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.

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.

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.

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.

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.

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.

Transcriptome profiling of litchi leaves in response to low temperature reveals candidate regulatory genes and key metabolic events during floral induction.

BACKGROUND: Litchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas. Low temperature is absolutely required for floral induction of litchi, but its molecular mechanism is not fully understood. Leaves of litchi played a key role during floral induction and could be the site of low temperature perception. Therefore, leaves were treated under different temperature (15 °C/25 °C), and high-throughput RNA sequencing (RNA-Seq) performed with leaf samples for the de novo assembly and digital gene expression (DGE) profiling analyses to investigate low temperature-induced gene expression changes. RESULTS: 83,107 RNA-Seq unigenes were de novo assembled with a mean length of 1221 bp and approximately 61% of these unigenes (50,345) were annotated against public protein databases. Differentially-expressed genes (DEGs) under low temperature treatment in comparison with the control group were the main focus of our study. Hierarchical clustering analysis arranged 2755 DEGs into eight groups with three significant expression clusters (p-value ≤ 0.05) during floral induction. With the increasing contents of sugars and starch, the expression of genes involved in metabolism of sugars increased dramatically after low temperature induction. One FT gene (Unigene0025396, LcFT1) which produces a protein called 'florigen' was also detected among DEGs of litchi. LcFT1 exhibited an apparent specific tissue and its expression was highly increased after low temperature induction, GUS staining results also showed GUS activity driven by LcFT1 gene promoter can be induced by low temperature, which indicated LcFT1 probably played a pivotal role in the floral induction of litchi under low temperature. CONCLUSIONS: Our study provides a global survey of transcriptomes to better understand the molecular mechanisms underlying changes of leaves in response to low temperature induction in litchi. The analyses of transcriptome profiles and physiological indicators will help us study the complicated metabolism of floral induction in the subtropic evergreen plants.

A rapid and effective method for silver staining of PCR products separated in polyacrylamide gels.

With the development of molecular quantitative genetics, particularly, genetic linkage map construction, quantitative trait loci mapping or genes fine mapping and association analysis etc., more and more PCR products separated in polyacrylamide gels need to be silver-stained. However, conventional silver-staining procedures are complicated and time-consuming as they require a lot of preparation and handling of several solutions prior to use. In this study, a simple and rapid protocol for silver staining of PCR products was developed. The number of steps was reduced compared to conventional protocols, thus achieving detection of PCR products in 7 min, saving time and resources. Fixation and staining solution and developing solution in present staining procedure allowed a reutilization for 12 and 8 times, respectively, reducing the cost greatly. Meanwhile, the sensitivity was significantly improved with the improved method and the minimum of 0.097 ng/µL of DNA amount can be detected in denaturing polyacrylamide gel. The protocol developed in this study will facilitate the development of molecular quantitative genetics.

Transcriptomic analysis of floral initiation in litchi (Litchi chinensis Sonn.) based on de novo RNA sequencing.

KEY MESSAGE: Comparative transcriptome analysis of litchi ( Litchi chinensis Sonn.) buds at two developmental stages revealed multiple processes involving various phytohormones regulating floral initiation, and expression of numerous flowering-related genes. Floral initiation is a critical and complicated plant developmental process involving interactions of numerous endogenous and environmental factors, but little is known about the complex network regulating floral initiation in litchi (Litchi chinensis Sonn.). Illumina second-generation sequencing is an efficient method for obtaining massive transcriptional information resulting from phase changes in plant development. In this study, comparative transcriptomic analysis was performed with resting and emerging panicle stage buds, to gain further understanding of the molecular mechanisms involved in floral initiation in litchi. Abundance analysis identified 5,928 unigenes exhibiting at least twofold differences in expression between the two bud stages. Of these, 4,622 unigenes were up-regulated and 1,306 were down-regulated in panicle-emerging buds compared with resting buds. KEGG pathway enrichment analysis revealed that unigenes exhibiting differential expression were involved in the metabolism and signal transduction of various phytohormones. The expression levels of unigenes annotated as auxin, cytokinin, jasmonic acid, and salicylic acid biosynthesis were up-regulated, whereas those unigenes annotated as abscisic acid biosynthesis were down-regulated during floral initiation. In addition, 188 unigenes exhibiting sequence similarities to known flowering-related genes from other plants were differentially expressed during floral initiation. Thirteen genes were selected for confirmation of expression levels using quantitative-PCR. Our results provide abundant sequence resources for studying mechanisms underlying floral initiation in litchi and establish a platform for further studies of litchi and other evergreen fruit trees.

De novo assembly and characterization of pericarp transcriptome and identification of candidate genes mediating fruit cracking in Litchi chinensis Sonn.

