylase 1 (F6'H1) plays a pivotal role in iron uptake in plant roots by catalyzing the biosynthesis of iron-mobilizing scopoletin, a secondary metabolite also possessing antimicrobial activity. However, it remains unclear whether F6'H1-mediated iron uptake affects plant resistance to foliar pathogens and how such a process might be regulated. Here, we show that enhanced expression of 2-oxoglutarate-dependent dioxygenases 2 (CmOGD2), a homolog of F6'H1 in Citron C-05 (Citrus medica L.), confers resistance to citrus canker caused by Xanthomonas citri subsp. citri (Xcc). CmOGD2-mediated pathogen resistance is achieved by promoting iron uptake and the accumulation of reactive oxygen species (ROS), which likely results in ferroptosis. Furthermore, CmOGD2 interacts with the enolase CmENO2 to destabilize CmZAT10.1, a transcriptional activator of CmOGD2, thereby forming a negative feedback loop that limits CmOGD2 expression. Notably, the Xcc effector pthA4 interferes with the CmOGD2-CmENO2 interaction, likely via a decoy mechanism, leading to CmZAT10.1 accumulation. These findings reveal complex regulatory mechanisms underlying the critical role of CmOGD2 in mediating Xcc resistance through iron- and ROS-dependent ferroptosis.

BACKGROUND:Citrus canker is a significant bacterial disease caused by Xanthomonas citri subsp. citri (Xcc) that severely impedes the healthy development of the citrus industry. Especially when citrus fruit is infected by Xcc, it will reduce or even lost its commercial value. However, due to the prolonged fruiting cycle and intricate structure, much less research progress had been made in canker disease on fruit than on leaf. In fact, limited understanding has been achieved on canker development and the response to Xcc infection in fruit.RESULTS:Herein, the progression of canker disease on sweet orange fruit was tracked in the field. Results indicated that typical lesions initially appear on the sepal, style residue, nectary disk, epicarp, and peduncle of young fruits after petal fall. The susceptibility of fruits to Xcc infection diminished as the fruit developed, with no new lesions forming at the ripening stage. The establishment of an efficient method for inoculating Xcc on fruit as well as the artificial inoculation throughout the fruit's developmental cycle clarified this infection pattern. Additionally, microscopic observations during the infection process revealed that Xcc invasion caused structural changes on the surface and cross-section of the fruit.CONCLUSIONS:An efficient system for inoculation on citrus fruit with Xcc was established, by which it can serve for the evaluation of citrus germplasm for canker disease resistance and systematic research on the interactions between Xcc and citrus fruits.

The citrus cultivar ‘Local Juhong’, which has historically been used as a traditional Chinese medicinal material, originated in Yuanjiang County, Hunan Province.Its parental type and genetic background are indistinct as of yet. Morphological observation shows that ‘Local Juhong’ has a slight oblateness in fruit shape, a relatively smooth pericarp, a fine and slightly raised oil vacuole, and an inward concave at the blossom end. The tree form and fruit and leaf morphology of ‘Local Juhong’ are similar to those of ‘Huangpi’ sour orange. To reveal the genetic background of ‘Local Juhong’, 21 citrus accessions were evaluated using nuclear and chloroplast SSR markers and whole-genome SNP information. ‘Local Juhong’ was grouped with mandarins and sub-grouped with ‘Miyagawa Wase’ and ‘Yanxi Wanlu’ in a nuclear SSR analysis, which indicated that its pollen parent might be mandarins. It was closely clustered with orange and pummelo in the chloroplast SSR analysis. The genomic sequence similarity rate of ‘Local Juhong’ with mandarin and pummelo heterozygosity was 70.88%; the main part was the heterozygosity, except for the unknown (19.66%), mandarin (8.73%), and pummelo (3.9%) parts. Thus, ‘Local Juhong’ may be an F1 hybrid with pummelo as the female parent and mandarin as the male parent, sharing sisterhood with ‘Huangpi’ sour orange.

