Fruit acidity, a key quality trait, is primarily determined by malic acid in many fruit crops. However, the molecular machinery governing its accumulation, particularly in response to hormonal cues like auxin, remains a "black box." Here, we systematically deconstruct the regulatory pathway controlling malic acid in litchi (Litchi chinensis). We first identify the tonoplast-localized transporter LcALMT1 as the principal channel for malate sequestration into the vacuole. We then uncover its upstream regulatory module, revealing that the R2R3-MYB transcription factor LcMYB70 directly binds the LcALMT1 promoter but lacks intrinsic transcriptional activity. Instead, LcMYB70 functions as a molecular scaffold to recruit the Auxin Response Factor LcARF10, which confers transcriptional repression upon the complex. This LcMYB70-LcARF10 repressor module is negatively regulated by auxin signaling, providing a direct molecular link between the decline in endogenous auxin during fruit maturation and the attenuation of malate accumulation. Critically, we identified a single-nucleotide polymorphism in the LcARF10 gene that governs the divergence between high- and low-acid cultivars. The functional C allele in low-acid cultivars enables the formation of the repressor complex. In contrast, the T allele in high-acid cultivars contains a premature stop codon that results in a non-functional, truncated protein, preventing complex assembly and causing the high-acid phenotype. Our study defines a complete pathway from hormone to trait and its genetic basis, revealing a novel MYB-ARF scaffold module; a definitive molecular link between auxin withdrawal and metabolic reprogramming; and the functional integrity of a corepressor as a new paradigm for trait diversification.

Longan (Dimocarpus longan Lour.) is highly sensitive to low temperature, which severely restricts its cultivation and industrial development. MYB transcription factors serve as key regulators in plant responses to cold stress. In this study, an R2R3-MYB gene DlMYB108 was cloned from ‘Shixia’ longan. Sequence analysis showed that DlMYB108 contains two typical MYB repeats and shares high homology with cold-responsive MYB108 proteins from other plants. Expression pattern analysis revealed that DlMYB108 is highly expressed in young leaves, which are more sensitive to cold stress, and is significantly induced by low-temperature treatment. Subcellular localization and transcriptional activation assays confirmed that DlMYB108 is a nuclear-localized transcriptional activator. Yeast one-hybrid and dual-luciferase assays demonstrated that DlMYB108 specifically binds to the promoters of DlCBF2 and DlCBF3 and activates their transcription. Heterologous expression of DlMYB108 in Arabidopsis significantly enhanced cold tolerance, accompanied by reduced ion leakage, malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation, as well as upregulated expression of CBF and cold-responsive genes. Collectively, DlMYB108 positively regulates longan cold tolerance through activating DlCBF2 and DlCBF3 expression, providing a valuable candidate gene for cold-tolerant longan breeding.

Dwarfism is a significant and desirable trait in the cultivation of horticultural crops. However, the regulatory mechanisms underlying dwarfism in perennial fruit trees remain poorly understood. In this study, we investigated the role of SRS genes in regulating plant height in Sapindaceae fruit trees, specifically litchi and longan. A total of five litchi SHORT INTERNODES (SHI)-related sequence genes (LcSRS) and four longan DlSRS genes were identified. Expression profile analysis in different tissues demonstrated that LcSRS1-LcSRS5 and DlSRS4 genes exhibited distinct expression patterns, with some genes showing tissue-specific expression. qRT-PCR analysis revealed that LcSRS5 and DlSRS4 genes had higher expression levels in the dwarf litchi ('Ziniangxi') and longan ('Shizi19') cultivars, respectively. Overexpression of the litchi LcSRS5 and the longan DlSRS4 in tobacco resulted in transgenic plants displaying a dwarf phenotype. Subcellular localization studies indicated that both LcSRS5 and DlSRS4 are localized in the nucleus of the cell. Hormone testing analysis indicated that the contents of auxin, cytokinin, and gibberellin varied among different cultivars of litchi and longan. GA3 treatment can promote the elongation of shoots in both litchi and longan. Additionally, silencing the LcSRS5 in litchi buds effectively promotes shoot growth, increases internode length, and significantly suppresses the expression of LcGA2ox1, LcGA2ox2, and LcGA2ox3 genes. Further studies confirmed that the LcSRS5 binds to the promoter of LcGA2ox3 to activate its expression. This study provides a foundation for further analysis of the functions of SRS genes in tropical fruit trees.