Fruit cracking has long been a topic of great concern for growers and researchers of litchi (Litchi chinensis Sonn.). To understand the molecular mechanisms underlying fruit cracking, high-throughput RNA sequencing (RNA-Seq) was first used for de novo assembly and characterization of the transcriptome of cracking pericarp of litchi. Comparative transcriptomic analyses were performed on non-cracking and cracking fruits. A total of approximately 26 million and 29 million high quality reads were obtained from the two groups of samples, and were assembled into 46,641 unigenes with an average length of 993 bp. These unigenes can be useful resources for future molecular studies of the pericarp in litchi. Furthermore, four genes (LcAQP, 1; LcPIP, 1; LcNIP, 1; LcSIP, 1) involved in water transport, five genes (LcKS, 2; LcGA2ox, 2; LcGID1, 1) involved in GA metabolism, 21 genes (LcCYP707A, 2; LcGT, 9; Lcß-Glu, 6; LcPP2C, 2; LcABI1, 1; LcABI5, 1) involved in ABA metabolism, 13 genes (LcTPC, 1; Ca2+/H+ exchanger, 3; Ca2+-ATPase, 4; LcCDPK, 2; LcCBL, 3) involved in Ca transport and 24 genes (LcPG, 5; LcEG, 1; LcPE, 3; LcEXP, 5; Lcß-Gal, 9; LcXET, 1) involved in cell wall metabolism were identified as genes that are differentially expressed in cracked fruits compared to non-cracked fruits. Our results open new doors to further understand the molecular mechanisms behind fruit cracking in litchi and other fruits, especially Sapindaceae plants.

Taxonomic identification and antagonistic activity of Streptomyces luomodiensis sp. nov. against phytopathogenic fungi.

Banana wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is a devastating fungal disease. Biocontrol strategies hold immense potential for inhibiting the spread of Foc TR4. Here, 30 actinobacteria were isolated from soils and screened for their antagonistic activity against Foc TR4. Strain SCA4-21T was selected due to its strongest antagonistic activity against Foc TR4. Strain SCA4-21T also exhibited strong antagonistic activity against the other eight phytopathogenic fungi. The strain was identified as the genus Streptomyces according to its physiological, biochemical, and phenotypic characteristics. The phylogenetic trees of 16S rRNA sequences demonstrated that strain SCA4-21T formed a subclade with S. iranensis HM 35T and/or S. rapamycinicus NRRL B-5491T with low bootstrap values. Considering that 16S rRNAs did not provide sufficient resolution for species-level identification, the whole genome of strain SCA4-21T was sequenced. Multilocus sequence analysis (MLSA) based on five housekeeping gene alleles (atpD, gyrB, recA, rpoB, and trpB) revealed that strain SCA4-21T clustered into S. hygroscopicus subsp. hygroscopicus NBRC 13472T with 100% of bootstrap value. The analysis of the genome-based phylogeny also approved the results. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) were 91.26 and 44.30%, respectively, with values below the respective species level threshold of 95 and 70%. Hence, strain SCA 4-21T represented a novel species within the genus Streptomyces, named Streptomyces luomodiensis sp. nov. The type strain is SCA4-21T (=GDMCC4.340T = JCM36555T). By the CAZymes analysis, 348 carbohydrate-active enzymes (CAZymes) were detected, including 15 chitinases and eight ß-1,3-glucanases. The fermentation broth of strain SCA4-21T, exhibiting strong antagonistic activity against Foc TR4, demonstrated high activities of chitinase and ß-1,3-glucanase, which might be involved in antifungal activity. Our results showed an innovative potential biocontrol agent for managing plant fungal diseases, specifically banana fusarium wilt.

Streptomyces-Secreted Fluvirucin B6 as a Potential Bio-Fungicide for Managing Banana Fusarium Wilt and Mycotoxins and Modulating the Soil Microbial Community Structure.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc TR4) is the most destructive soil-borne fungal disease. Until now, there has been a lack of effective measures to control the disease. It is urgent to explore biocontrol agents to control Foc TR4 and the secretion of mycotoxin. In this study, fluvirucin B6 was screened from Streptomyces solisilvae using an activity-guided method. Fluvirucin B6 exhibited strong antifungal activity against Foc TR4 (0.084 mM of EC50 value) and significantly inhibited mycelial growth and spore germination. Further studies demonstrated that fluvirucin B6 could cause the functional loss of mitochondria, the disorder of metabolism of Foc TR4 cells, and the decrease of enzyme activities in the tricarboxylic acid cycle and electron transport chain, ultimately inhibiting mycotoxin metabolism. In a pot experiment, the application of fluvirucin B6 significantly decreased the incidence of banana Fusarium wilt and the amount of Foc TR4 and controlled fungal toxins in the soil. Additionally, fluvirucin B6 could positively regulate the changes in the structure of the banana rhizosphere microbial community, significantly enriching beneficial microbes associated with disease resistance. In summary, this study identifies fluvirucin B6, which plays versatile roles in managing fungal diseases and mycotoxins.

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.

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.

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.

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.

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.

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.