Biocontrol mechanism of Bacillus siamensis sp. QN2MO-1 against tomato fusarium wilt disease during fruit postharvest and planting.

Tomato fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici (Fol) is a highly destructive disease, resulting in severe economic losses of global tomato production annually. An eco-friendly alternative to chemical fungicide using biological control agents (BCAs) is urgently needed. Here, Bacillus siamensis QN2MO-1 was isolated from Noli fruit and had a strong antagonistic activity against Fol in vitro and in vivo. Strain QN2MO-1 also exhibited a broad-spectrum antifungal activity against the selected 14 phytopathogenic fungi. The crude protein produced by strain QN2MO-1 could inhibit the spore germination of Fol and destroy the spore structure. It was closely related with the generation of chitinase and ß-1,3-glucanase secreted by strain QN2MO-1. In a pot experiment, the application of B. siamensis QN2MO-1 effectively alleviated the yellowing and wilting symptoms of tomato plants. The disease index and incidence rate were decreased by 72.72% and 80.96%, respectively. The rhizospheric soil in tomato plants owed a high abundance of microbial community. Moreover, strain QN2MO-1 also enhanced the plant growth and improved the fruit quality of tomato. Therefore, B. siamensis QN2MO-1 will be explored as a potential biocontrol agent and biofertilizer.

A newly isolated Trichoderma Parareesei N4-3 exhibiting a biocontrol potential for banana fusarium wilt by Hyperparasitism.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race4 (Foc TR4) is one of the most destructive soil-borne fungal diseases and currently threatens banana production around the world. Until now, there is lack of an effective method to control banana Fusarium wilt. Therefore, it is urgent to find an effective and eco-friendly strategy against the fungal disease. In this study, a strain of Trichoderma sp. N4-3 was isolated newly from the rhizosphere soil of banana plants. The isolate was identified as Trichoderma parareesei through analysis of TEF1 and RPB2 genes as well as morphological characterization. In vitro antagonistic assay demonstrated that strain N4-3 had a broad-spectrum antifungal activity against ten selected phytopathogenic fungi. Especially, it demonstrated a strong antifungal activity against Foc TR4. The results of the dual culture assay indicated that strain N4-3 could grow rapidly during the pre-growth period, occupy the growth space, and secrete a series of cell wall-degrading enzymes upon interaction with Foc TR4. These enzymes contributed to the mycelial and spore destruction of the pathogenic fungus by hyperparasitism. Additionally, the sequenced genome proved that strain N4-3 contained 21 genes encoding chitinase and 26 genes encoding ß-1,3-glucanase. The electron microscopy results showed that theses cell wall-degrading enzymes disrupted the mycelial, spore, and cell ultrastructure of Foc TR4. A pot experiment revealed that addition of strain N4-3 significantly reduced the amount of Foc TR4 in the rhizosphere soil of bananas at 60 days post inoculation. The disease index was decreased by 45.00% and the fresh weight was increased by 63.74% in comparison to the control. Hence, Trichoderma parareesei N4-3 will be a promising biological control agents for the management of plant fungal diseases.

Genome-wide identification of PEBP gene family in pineapple reveal its potential functions in flowering.

Phosphatidylethanolamine binding protein (PEBP) plays an important role in regulating flowering time and morphogenesis of plants. However, the identification and functional analysis of PEBP gene in pineapple (AcPEBP) have not been systematically studied. The pineapple genome contained 11 PEBP family members, which were subsequently classified into three subfamilies (FT-like, TFL-like and MFT-like) based on phylogenetic relationships. The arrangement of these 11 shows an unequal pattern across the six chromosomes of pineapple the pineapple genome. The anticipated outcomes of the promoter cis-acting elements indicate that the PEBP gene is subject to regulation by diverse light signals and endogenous hormones such as ethylene. The findings from transcriptome examination and quantitative real-time polymerase chain reaction (qRT-PCR) indicate that FT-like members AcFT3 and AcFT4 display a heightened expression level, specifically within the floral structures. The expression of AcFT3 and AcFT4 increases sharply and remains at a high level after 4 days of ethylene induction, while the expression of AcFT7 and AcMFT1 decreases gradually during the flowering process. Additionally, AcFT3, AcFT4 and AcFT7 show specific expression in different floral organs of pineapple. These outcomes imply that members belonging to the FT-like subfamily may have a significant impact on the process of bud differentiation and flower development. Through transcriptional activation analysis, it was determined that AcFT4 possesses transcriptional activation capability and is situated in the nucleus and peripheral cytoplasm. Overexpression of AcFT4 in Arabidopsis resulted in the promotion of early flowering by 6-7 days. The protein interaction prediction network identified potential flower regulators, including CO, AP1, LFY and SOC1, that may interact with PEBP proteins. This study explores flower development in pineapple, thereby serving as a valuable reference for future research endeavors in this domain.