Seedless is a highly valued commercial characteristic in the citrus industry, both for fresh consumption and for processed markets. In this study, the ‘Succari Sweet Orange’ (WT) and its seedless mutant ‘Juxiangyuan’ (MT), which originated from a bud mutation, were selected to study the formation of a citrus seedless phenotype. Microscopic analysis of MT’s floral organs, including anther and ovary cross-sections, provides insights into its seedless phenotype compared to the original seeded cultivar. Additionally, pollen features, viability, and in vitro germination were examined to determine the cause of seedlessness. MT exhibited significant developmental deformities in both male and female gametes, with pollen grain analysis indicating a high rate of deformity (41.48%), low viability (9.59%), and minimal in vitro germination (9.56%). Hybridization experiments were conducted to assess male and female sterility and pollen incompatibility. Both WT and MT exhibited parthenocarpic development. Notably, MT fruit produced with an average of 3.51 seeds pollinated to WT, despite severe pollen abortion of MT. MT, however, produced seedless fruit through self-breeding or cross-breeding with other varieties, demonstrating stable female sterility. Despite reduced pollen quantity and viability in the seedless mutant ‘Juxiangyuan’, its seedlessness primarily stems from female sterility. This study contributed to a deeper understanding of seedless formation in ‘Juxiangyuan’ and provided valuable information relevant to its commercial cultivation.

Citrus bacterial canker disease, caused by Xanthomonas citri subsp. citri (Xcc), poses a significant global threat to the citrus industry. Lateral organ boundaries 1 (Lob1) is confirmed as a citrus susceptibility gene that induces pathogenesis by interaction with the PthA4 effector of Xcc. Citron C-05 (Citrus medica) is a Citrus genotype resistant to Xcc. However, there is little information available on the regulation of Lob1 in resistant genotypes, which is important for the breeding of citrus cultivars resistant to canker disease. This study aimed to identify upstream regulatory factors of Lob1 in Citron C-05 and to investigate its function in disease resistance. ‘Bingtang’ sweet orange (C. sinensis), a susceptible genotype, was utilized as the control. cDNA yeast libraries of Xcc-induced Citron C-05 and ‘Bingtang’ sweet orange were constructed. The capacities of ‘Bingtang’ and Citron C-05 were 1.896 × 107 and 2.154 × 107 CFU, respectively. The inserted fragments ranged from 500 to 2000 bp with a 100% recombination rate. The promoter of Lob1 was segmented into two pieces and the P1 fragment from both genotypes was used to construct a bait yeast (PAbAi-CsLob1-P1; PAbAi-CmLob1-P1). Through library screening with the bait yeast, upstream regulators interacting with the Lob1-P1 promoter were identified and then validated using Y1H and dual-luciferase tests. The expression analysis of the three transcript factors indicated that RMA3 was upregulated by inoculation with Xcc in the resistant Citron C-05, but not in the susceptible sweet orange. The overexpression of CsRMA3 in ‘Bingtang’ sweet orange led to reduced canker symptoms, with a significantly lower pathogen density in the leaves following Xcc inoculation. When CmRMA3 was silenced by virus-induced gene silencing (VIGS) in Citron C-05, typical canker symptoms appeared on the CmRMA3-silenced leaves at 15 days post-inoculation with Xcc. Further expression analyses revealed that the CmRMA3 transcription factor suppressed the expression of Lob1. These results suggest that RMA3 participates in the resistant reaction of Citron C-05 to Xcc infection, and such a response might be in relation to its suppression of the expression of the pathogenic gene Lob1.

