Integrative Analysis of Metabolome and Transcriptome Provides Insights into the Mechanism of Flower Induction in Pineapple (Ananas comosus (L.) Merr.) by Ethephon.

Exogenous ethylene is commonly utilized to initiate flower induction in pineapple (Ananas comosus (L.) Merr.). However, the molecular mechanisms and metabolic changes involved are not well understood. In this study, we explored the genetic network and metabolic shifts in the 'Comte de Paris' pineapple variety during ethylene-induced flowering. This was achieved through an integrative analysis of metabolome and transcriptome profiles at vegetative shoot apexes (0 d after ethephon treatment named BL_0d), the stage of bract primordia (8 d after ethephon treatment named BL_8d), stage of flower primordia (18 d after ethephon treatment named BL_18d), and the stage of stopped floret differentiation (34 d after ethephon treatment named BL_34d). We isolated and identified 804 metabolites in the pineapple shoot apex and inflorescence, categorized into 24 classes. Notably, 29, 31, and 46 metabolites showed significant changes from BL_0d to BL_8d, BL_8d to BL_18d, and BL_18d to BL_34d, respectively. A marked decrease in indole was observed, suggesting its role as a characteristic metabolite during flower induction. Transcriptomic analysis revealed 956, 1768, and 4483 differentially expressed genes (DEGs) for BL_0d vs. BL_8d, BL_8d vs. BL_18d, and BL_18d vs. BL_34d, respectively. These DEGs were significantly enriched in carbohydrate metabolism and hormone signaling pathways, indicating their potential involvement in flower induction. Integrating metabolomic and transcriptomic data, we identified several candidate genes, such as Agamous-Like9 (AGL9), Ethylene Insensitive 3-like (ETIL3), Apetala2 (AP2), AP2-like ethylene-responsive transcription factor ANT (ANT), and Sucrose synthase 2 (SS2), that play potentially crucial roles in ethylene-induced flower induction in pineapple. We also established a regulatory network for pineapple flower induction, correlating metabolites and DEGs, based on the Arabidopsis thaliana pathway as a reference. Overall, our findings offer a deeper understanding of the metabolomic and molecular mechanisms driving pineapple flowering.

Transcriptome and metabolome response of eggplant against Ralstonia solanacearum infection.

Bacterial wilt is a soil-borne disease that represents ubiquitous threat to Solanaceae crops. The whole-root transcriptomes and metabolomes of bacterial wilt-resistant eggplant were studied to understand the response of eggplant to bacterial wilt. A total of 2,896 differentially expressed genes and 63 differences in metabolites were identified after inoculation with Ralstonia solanacearum. Further analysis showed that the biosynthesis pathways for phytohormones, phenylpropanoids, and flavonoids were altered in eggplant after inoculation with R. solanacearum. The results of metabolomes also showed that phytohormones played a key role in eggplant response to bacterial wilt. Integrated analyses of the transcriptomic and metabolic datasets indicated that jasmonic acid (JA) content and gene involved in the JA signaling pathway increased in response to bacterial wilt. These findings remarkably improve our understanding of the mechanisms of induced defense response in eggplant and will provide insights intothe development of disease-resistant varieties of eggplant.

Genome-Wide Identification and Expression Patterns of AcSWEET Family in Pineapple and AcSWEET11 Mediated Sugar Accumulation.

Pineapple (Ananas comosus L.) is an important fruit crop in tropical regions, and it requires efficient sugar allocation during fruit development. Sugars Will Eventually be Exported Transporters (SWEETs) are a group of novel sugar transporters which play critical roles in seed and fruit development. However, the function of AcSWEETs remains unknown in the sugar accumulation. Herein, 17 AcSWEETs were isolated and unevenly located in 11 chromosomes. Analysis of a phylogenetic tree indicated that 17 genes were classified into four clades, and the majority of AcSWEETs in each clade shared similar conserved motifs and gene structures. Tissue-specific gene expression showed that expression profiles of AcSWEETs displayed differences in different tissues and five AcSWEETs were strongly expressed during fruit development. AcSWEET11 was highly expressed in the stage of mature fruits in 'Tainong16' and 'Comte de paris', which indicates that AcSWEET11 was important to fruit development. Subcellular localization analysis showed that AcSWEET11 was located in the cell membrane. Notably, overexpression of AcSWEET11 could improve sugar accumulation in pineapple callus and transgenic tomato, which suggests that AcSWEET11 might positively contribute to sugar accumulation in pineapple fruit development. These results may provide insights to enhance sugar accumulation in fruit, thus improving pineapple quality in the future.