Transcriptome and Gene Co-Expression Network Analysis Identifying Differentially Expressed Genes and Signal Pathways Involved in the Height Development of Banana (Musa spp.).

Plant height is an important and valuable agronomic trait associated with yield and resistance to abiotic and biotic stresses. Dwarfism has positive effects on plant development and field management, especially for tall monocotyledon banana (Musa spp.). However, several key genes and their regulation mechanism of controlling plant height during banana development are unclear. In the present study, the popular cultivar 'Brazilian banana' ('BX') and its dwarf mutant ('RK') were selected to identify plant height-related genes by comparing the phenotypic and transcriptomic data. Banana seedlings with 3-4 leaves were planted in the greenhouse and field. We found that the third and fourth weeks are the key period of plant height development of the selected cultivars. A total of 4563 and 10507 differentially expressed genes (DEGs) were identified in the third and fourth weeks, respectively. Twenty modules were produced by the weighted gene co-expression network analysis (WGCNA). Eight modules were positively correlated with the plant height, and twelve other modules were negatively correlated. Combining with the analysis of DEGs and WGCNA, 13 genes in the signaling pathway of gibberellic acid (GA) and 7 genes in the signaling pathway of indole acetic acid (IAA) were identified. Hub genes related to plant height development were obtained in light of the significantly different expression levels (|log2FC| ≥ 1) at the critical stages. Moreover, GA3 treatment significantly induced the transcription expressions of the selected candidate genes, suggesting that GA signaling could play a key role in plant height development of banana. It provides an important gene resource for the regulation mechanism of banana plant development and assisted breeding of ideal plant architecture.

MYB30 and MYB14 form a repressor-activator module with WRKY8 that controls stilbene biosynthesis in grapevine.

When exposed to pathogen infection or ultraviolet (UV) radiation, grapevine (Vitis vinifera) plants rapidly accumulate the stilbenoid resveratrol (Res) with concomitant increase of stilbene synthase (STS), the key enzyme in stilbene biosynthesis. Although a few transcription factors have been shown to regulate STSs, the molecular mechanism governing the regulation of STSs is not well elucidated. Our previous work showed that a VvMYB14-VvWRKY8 regulatory loop fine-tunes stilbene biosynthesis in grapevine through protein-protein interaction; overexpression of VvWRKY8 down-regulates VvMYB14 and VvSTS15/21; and application of exogenous Res up-regulates WRKY8 expression. Here, we identified an R2R3-MYB repressor, VvMYB30, which competes with the activator VvMYB14 for binding to the common binding sites in the VvSTS15/21 promoter. Similar to VvMYB14, VvMYB30 physically interacts with VvWRKY8 through their N-termini, forming a complex that does not bind DNA. Exposure to UV-B/C stress induces VvMYB14, VvWRKY8, and VvSTS15/21, but represses VvMYB30 in grapevine leaves. In addition, MYB30 expression is up-regulated by VvWRKY8-overexpression or exogenous Res. These findings suggest that the VvMYB14-VvWRKY8-VvMYB30 regulatory circuit allows grapevine to respond to UV stress by producing Res and prevents over-accumulation of Res to balance metabolic costs. Our work highlights the stress-mediated induction and feedback inhibition of stilbene biosynthesis through a complex regulatory network involving multiple positive and negative transcriptional regulators.