In order to understand the genetic diversity of germplasm resources of kumquats in Guangxi, 14 kumquat germplasm resources in Guangxi and 12 accessions from other provinces were analyzed by using SRAP markers. In total, 19 primer pairs with high stability, good reproducibility, and high polymorphism were chosen for analysis of all 26 kumquat genotypes. Among the 104 amplified bands, 90 (86.54%) were polymorphic. SRAP markers were analyzed by employing Principal Coordinate Analysis, Population Structure Analysis, and Hierarchical Cluster Analysis (UPGMA). The classification results showed that the 26 kumquat germplasm resources could be divided into 5 groups, including cultivated kumquat, intergeneric hybrid, wild kumquat from other provinces, wild kumquat, and hybrid kumquat from Guangxi. The Guangxi kumquat germplasm had high genetic diversity, and were clearly divided into three groups: cultivated kumquat, wild kumquat, and hybrid kumquat. Additionally, the eight cultivated kumquat varieties in Guangxi were further divided into two subgroups. Wild kumquat in Guangxi or in other provinces belonged to different groups; meanwhile, the Guangxi kumquat hybrid formed an independent group, thus indicating that Guangxi wild kumquat and hybrid kumquat possess certain specificity, or they possibly belong to different species. Among the tested 26 kumquat accessions, 23 unique genotype-specific SRAP markers were detected for 14 kumquat genotypes, which were positively identified. For the remaining 12 accessions without genotype-specific markers, they were distinguished by various combinations of markers. These results may have certain importance for kumquat genetic research and cultivar selection.

为探究辐射诱变冰糖橙果实提早着色性状的遗传变异,果实着色与糖酸内在品质表现,以及辐射诱变冰糖橙是否为早熟突变体,以突变体与对照冰糖橙为材料,对比分析春梢长度、春梢叶片、花器官、果实大小、果皮颜色转变、主要物候期等性状和特性的变化,应用分子标记鉴定遗传变异,比较两者果实中可溶性固形物、可滴定酸、固酸比的变化以及蔗糖和柠檬酸代谢相关基因的表达.结果表明,与对照冰糖橙相比,突变体春梢显著变短,成熟时果实较大,果皮和果肉提前15 d转色成橙黄色和橙色,主要物候期提早2～5d,插入或缺失(InDel)标记和简单序列重复(SSR)标记引物扩增都存在差异条带,突变体发生了遗传改变.早熟突变体果实外观颜色与内在品质在花后190d同步达到正常成熟度,可溶性固形物、可滴定酸及固酸比分别为14.53°Brix、0.46％和31.59,表现为低酸、降酸早、固酸比值高,比对照提早15 d成熟.蔗糖和柠檬酸的合成、降解、转运相关基因的表达分析结果表明,早熟突变体蔗糖合成多、转运早,柠檬酸合成少、降解快、贮运少,与果实品质表现低酸、降酸早、固酸比高基本吻合.综上,辐射诱变突变体发生了植物性状、生物特性、DNA的遗传改变,果实降酸早、含酸低、固酸比高,11月上旬着色成熟.研究结果为该突变体的进一步选育和登记早熟冰糖橙新品种奠定了基础.

In order to investigate the genetic mechanism of citron in resistance against citrus canker disease（Xanthomonas citri subsp.citri,Xcc）,in this study,the susceptible variety Red pomelo was crossed with the resistant genotype American citron and F 1 hybrids were obtained.F 2 progeny was further gained by self-crossing the F 1 plants.Resistance identification wan performed on the F 1 hybrid plants by in vivo inoculation of Xcc.All the F 2 plants were in vitro inoculated and 225 F 2 plants were successively identified for the resistance by in vivo inoculation.Bacterial quantification was conducted on some of the F 2 plants following the inoculation with Xcc.The results from in vivo inoculation of F 1 plants indicated that all F 1 hybrids were susceptible,and no segregation between resistance and susceptibility was observed on the F 1 progeny.In vitro identification of 253 F 2 plants showed that 76 plants were resistant and 177 were susceptible.The results of in vivo inoculation on 225 F 2 plants demonstrated that 72 plants were susceptible,with symptoms similar to those of the susceptible variety Bingtang sweet orange,118 slightly less susceptible than Bingtang sweet orange,but similar to those of the susceptible parent Red pomelo;10were resistant,similar to the resistant parent American citron and four were resistant as the resistant genotype citron C-05.In addition,the symptoms of 21 F 2 plants showed different reaction following the inoculation with Xcc between the adaxial and abaxial leaf surface.On 10 plants,typical canker symptoms appeared on the adaxial leaf surface but not on the abaxial one;while for the other 11 plants,the typical symptoms inversely emerged on the abaxial leaf surface and not on the adaxial leaf surface.The quantification results of Xcc on the inoculated leaves was consistent with the of in vivo identification.In summary,no segregation of resistance and susceptibility was observed in F 1 progeny,but did in the F 2 generation.The ratio of resistant to susceptible F 2 plant was 1︰15,indicating that resistance and susceptibility may be inherited as quantitative traits.