Genome-Wide Identification of Binding Sites for SmTCP7a Transcription Factors of Eggplant during Bacterial Wilt Resistance by ChIP-Seq.

Teosinte branched 1/cycloidea/proliferating cell factor (TCP) transcription factors play a key role in the regulation of plant biotic and abiotic stresses. In this study, our results show that SmTCP7a positively regulated bacterial wilt that was caused by Ralstonia solanacearum. ChIP-seq was conducted to analyze the transcriptional regulation mechanism of SmTCP7a before (R0 h) and 48 h after infection (R48 h). SmTCP7a regulated a total of 92 and 91 peak-associated genes in R0 h and R48 h, respectively. A KEGG (Kyoto encyclopedia of genes and genomes) pathway analysis showed that phenylpropanoid biosynthesis, MAPK (mitogen-activated protein kinas) signaling pathway, plant hormone signal transduction and plant-pathogen interactions were involved. The difference in peaks between R0 h and R48 h showed that there were three peak-associated genes that were modulated by infection. A better understanding of the potential target genes of SmTCP7a in response to R. solanacearum will provide a comprehensive understanding of the SmTCP7a regulatory mechanism during the eggplant defense response to bacterial wilt.

The highly continuous reference genome of a leaf-chimeric red pineapple (Ananas comosus var. bracteatus f. tricolor) provides insights into elaboration of leaf color.

Ananas comosus var. bracteatus f. tricolor (GL1) is a red pineapple accession whose mostly green leaves with chimeric white leaf margins turn red in spring and autumn and during flowering. It is an important ornamental plant and ideal plant research model for anthocyanin metabolism, chimeric leaf development, and photosynthesis. Here, we generated a highly contiguous chromosome-scale genome assembly for GL1 and compared it with other 3 published pineapple assemblies (var. comosus accessions MD2 and F153, and var. bracteatus accession CB5). The GL1 assembly has a total size of ∼461 Mb, with a contig N50 of ∼2.97 Mb and Benchmarking Universal Single-Copy Ortholog score of 97.3%. More than 99% of the contigs are anchored to 25 pseudochromosomes. Compared with the other 3 published pineapple assemblies, the GL1 assembly was confirmed to be more continuous. Our evolutionary analysis showed that the Bromeliaceae and Poaceae diverged from their nearest common ancestor ∼82.36 million years ago (MYA). Population structure analysis showed that while GL1 has not undergone admixture, bracteatus accession CB5 has resulted from admixture of 3 species of Ananas. Through classification of orthogroups, analysis of genes under positive selection, and analysis of presence/absence variants, we identified a series of genes related to anthocyanin metabolism and development of chimeric leaves. The structure and evolution of these genes were compared among the published pineapple assemblies with reveal candidate genes for these traits. The GL1 genome assembly and its comparisons with other 3 pineapple genome assemblies provide a valuable resource for the genetic improvement of pineapple and serve as a model for understanding the genomic basis of important traits in different pineapple varieties and other pan-cereal crops.

Genome-wide analysis of AP2/ERF transcription factors in pineapple reveals functional divergence during flowering induction mediated by ethylene and floral organ development.

The APETALA2/ethylene-responsive factor (AP2/ERF) has important roles in regulating developmental processes and hormone signaling transduction in plants. Pineapple demonstrates a special sensitivity to ethylene, and AP2/ERFs may contribute to this distinct sensitivity of pineapples to ethylene. However, little information is available on the AP2/ERF of pineapple. In this study, 97 AP2/ERF family members were identified from the pineapple genome. The AcAP2/ERF superfamily could be further divided into five subfamilies, and different subfamily existed functional divergence in multifarious biological processes. ERF and RAV subfamily genes might play important roles in the process of ethylene response of pineapple; ERF and DREB subfamily genes had particular functions in the floral organ development. This study is the first to provide detailed information on the features of AP2/ERFs in pineapple, provide new insights into the potential functional roles of the AP2/ERF superfamily members, and will facilitate a better understanding of the molecular mechanism of flower in pineapple.

Whole-Genome Bisulfite Sequencing Reveals a Role for DNA Methylation in Variants from Callus Culture of Pineapple (Ananas comosus L.).