Litchi has great economic significance as a global fruit crop. However, the advancement of litchi functional genomics has encountered substantial obstacles due to its recalcitrance to stable transformation. Here, we present an efficacious Agrobacterium tumefaciens-mediated transformation system in somatic embryos of ‘Heiye’ litchi. This system was developed through the optimization of key variables encompassing explant selection, A. tumefaciens strain delineation, bacterium concentration, infection duration, and infection methodology. The subsequent validation of the transformation technique in litchi was realized through the ectopic expression of LcMYB1, resulting in the generation of transgenic calli. However, the differentiation of transgenic calli into somatic embryos encountered substantial challenges. To delineate the intricate molecular underpinnings of LcMYB1’s inhibitory role in somatic embryo induction, a comprehensive transcriptome analysis was conducted that encompassed embryogenic calli (C), globular embryos (G), and transgenic calli (TC). A total of 1,166 common differentially expressed genes (DEGs) were identified between C-vs.-G and C-vs.-TC. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that these common DEGs were mostly related to plant hormone signal transduction pathways. Furthermore, RT-qPCR corroborated the pronounced down-regulation of numerous genes that are associated with somatic embryo induction within the transgenic calli. The development of this transformation system provides valuable support for functional genomics research in litchi.

Litchi holds paramount economic significance as a global fruit crop. However, the advancement of litchi functional genomics encounters substantial obstacles due to its recalcitrance to stable transformation. Here, we present an efficacious A. tumefaciens-mediated transformation system in somatic embryo of ‘Heiye’ litchi. This system was developed through meticulous optimization of variables encompassing explant selection, A. tumefaciens strain delineation, bacterium concentration, infection duration, and infection methodology. The subsequent validation of the transformation technique in litchi was realized through the ectopic expression of LcMYB1, resulting in the generation of transgenic calli. However, it was discerned that the differentiation of transgenic calli into somatic embryos encountered substantial challenges. To delve into the intricate molecular underpinnings of LcMYB1’s inhibitory role in somatic embryo induction, a comprehensive transcriptome analysis was conducted encompassing embryogenic calli (C), globular embryos (G), and transgenic calli (TC). A total of 1166 common differentially expressed genes (DEGs) were identified between C-vs-G and C-vs-TC. Gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that these common DEGs were most related to plant hormone signal transduction pathways. Furthermore, RT-qPCR corroborated pronounced down-regulation of numerous genes intricately associated with somatic embryos induction within the transgenic calli. The development of this transformation system has provided valuable support for functional genomics research in litchi.

Lychee is an exotic tropical fruit with a distinct flavor. The genome of cultivar ‘Feizixiao’ was assembled into 15 pseudochromosomes, totaling ~470 Mb. High heterozygosity (2.27%) resulted in two complete haplotypic assemblies. A total of 13,517 allelic genes (42.4%) were differentially expressed in diverse tissues. Analyses of 72 resequenced lychee accessions revealed two independent domestication events. The extremely early maturing cultivars preferentially aligned to one haplotype were domesticated from a wild population in Yunnan, whereas the late-maturing cultivars that mapped mostly to the second haplotype were domesticated independently from a wild population in Hainan. Early maturing cultivars were probably developed in Guangdong via hybridization between extremely early maturing cultivar and late-maturing cultivar individuals. Variable deletions of a 3.7 kb region encompassed by a pair of CONSTANS -like genes probably regulate fruit maturation differences among lychee cultivars. These genomic resources provide insights into the natural history of lychee domestication and will accelerate the improvement of lychee and related crops.

Longan (Dimocarpus longan Lour.) is of great economic significance in South China for its unique taste and nutritional properties. However, longan breeding is mainly based on seedling selection, which generally results in small fruits, low flesh recovery, and few seedless germplasm. Triploid breeding is a central way to improve these problems. In this study, microspore chromosomes were doubled by colchicine and high-temperature treatment to create triploids in longans. The relationship between the development process of male gametophyte of longans and the morphological changes of male flower buds was established. Cytological observation showed that when the male flower buds were in stage I (when the diameter of the flower bud is 1.4–2.0 mm), most of the microspores were at the pachytene to diakinesis stage of meiosis, and the chromosome doubling induction effect was the best at this stage. The results showed that the 2n pollen rate induced by a high temperature of about 38 °C was higher than that induced by colchicine treatment. The highest 2n pollen rate was 5.7% and 5.5% based on the microscopic measurement method and the abnormal separation in tetrad stage estimation method, respectively. Four triploids were successfully obtained from artificial pollination with 2n pollen, with a triploid induction rate of 0.6%. This study will promote ploidy breeding in longan.