Transcription factor CsbHLH3 plays an important role in regulating citrate metabolism in citrus fruits， but the specific mechanism remains unclear. In this study， the CsbHLH3 gene was cloned， and transient transformation in tobacco leaves demonstrated the subcellular localization of CsbHLH3 protein in the nucleus. CsbHLH3 overexpression tomato fruit showed a significant increase in the expression of CsbHLH3 while a significant decrease in the content of citrate relative to the wide type. Quantitative analysis revealed that the overexpression of CsbHLH3 induced the up-regulation of SlACO3b and SlPH8. On the contrary，transient suppression of the CsbHLH3 gene in Bingtangcheng leaves resulted in a significantly higher content of citrate than that of the control. In addition，the suppression of CsbHLH3 expression down-regulated the expression of the CsACO2，CsACLα1，CsACLα2 and CsGABP genes in the citrate degradation pathway and proton pump genes CsPH8，CsVHP2 and CsVHP3. Moreover，CsbHLH3 was further confirmed to target the promoter of PH8 and GABP genes to regulate their expression through Y1H and EMSA. These results suggest that the transcription factor CsbHLH3 negatively regulates the citrate level by regulating the expression of several genes related to citrate metabolism， including PH8 and the degradation gene GABP.

A stem-pitting isolate of citrus tristeza virus (CTV), spreading in Hunan province of China (HU-PSTS), was sequenced and indexed on indicator plants. Biological assays showed that HU-PSTS is a highly aggressive stem pitting isolate belonging to biogroup 5. Viral small RNAs (18-26 nt) of the isolate were deep sequenced by Illumina technology to gain genomic information on the CTV strain infecting the source plant. The reads mapping with 17 CTV reference genomes enabled us to re-assemble the genomes of VT, T68, T30 and T3 strains. Among the VT, the highest number of mapped reads (47-41%) was with SG29, T318A, CT11A, Nuaga and AT-1 genomes, whereas T68, T30 and T3 genomes were less represented (28-20%). Alignments with genomes belonging to T36 and RB strains revealed percentage of mapped reads ranging from 10 to 12%. This is the first sequenced genome of a CTV isolate from Hunan province. According to the results, further sequencing and bioindexing need to be developed to explore the potential of a local cross protective strategy.

\u3010Background\u3011<\/strong>Citrus canker is one of the serious citrus diseases caused by Xanthomonas citri<\/i> subsp. citri<\/i> (Xcc<\/i>). There is currently no radical cure method for it, and few of the existing cultivars have sufficient resistance to citrus canker. Therefore, the breeding for resistant varieties is crucial for the radical cure of the disease, and the identification of resistant genes is beneficial to disease-resistant cult