Antifungal Mechanism of Metabolites from Newly Isolated Streptomyces sp. Y1-14 against Banana Fusarium Wilt Disease Using Metabolomics.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is one of the most destructive banana diseases in the world, which limits the development of the banana industry. Compared with traditional physical and chemical practices, biological control becomes a promising safe and efficient strategy. In this study, strain Y1-14 with strong antagonistic activity against Foc TR4 was isolated from the rhizosphere soil of a banana plantation, where no disease symptom was detected for more than ten years. The strain was identified as Streptomyces according to the morphological, physiological, and biochemical characteristics and the phylogenetic tree of 16S rRNA. Streptomyces sp. Y1-14 also showed a broad-spectrum antifungal activity against the selected 12 plant pathogenic fungi. Its extracts inhibited the growth and spore germination of Foc TR4 by destroying the integrity of the cell membrane and the ultrastructure of mycelia. Twenty-three compounds were identified by gas chromatography-mass spectrometry (GC-MS). The antifungal mechanism was investigated further by metabolomic analysis. Strain Y1-14 extracts significantly affect the carbohydrate metabolism pathway of Foc TR4 by disrupting energy metabolism.

AcBBX5, a B-box transcription factor from pineapple, regulates flowering time and floral organ development in plants.

Flowering is an important factor to ensure the success of plant reproduction, and reasonable flowering time is crucial to the crop yield. BBX transcription factors can regulate several growth and development processes. However, there is little research on whether BBX is involved in flower formation and floral organ development of pineapple. In this study, AcBBX5, a BBX family gene with two conserved B-box domains, was identified from pineapple. Subcellular localization analysis showed that AcBBX5 was located in the nucleus. Transactivation analysis indicated that AcBBX5 had no significant toxic effects on the yeast system and presented transcriptional activation activity in yeast. Overexpression of AcBBX5 delayed flowering time and enlarged flower morphology in Arabidopsis. Meanwhile, the expression levels of AtFT, AtSOC1, AtFUL and AtSEP3 were decreased, and the transcription levels of AtFLC and AtSVP were increased in AcBBX5-overexpressing Arabidopsis, which might lead to delayed flowering of transgenic plants. Furthermore, transcriptome data and QRT-PCR results showed that AcBBX5 was expressed in all floral organs, with the high expression levels in stamens, ovaries and petals. Yeast one-hybrid and dual luciferase assay results showed that AcBBX5 bound to AcFT promoter and inhibited AcFT gene expression. In conclusion, AcBBX5 was involved in flower bud differentiation and floral organ development, which provides an important reference for studying the functions of BBX and the molecular regulation of flower.

Genome-wide analysis of MADS-box families and their expressions in flower organs development of pineapple (Ananas comosus (L.) Merr.).

MADS-box genes play crucial roles in plant vegetative and reproductive growth, better development of inflorescences, flower, and fruit. Pineapple is a typical collective fruit, and a comprehensive analysis of the MADS-box gene family in the development of floral organs of pineapple is still lacking. In this study, the whole-genome survey and expression profiling of the MADS-box family in pineapple were introduced. Forty-four AcMADS genes were identified in pineapple, 39 of them were located on 18 chromosomes and five genes were distributed in five scaffolds. Twenty-two AcMADS genes were defined as 15 pairs of segmental duplication events. Most members of the type II subfamily of AcMADS genes had higher expression levels in floral organs compared with type I subfamily, thereby suggesting that AcMADS of type II may play more crucial roles in the development of floral organs of pineapple. Six AcMADS genes have significant tissue-specificity expression, thereby suggesting that they may participate in the formation of one or more floral organs. This study provides valuable insights into the role of MADS-box gene family in the floral organ development of pineapple.

Discovery of Niphimycin C from Streptomyces yongxingensis sp. nov. as a Promising Agrochemical Fungicide for Controlling Banana Fusarium Wilt by Destroying the Mitochondrial Structure and Function.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is the most destructive soil-borne fungal disease. Tropical race 4 (Foc TR4), one of the strains of Foc, can infect many commercial cultivars, which represents a threat to global banana production. Currently, there are hardly any effective chemical fungicides to control the disease. To search for natural product-based fungicides for controlling banana Fusarium wilt, we identified a novel strain Streptomyces yongxingensis sp. nov. (JCM 34965) from a marine soft coral, from which a bioactive compound, niphimycin C, was isolated using an activity-guided method. Niphimycin C exhibited a strong antifungal activity against Foc TR4 with a value of 1.20 µg/mL for EC50 and obviously inhibited the mycelial growth and spore germination of Foc TR4. It caused the functional loss of mitochondria and the disorder of metabolism of Foc TR4 cells. Further study showed that niphimycin C reduced key enzyme activities of the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC). It displayed broad-spectrum antifungal activities against the selected 12 phytopathogenic fungi. In pot experiments, niphimycin C reduced the disease indexes in banana plantlets and inhibited the infection of Foc TR4 in roots. Hence, niphimycin C could be a promising agrochemical fungicide for the management of fungal diseases.