"脆丰龙眼"是以"大乌圆龙眼"为母本,"石硖龙眼"为父本的F1杂交后代,经过多年连续观察筛选出的早结丰产大果型龙眼新品种,2021年8月通过了广东省农作物品种评定委员会评定,评定编号为粤评果20210003."脆丰龙眼"果实较大,扁圆形,果皮黄褐色,果肉浅蜡黄,离核,肉质脆嫩化渣,清甜多汁,略有香气;平均单果重13.8g,平均果皮厚度为0.61mm,裂果率较低;可食率69.6％,可溶性固形物含量19.3％,总糖含量16.5g·100g-1,还原糖含量7.4g·100g-1,可滴定酸含量0.25g·kg-1,维生素C含量55.6mg·100g-1."脆丰龙眼"早结丰产,稳产性好,优质大果,在广州地区7月21—31日成熟,在潮汕地区8月1—20日成熟,适宜在龙眼产区推广种植.

华蜜黄皮是以白糖黄皮为母本、郁南无核黄皮为父本进行杂交,从杂交F1代群体中单株优选而成的黄皮新品种.果实鸡心形,果皮橙黄色;肉质细嫩,风味蜜甜,有香气;平均单果质量7.98 g,平均单果种子数1.1粒,可食率69.6％;可溶性固形物含量(w,后同)18.8％,总糖11.8％,还原糖5.4％,可滴定酸0.1％,维生素C602mg·kg-1.华蜜黄皮树势较旺,丰产稳产性较好,早熟,在广州6月底至7月上旬成熟,成熟度较一致,适宜在广东省黄皮产区推广种植.

Background Litchi chinensis Sonn. is an economically important fruit tree in tropical and subtropical regions. However, litchi functional genomics is severely hindered due to its recalcitrance to regeneration and stable transformation. Agrobacterium rhizogenes -mediated hairy root transgenic system provide an alternative to study functional genomics in woody plants. However, the hairy root transgenic system has not been established in litchi. Results In this study, we report a rapid and highly efficient A . rhizogenes -mediated co-transformation system in L. chinensis using Green Fluorescent Protein ( GFP ) gene as a marker. Both leaf discs and stem segments of L. chinensis cv. ‘Fenhongguiwei’ seedlings were able to induce transgenic hairy roots. The optimal procedure involved the use of stem segments as explants, infection by A . rhizogenes strain MSU440 at optical density (OD 600 ) of 0.7 for 10 min and co-cultivation for 3 days, with a co-transformation efficiency of 9.33%. Furthermore, the hairy root transgenic system was successfully used to validate the function of the key anthocyanin regulatory gene LcMYB1 in litchi. Over-expression of LcMYB1 produced red hairy roots, which accumulated higher contents of anthocyanins, proanthocyanins, and flavonols. Additionally, the genes involving in the flavonoid pathway were strongly activated in the red hairy roots. Conclusion We first established a rapid and efficient transformation system for the study of gene function in hairy roots of litchi using A . rhizogenes strain MSU440 by optimizing parameters. This hairy root transgenic system was effective for gene function analysis in litchi using the key anthocyanin regulator gene LcMYB1 as an example.

华蜜2号黄皮是以白糖黄皮为母本、郁南无核黄皮为父本进行杂交,从杂交F,代群体中单株优选而成的黄皮新品种.果实椭圆形,果皮黄褐色;肉质细嫩化渣,蜜甜微酸,香气浓郁;平均单果质量10.08 g,平均单果种子数1.92粒,可食率66.5％;可溶性固形物含量(w,后同)为17.8％,总糖含量11.1％,还原糖含量7.8％,总酸含量1.78％,维生素C含量516mg·kg-1.华蜜2号黄皮树势较旺,树姿开张,丰产稳产性较好,生产示范区平均产量22 500kg·hm-2.中熟,在广州地区7月上中旬成熟,成熟度较一致,适宜在广东省黄皮产区推广种植.

The pathogenic fungus Neoscytalidium dimidiatum (Nd) is the causal agent of pitaya canker and causes significant yield losses. The mechanism by which Nd invades pitaya stems remains largely unknown. Here, quantitative proteomic analysis was employed to investigate pitaya immune responses against Nd infection. A total of 2766 proteins including 244 differentially expressed proteins (DEPs) were identified during infection. Nearly half of the upregulated proteins were predicted to be located in the chloroplast and mitochondrion, implying that these organelles are most affected by fungal infection. Bioinformatics analysis indicated that the DEPs were associated with photosynthesis, phytohormone activity, reactive oxygen species (ROS) homeostasis, and pathogenic defense responses. Notably, the phytohormones auxin and abscisic acid were accumulated for defense against Nd invasion. qRT-PCR validation showed that the mRNA expression levels of auxin binding protein (ABP), auxin response 4 protein (ARP4), and aspartic protease 2 (ASP2) were not consistent with the protein variation, suggesting that these proteins were regulated post-transcriptionally. Additionally, DEPs associated with ROS metabolism changed markedly, indicating that ROS homeostasis in pitaya is important for defense against Nd invasion. In summary, the results revealed the involvement of many essential proteins in the response to Nd infection and provide a basis for studying other biotic stresses of pitaya.