Promoting initiation and biomass production of roots is significant for plant-based industries including using roots as bioreactors. Two citrus genotypes, Carrizo and US-897, were used as model plants to test the effects of root-predominantly overexpressed the iaaM (indoleacetic acid-tryptophan monooxygenase) gene and a CKX (a cytokinin oxidase/dehydrogenase) gene. The iaaM transgenic lines exhibited markedly faster root initiation, more root numbers, and higher root biomass compared to their wild-type counterparts. The transgenic iaaM + CKX plants also exhibited similar phenotypes, albeit to a lesser extent than the iaaM plants. Molecular analysis revealed an auxin-responsive CsGH3.1 gene was up-regulated in the iaaM roots and iaaM + CKX roots, and a cytokinin-responsive gene CsARR5 gene was down-regulated in the iaaM + CKX roots. Our results demonstrate that root predominant overexpression of the iaaM or both the iaaM and CKX genes drastically enhances the initiation, growth and biomass production of roots. These results provide additional support that manipulation of auxin and cytokinin levels in roots via transgenic or gene-editing technologies may benefit production of high-value secondary metabolites using roots as bioreactors and also improve rooting of recalcitrant plant species.

BACKGROUND:Organic acids and anthocyanins are the most important compounds for the flavor and nutritional quality of citrus fruit. However, there are few reports on the involvement of co-regulation of citrate and anthocyanin metabolism. Here, we performed a comparative transcriptome analysis to elucidate the genes and pathways involved in both citrate and anthocyanin accumulation in postharvest citrus fruit with 'Tarocco' blood orange (TBO; high accumulation) and 'Bingtangcheng' sweet orange (BTSO; low accumulation).RESULTS:A robust core set of 825 DEGs were found to be temporally associated with citrate and anthocyanin accumulation throughout the storage period through transcriptome analysis. Further according to the results of weighted gene coexpression correlation network analysis (WGCNA), the turquoise and brown module was highly positively correlated with both of the content of citrate and anthocyanin, and p-type ATPase (PH8), phosphoenolpyruvate carboxylase kinase (PEPCK), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H) and glutathione S transferase (GST) were considered key structural genes. Moreover, MYB family transcription factor (PH4), Zinc finger PHD-type transcription factor (CHR4, HAC12), Zinc finger SWIM-type transcription factor (FAR1) and Zinc finger C3H1-type transcription factor (ATC3H64) were considered hub genes related to these structural genes. Further qRT-PCR analysis verified that these transcription factors were highly expressed in TBO fruit and their expression profiles were significantly positively correlated with the structural genes of citrate and anthocyanin metabolism as well as the content of citrate and anthocyanin content.CONCLUSIONS:The findings suggest that the CHR4, FAR1, ATC3H64 and HAC12 may be the new transcription regulators participate in controlling the level of citrate and anthocyanin in postharvest TBO fruit in addition to PH4. These results may providing new insight into the regulation mechanism of citrate and anthocyanin accumulation in citrus fruit.

Urban community gardens (UCGs), greenspace cultivated and managed for vegetables by local communities, provide substantial ecosystem services (ES) and are warmly welcomed by residents. However, they also have many ecosystem disservices (EDS) and are almost always refused by the decision-makers of the government, especially in China. Better understanding the residents’ perceived ES and EDS and the impact on the behavioral intention (BI) toward UCGs is of great value to solve the conflicts between residents and the government concerning UCGs and to develop sustainable UCGs. Following the theory of planned behavior (TPB), we measured perceived ES/EDS, attitudes (ATT), perceived behavioral control (PBC), subjective norm (SN), and BI of 1142 residents in Changsha, China, and investigated their direct and indirect causal relationships using structural equation modeling (SEM). The results showed that: (1) ATT, PBC, and SN significantly and positively impact the BI of UCGs and together explained 54% of the variation of BI. (2) The extended TPB model with additional components of perceived ED/EDS improved the explanatory ability of the model, explaining 65% of the variance of BI. Perceived ES and perceived EDS showed significant direct positive and negative impacts on UCGs, respectively. They also indirectly impacted BI by influencing ATT, PBC, and SN. The findings of this study can extend our understanding of residents’ attitudes, behavior, and driving mechanism toward UCGs, and can help decision makers to design better policies for UCG planning and management.