The genome of Prunus humilis provides new insights to drought adaption and population diversity.

Prunus humilis (2n = 2x = 16) is a dwarf shrub fruit tree native to China and distributed widely in the cold and arid northern region. In this study, we obtained the whole genome sequences of P. humilis by combining Illumina, PacBio and HiC sequencing technologies. This genome was 254.38 Mb long and encodes 28,301 putative proteins. Phylogenetic analysis indicated that P. humilis shares the same ancestor with Prunus mume and Prunus armeniaca at ∼ 29.03 Mya. Gene expansion analysis implied that the expansion of WAX-related and LEA genes might be associated with high drought tolerance of P. humilis and LTR maybe one of the driver factors for the drought adaption by increase the copy number of LEAs. Population diversity analysis among 20 P. humilis accessions found that the genetic diversity of P. humilis populations was limited, only 1.40% base pairs were different with each other, and more wild resources need to be collected and utilized in the breeding and improvement. This study provides new insights to the drought adaption and population diversity of P. humilis that could be used as a potential model plant for horticultural research.

Genome-wide identification and characterization of the BBX gene family in pineapple reveals that candidate genes are involved in floral induction and flowering.

B-box zinc finger proteins contain one or two B-box domains, and sometimes, a CCT domain, which are involved in many biological processes, such as photomorphogenesis, flowering, anthocyanin synthesis and abiotic stress resistance. But the BBX gene family in pineapple has not been systematically studied. Nineteen BBX genes were detected in pineapple genome and divided into five groups according to phylogenetic analysis. The results of transcriptome analysis and RT-qPCR showed that most of AcBBX members were highly expressed during the flowering process, indicating that AcBBX gene may be involved in flower bud differentiation and morphogenesis. Transcriptional activation analysis showed that AcBBX6 and AcBBX18 had transcriptional activity and were located in the nucleus. Overexpression of AcBBX18 promoted flowering in Arabidopsis thaliana. These results provided a basis for further study functions and regulatory mechanism of BBX members in pineapple floral induction and flower development.

Biocontrol potential and antifungal mechanism of a novel Streptomyces sichuanensis against Fusarium oxysporum f. sp. cubense tropical race 4 in vitro and in vivo.

Most commercial banana cultivars are highly susceptible to Fusarium wilt caused by soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4). Biological control using antagonistic microorganism has been considered as an alternative method to fungicide. Our previous study showed that Streptomyces sp. SCA3-4 T had a broad-spectrum antifungal activity from the rhizosphere soil of Opuntia stricta in a dry hot valley. Here, the sequenced genome of strain SCA3-4 T contained 6614 predicted genes with 72.38% of G + C content. A polymorphic tree was constructed using the multilocus sequence analysis (MLSA) of five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). Strain SCA3-4 T formed a distinct clade with Streptomyces mobaraensis NBRC 13819 T with 71% of bootstrap. Average nucleotide identity (ANI) values between genomes of strain SCA3-4 T and S. mobaraensis NBRC 13819 T was 85.83% below 95-96% of the novel species threshold, and named after Streptomyces sichuanensis sp. nov. The type strain is SCA3-4 T (= GDMCC 4.214 T = JCM 34964 T). Genomic analysis revealed that strain SCA3-4 T contained 36 known biosynthetic gene clusters of secondary metabolites. Antifungal activity of strain SCA3-4 T was closely associated with the production of siderophore and its extracts induced the apoptosis of Foc TR4 cells. A total of 12 potential antifungal metabolites including terpenoids, esters, acid, macrolides etc. were obtained by the gas chromatography-mass spectrometry (GC-MS). Greenhouse experiment indicated that strain SCA3-4 T could significantly inhibit infection of Foc TR4 in the roots and corms of banana seedlings and reduce disease index. Therefore, strain SCA3-4 T is an important microbial resource for exploring novel natural compounds and developing biopesticides to manage Foc TR4. KEY POINTS: • Strain SCA3-4 T was identified as a novel species of Streptomyces. • Siderophore participates in the antifungal regulation. • Secondary metabolites of strain SCA3-4 T improves the plant resistance to Foc TR4.