Longan (Dimocarpus longan) is a typical southern subtropical fruit tree species that is sensitive to cold stress. C-repeat binding factors (CBFs), as transcription factors, are crucial components involved in the molecular regulation of the plant response to cold stress. However, the role of CBF homologs in the cold response regulation of longan remains largely unknown. Here, three novel CBF genes, DlCBF1, DlCBF2, and DlCBF3, were cloned from longan. DlCBF1 and DlCBF2 contain an AP2 domain and PKKPAGR and DSAWR CBF signature motifs, while DlCBF3 has mutations within these conserved signature motifs. DlCBF1/2/3 were mainly localized in the nucleus and specifically bound to CRT/DRE cis-elements, resulting in strong transcriptional activation. DlCBF1/2 exhibited tissue expression specificity, and their expression was induced by low temperature, while DlCBF3 had no tissue specificity and barely responded to low temperature. DlCBF1, DlCBF2, and DlCBF3 overexpression in Arabidopsis-enhanced cold tolerance by increasing proline accumulation and reducing reactive oxygen species (ROS) content, accompanied by upregulated expression of cold-responsive genes (AtRD29A, AtCOR15A, AtCOR47, and AtKIN1) in the CBF cold stress response signaling pathway. In conclusion, the biological functions of DlCBF1/2/3 were somewhat conserved, but slow expression of DlCBF1/2 and low expression of DlCBF3 may partly cause the cold sensitivity of longan. Collectively, these results indicated that differences exist in the expression and function of CBF orthologs in the cold-sensitive plant species longan, and these findings may help to improve the understanding of the cold response regulation mechanism and provide important theoretical support for cold-tolerant breeding of longan.

《园艺产品营养与功能》是华南农业大学园艺学院面向本学院学生开出的一门选修课.本文从开课目的与教学目标、教材选用、教学学时与内容、教学方法、考核方式等方面阐述课程体系构建.2020春季学期受新型冠状肺炎疫情影响,课程由原计划线下教学改为线上教学的方式,线上课程采用录播视频、钉钉平台直播、微信答疑等教学方式,取得了较好的效果,本文将总结一个学期课程构建及线上取得的教学经验.

BackgroundSWEETs (Sugar Will Eventually be Exported transporters) function as sugar efflux transporters that perform diverse physiological functions, including phloem loading, nectar secretion, seed filling, and pathogen nutrition. The SWEET gene family has been identified and characterized in a number of plant species, but little is known about in Litchi chinensis, which is an important evergreen fruit crop.ResultsIn this study, 16 LcSWEET genes were identified and nominated according to its homologous genes in Arabidopsis and grapevine. Multiple sequence alignment showed that the 7 alpha-helical transmembrane domains (7-TMs) were basically conserved in LcSWEETs. The LcSWEETs were divided into four clades (Clade I to Clade IV) by phylogenetic tree analysis. A total of 8 predicted motifs were detected in the litchi LcSWEET genes. The 16 LcSWEET genes were unevenly distributed in 9 chromosomes and there was one pairs of segmental duplicated events by synteny analysis. The expression patterns of the 16 LcSWEET genes showed higher expression levels in reproductive organs. The temporal and spatial expression patterns of LcSWEET2a and LcSWEET3b indicated they play central roles during early seed development.ConclusionsThe litchi genome contained 16 SWEET genes, and most of the genes were expressed in different tissues. Gene expression suggested that LcSWEETs played important roles in the growth and development of litchi fruits. Genes that regulate early seed development were preliminarily identified. This work provides a comprehensive understanding of the SWEET gene family in litchi, laying a strong foundation for further functional studies of LcSWEET genes and improvement of litchi fruits.

ICE1 (inducer of CBF expression 1) encodes a typical MYC-like basic helix-loop- helix (bHLH) transcription factor that acts as a pivotal component in the cold signalling pathway. In this study, DlICE1, a novel ICE1-like gene, was isolated from the southern subtropical fruit tree longan (Dimocarpus longan Lour.). DlICE1 encodes a nuclear protein with a highly conserved bHLH domain. DlICE1 expression was slightly upregulated under cold stress. Overexpression of DlICE1 in Arabidopsis conferred enhanced cold tolerance via increased proline content, decreased ion leakage, and reduced malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation. Expression of the ICE1-CBF cold signalling pathway genes, including AtCBF1/2/3 and cold-responsive genes (AtRD29A, AtCOR15A, AtCOR47 and AtKIN1), was also significantly higher in DlICE1-overexpressing lines than in wild-type (WT) plants under cold stress. In conclusion, these findings indicate that DlICE1 is a member of the bHLH gene family and positively regulates cold tolerance in D. longan.