Two divergent haplotypes from a highly heterozygous lychee genome suggest independent domestication events for early and late-maturing cultivars.

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.

Identification and Antifungal Mechanism of a Novel Actinobacterium Streptomyces huiliensis sp. nov. Against Fusarium oxysporum f. sp. cubense Tropical Race 4 of Banana.

Banana is an important fruit crop. Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) seriously threatens the global banana industry. It is difficult to control the disease spread using chemical measures. In addition, commercial resistant cultivars are also lacking. Biological control is considered as a promising strategy using antagonistic microbes. Actinomycetes, especially Streptomyces, are potential sources of producing novel bioactive secondary metabolites. Here, strain SCA2-4 T with strong antifungal activity against Foc TR4 was isolated from the rhizospheric soil of Opuntia stricta in a dry hot valley. The morphological, physiological and chemotaxonomic characteristics of the strain were consistent with the genus Streptomyces. Based on the homology alignment and phylogenetic trees of 16S rRNA gene, the taxonomic status of strain SCA2-4 T exhibited a paradoxical result and low bootstrap value using different algorithms in the MEGA software. It prompted us to further discriminate this strain from the closely related species by the multilocus sequence analysis (MLSA) using five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). The MLSA trees calculated by three algorithms demonstrated that strain SCA2-4 T formed a distinct clade with Streptomyces mobaraensis NBRC 13819 T . The MLSA distance was above 0.007 of the species cut-off. Average nucleotide identity (ANI) values between strain SCA2-4 T genome and two standard strain genomes were below 95-96% of the novel species threshold. Strain SCA2-4 T was assigned to a novel species of the genus Streptomyces and named as Streptomyces huiliensis sp. nov. The sequenced complete genome of SCA2-4 T encoded 51 putative biosynthetic gene clusters of secondary metabolites. Genome alignment revealed that ten gene clusters were involved in the biosynthesis of antimicrobial metabolites. It was supported that strain SCA2-4 T showed strong antifungal activities against the pathogens of banana fungal diseases. Extracts abstracted from the culture filtrate of strain SCA2-4 T seriously destroyed cell structure of Foc TR4 and inhibited mycelial growth and spore germination. These results implied that strain SCA2-4 T could be a promising candidate for biological control of banana Fusarium wilt.

Development of molecular markers based on the promoter difference of LcFT1 to discriminate easy- and difficult-flowering litchi germplasm resources and its application in crossbreeding.

BACKGROUND: Litchi is a well-known subtropical fruit crop. However, irregular bearing attributed to unstable flowering is a major ongoing problem for the development of the litchi industry. In a previous study, our laboratory proved that litchi flowering was induced by low temperature and that a FLOWERING LOCUS T (FT) homologue gene named LcFT1 played a pivotal role in this process. The present study aimed to understand the natural variation in FT among litchi germplasm resources and designed markers to verify easy- and difficult-flowering litchi germplasms. A grafting experiment was also carried out to explore whether it could shorten the seedling stage of litchi seedlings. RESULTS: Two types of LcFT1 promoter existed in different litchi germplasm resources, and we named them the 'easy-flowering type of LcFT1 promoter' and 'difficult-flowering type of LcFT1 promoter', which resulted in three different LcFT1 genotypes of litchi germplasm resources, including the homozygous easy-flowering type of the LcFT1 genotype, homozygous difficult-flowering type of the LcFT1 genotype and heterozygous LcFT1 genotype of litchi germplasm resources. The homozygous easy-flowering type of the LcFT1 genotype and heterozygous LcFT1 genotype of the litchi germplasm resources completed their floral induction more easily than the homozygous difficult-flowering type of the LcFT1 genotype of litchi germplasm resources. Herein, we designed two kinds of efficient molecular markers based on the difference in LcFT1 promoter sequences and applied them to identify of the easy- and difficult-flowering litchi germplasm resources. These two kinds of molecular markers were capable of clearly distinguishing the easy- from difficult-flowering litchi germplasm resources at the seedling stage and provided the same results. Meanwhile, grafting the scion of seedlings to the annual branches of adult litchi trees could significantly shorten the seedling stage. CONCLUSIONS: Understanding the flowering characteristics of litchi germplasm resources is essential for easy-flowering litchi breeding. In the present study, molecular markers provide a rapid and accurate approach for identifying the flowering characteristics. The application of these molecular markers not only significantly shortened the artificial crossbreeding cycle of easy-flowering litchi cultivars but also greatly saved manpower, material resources and land.

Chromosome-Scale Genome and Comparative Transcriptomic Analysis Reveal Transcriptional Regulators of ß-Carotene Biosynthesis in Mango.

Mango (2n = 2x = 40) is an important tropical/subtropical evergreen fruit tree grown worldwide and yields nutritionally rich and high-value fruits. Here, a high-quality mango genome (396 Mb, contig N50 = 1.03 Mb) was assembled using the cultivar "Irwin" from Florida, USA. A total of 97.19% of the sequences were anchored to 20 chromosomes, including 36,756 protein-coding genes. We compared the ß-carotene content, in two different cultivars ("Irwin" and "Baixiangya") and growth periods. The variation in ß-carotene content mainly affected fruit flesh color. Additionally, transcriptome analysis identified genes related to ß-carotene biosynthesis. MiPSY1 was proved to be a key gene regulating ß-carotene biosynthesis. Weighted gene co-expression network analysis, dual luciferase, and yeast one-hybrid assays confirmed that transcription factors (TFs) MibZIP66 and MibHLH45 activate MiPSY1 transcription by directly binding to the CACGTG motif of the MiPSY1 promoter. However, the two TFs showed no significant synergistic effect on promoter activity. The results of the current study provide a genomic platform for studying the molecular basis of the flesh color of mango fruit.

Integrative Analysis of the Coloring Mechanism of Red Longan Pericarp through Metabolome and Transcriptome Analyses.

The pericarp of longan (Dimocarpus longan Lour.) is rich in secondary metabolites and typically yellow-brown or gray-yellow in appearance. Here, we obtained a specific longan type, called red pericarp (RP) longan, which has a strong red pericarp. To understand the coloring mechanism of RP longan, metabolome and transcriptome data were used to analyze its secondary metabolites and molecular mechanism. From the results of liquid chromatography tandem mass spectrometry, 597 substances were identified in RP longan and 'Shixia' (SX) longan. Among these substances, 33 (mostly including flavonoids) were found in RP longan and 23 (mostly containing phenolic acids) were identified in SX longan. We identified five types of anthocyanins in longan pericarp, including three cyanidin derivatives, one delphinidin derivative, and one pelargonidin derivative. Three cyanidin derivatives, which contained cyanidin 3-O-glucoside, cyanidin 3-O-6″-malonyl-glucoside, and cyanidin O-syringic acid, were the primary components of anthocyanidins, and they only existed in RP longan. Delphinin 3-O-glucoside existed only in SX longan, and pelargonin O-rutinoside existed in RP and SX longan. However, their contents were extremely low. The structural genes F3H, F3'H, UFGT, and GST and the controlling genes containing MYB, bHLH, NAC, and MADS in the biosynthetic pathway of anthocyanin were significantly upregulated in RP longan. In summary, the strong red hue of RP longan is due to the accumulation of cyanidin derivatives in its pericarp, and the genes F3'H and F3'5'H may play an important role in selecting which component of anthocyanins will be synthesized. These results can provide scientific guidance for understanding and developing bioactive compounds from longan fruits.

Newly Isolated Streptomyces sp. JBS5-6 as a Potential Biocontrol Agent to Control Banana Fusarium Wilt: Genome Sequencing and Secondary Metabolite Cluster Profiles.