Aiming to breed a new cultivar with late maturation and large fruit size, three F1 intergeneric hybrids of longan and litchi populations, viz. 'Shixia' x 'Ziniangxi', Z'aoshu' x 'Ziniangxi' and 'Zhongqiu' x 'Ziniangxi' were evaluated under this experiment. Using the progenies as materials, 30 fruit quality traits including harvesting date, fruit weight, flesh thickness, seed weight, edible: non-edible ratio, soluble solids content, flavor of fruit, etc. were assessed and evaluated. The results showed that there was a significant difference in fruit quality traits among different hybrid progenies. The individual selections were evaluated by the quality weighed average, which was calculated as the scores of three different traits including fruit weight, the edible/non-edible ratio and the soluble solids content. Four hybrids ('Shizi-2', 'Shizi-9', 'Shizi-19' and 'Zaozi-1') were identified as superior individuals with a quality weighed average of more than 83, showing late maturation, large fruit size with high edible/ non-edible ratio. Hence, these individuals will have great value in production application and breeding.

In this study, two F1 longan hybrid populations named FDD265 and FDD97 were created in 2012, using 'Daguocaopu' as pollen parent, meanwhile 'FD265' and 'FD97' selected from 'Fengliduo' x 'Dawuyuan' (FD) F1 population as maternal parents, respectively. In order to obtain reliable hybrids, we developed to identify the hybrids using paternal homozygosis dominant marker. Firstly, using the parental genomic DNA of FDD265 and FDD97 as templates, 88 and 90 of 274 pairs of SSR primers could amplify the paternal specific markers separately. Secondly, these paternal specific markers were used to screen the inseparable loci using the self-crossed progenies of pollen parent 'Daguocaopu'. Finally, 3 and 1 paternal homozygous dominant markers were selected for identifying 67 and 66 individuals of FDD265 and FDD97 populations, respectively. The result showed that all hybrids of the two populations were identified as real hybrids with the high rates up to 100% hybridity. This result indicates the accuracy and effectiveness of this method for identifying young hybrids using paternal homozygosis dominant marker.

Knowledge on the subcellular localization of target proteins in a plant mutant background is important for revealing the function of the genes investigated. However, in Arabidopsis and rice, mutant lethality is one major barrier to such studies. Here we describe an optimized bombardment-mediated transient expression approach for studying subcellular protein localization in Arabidopsis seedling of lethal mutants. The whole experiment comprises four stages: cultivation and preparation of plants, coating gold particles with plasmid DNA, delivery of DNA into plants via bombardment, plant incubation and gene expression analysis which include localization and dynamics, co-localization comparison with reporter proteins and functional analysis. The entire process takes about 3-10 days from plant cultivation to protein detection. It has a high efficiency and the results are reproducible. Additionally, this protocol is applicable for the transient expression of chimeric fluorescent fusion proteins in juvenile rice seedlings and leaf sheaths, saving time dramatically in comparison of generating transgenic rice plant.

In order to study the cold resistance of litchi and longan, 32 accessions including cultivars of litchi and longan, intraspecific hybrids of litchi and longan, and intergeneric hybrids between longan and litchi were selected as materials. In this study, the relative electric conductivity and the damage rate were calculated by measuring the electric conductivity of all accessions' leaves under different low temperature treatment. Then the lethal dose-50 temperature (LT50) was used as the main index to evaluate the cold resistance of all accessions and selected germ-plasm resources with strong cold resistance, this was calculated using the Logistic regression equation for the damage rate. The results showed that 'Fengduziyuan' longan has an excellent cold resistance with the lowest LT50 of -6.01 degrees C, followed by 'Fengliduo' longan with an LT50 of about -4.97 degrees C. The longan intraspecific hybrid 'FD 82' and intergeneric hybrid 'Shizi No. 26' were the most susceptible to cold with a LT50 of about 0.27 and -0.90 degrees C respectively. In addition, there was a wide separation in cold resistance among the ten intergeneric hybrids and their parents. 'Zaozi No. 1' and 'Shizi No. 19' had a stronger resistance to cold with a LT50 of about -4.41 degrees C, compared to 'Shizi No. 26' which had a weaker cold resistance. The results the superiority in creating a new germplasm resource with an excellent cold resistance can be reached through distant hybridization.