Banana is a key staple food and fruit in countries all over the world. However, the development of the global banana industry is seriously threatened by Fusarium wilt disease, which is caused by Fusarium oxysporum f. sp. cubense (Foc). In particular, Foc tropical race 4 (Foc TR4) could infect more than 80% of global banana and plantain crops. Until now, there were no commercial chemicals or resistant cultivars available to control the disease. Biological control using actinomycetes is considered a promising strategy. In this study, 88 actinomycetes were isolated from a banana orchard without symptoms of Fusarium wilt disease for more than 10 years. An actinobacterial strain labeled as JBS5-6 has exhibited strong antifungal activities against Foc TR4 and other selected 10 phytopathogenic fungi. Based on phenotypic and biochemical traits as well as complete genome analysis, strain JBS5-6 was assigned to Streptomyces violaceusniger. Extracts of the strain inhibited the mycelial growth and spore germination of Foc TR4 by destroying membrane integrity and the ultrastructure of cells. The complete genome of strain JBS5-6 was sequenced and revealed a number of key function gene clusters that contribute to the biosynthesis of active secondary metabolites. Sixteen chemical compounds were further identified by gas chromatography-mass spectrometry (GC-MS). 5-hydroxymethyl-2-furancarboxaldehyde was one of the dominant components in strain JBS5-6 extracts. Moreover, fermentation broth of strain JBS5-6 significantly reduced the disease index of banana seedlings by inhibiting the infection of Foc TR4 in a pot experiment. Hence, strain JBS5-6 is a potential biocontrol agent for the management of disease and the exploitation of biofertilizer.

Molecular and functional characterization of two DELLA protein-coding genes in litchi.

DELLA proteins are members of the plant-specific GRAS family, acting as negative regulators of plant growth. In this study, we identified two DELLA protein-coding genes in litchi, denoted as LcGAI and LcRGL1. Motif analysis showed that LcGAI and LcRGL1 proteins both contain a conserved DELLA and TVHYNP motif at the N-terminus as well as LHR1, VHIID, LHR2, PFYRE, and SAW motifs at the C terminus. The fused proteins of LcGAI-GFP and LcRGL1-GFP were both localized in the nucleus. Overexpression of LcGAI and LcRGL1 in Arabidopsis substantially inhibits leaf growth. Expression analysis showed that HLH factors, PRE1 and PRE5, were restrained, whereas gibberellin (GA) receptors GID1a and LcGID1b were enhanced in LcGAI and LcRGL1 overexpression lines. Results of the yeast two-hybrid assay showed that LcGAI and LcRGL1 interact with LcGID1b/LcGID1c in a GA dose-dependent manner, whereas LcGAI and LcRGL1 had a greater binding capacity to LcGID1b than LcGID1c. These observations suggested that LcGAI and LcRGL1 proteins are nuclear growth repressors.

VvWRKY8 represses stilbene synthase genes through direct interaction with VvMYB14 to control resveratrol biosynthesis in grapevine.

Resveratrol (Res) is a stilbenoid, a group of plant phenolic metabolites derived from stilbene that possess activities against pests, pathogens, and abiotic stresses. Only a few species, including grapevine (Vitis), synthesize and accumulate Res. Although stilbene synthases (STSs) have been isolated and characterized in several species, the gene regulatory mechanisms underlying stilbene biosynthesis are still largely unknown. Here, we characterize a grapevine WRKY transcription factor, VvWRKY8, that regulates the Res biosynthetic pathway. Transient and stable overexpression of VvWRKY8 in grapevine results in decreased expression of VvSTS15/21 and VvMYB14, as well as in a reduction of Res accumulation. VvWRKY8 does not bind to or activate the promoters of VvMYB14 and VvSTS15/21; however, it physically interacts with VvMYB14 proteins through their N-terminal domains to prevent them from binding to the VvSTS15/21 promoter. Application of exogenous Res results in the stimulation of VvWRKY8 expression and in a decrease of VvMYB14 and VvSTS15/21 expression in grapevine suspension cells, and in the activation of the VvWRKY8 promoter in tobacco leaves. These results demonstrate that VvWRKY8 represses VvSTS15/21 expression and Res biosynthesis through interaction with VvMYB14. In this context, the VvMYB14-VvSTS15/21-Res-VvWRKY8 regulatory loop may be an important mechanism for the fine-tuning of Res biosynthesis in grapevine.