DNA methylation changes can occur in some loci during callus culture, resulting in somaclonal variations (SVs). In the present study, we applied whole genome bisulfite sequencing to analyze context-specific DNA methylation changes in the pineapple genome between the cutting seedings and 5 SV plants. In general, SV plants exhibited methylation patterns analogous to those of cutting seedlings (CK). A total of 27.98% of the genomic cytosines of CK were methylcytosines, which was higher than that of 5 SV plants. Moreover, mCG and mCHG was hypermethylated, whereas mCHH was hypomethylated among the 5 SV plants genomic when compared with the CK. Most of the variation of DNA methylation was distributed in gene bodies, thus suggesting that phenotypic differences are probably perturbed by genes methylated from callus culture. In addition, the methylated genes were highly enriched for the Gene Ontology (GO) categories of binding and catalytic activity, cell part and organelle, cellular process, abiotic stimulus, and DNA modification. These results suggest that methylation mediates these pathways in the callus culture of pineapple. The results also suggested that the callus culture induced DNA methylation may result in the SV.

Identification of an Embryonic Cell-Specific Region within the Pineapple SERK1 Promoter.

Plant tissue culture methods, such as somatic embryogenesis, are attractive alternatives to traditional breeding methods for plant propagation. However, they often suffer from limited efficiency. Somatic embryogenesis receptor kinase (SERK)1 is a marker gene of early somatic embryogenesis in several plants, including pineapple. It can be selectively induced and promotes a key step in somatic embryogenesis. We investigated the embryonic cell-specific transcriptional regulation of AcSERK1 by constructing a series of vectors carrying the GUS（Beta-glucuronidase） reporter gene under the control of different candidate cis-regulatory sequences. These vectors were transfected into both embryonic and non-embryonic callus, and three immature embryo stages and the embryonic-specific activity of the promoter fragments was analyzed. We found that the activity of the regulatory sequence of AcSERK1 lacking -983 nt ~-880 nt, which included the transcription initiation site, was significantly reduced in the embryonic callus of pineapple, accompanied by the loss of embryonic cell-specific promoter activity. Thus, this fragment is an essential functional segment with highly specific promoter activity for embryonic cells, and it is active only from the early stages of somatic embryo development to the globular embryo stage. This study lays the foundation for identifying mechanisms that enhance the efficiency of somatic embryogenesis in pineapple and other plants.

Genome-Wide Analysis of Artificial Mutations Induced by Ethyl Methanesulfonate in the Eggplant (Solanum melongena L.).

Whole-genome sequences of four EMS (ethyl methanesulfonate)-induced eggplant mutants were analyzed to identify genome-wide mutations. In total, 173.01 GB of paired-end reads were obtained for four EMS-induced mutants and (WT) wild type and 1,076,010 SNPs (single nucleotide polymorphisms) and 183,421 indels were identified. The most common mutation type was C/G to T/A transitions followed by A/T to G/C transitions. The mean densities were one SNP per 1.3 to 2.6 Mb. The effect of mutations on gene function was annotated and only 7.2% were determined to be deleterious. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed 10 and 11 genes, which were nonsynonymous mutation or frameshift deletion in 48-5 and L6-5 involved in the anthocyanin biosynthesis or flavone and flavonol biosynthesis. QRT-PCR results showed that only the Sme2.5_06210.1_g00004.1, which was annotated as UFGT (Flavonoid galactosidase transferase), expression significantly decreased in the L6-5 mutant compared with the WT. Also, the Sme2.5_06210.1_g00004.1 expression was lower in the colorless eggplant compared with colorful eggplant in the natural eggplant cultivar. These results suggest that Sme2.5_06210.1_g00004.1 may play a key role in eggplant anthocyanin synthesis.

Effect of CPPU on Carbohydrate and Endogenous Hormone Levels in Young Macadamia Fruit.

N-(2-Chloro-4-pyridyl)-N'-phenylurea (CPPU) is a highly active cytokinin-like plant growth regulator that promotes chlorophyll biosynthesis, cell division, and cell expansion. It also increases fruit set and accelerates fruit enlargement. However, there has been no report about the effect of CPPU on fruit development and its physiological mechanism in macadamia. In this study, we investigated the effect of CPPU treatment at early fruit development via foliar spray or raceme soaking at 20 mg·L-1 on fruit set and related physiology in macadamia. Changes in carbohydrate contents and endogenous hormones in leaves, bearing shoots and fruit were also examined. Results showed that CPPU significantly reduced young fruit drop and delayed the wave of fruit drop by 1-2 weeks. The treatment significantly decreased the contents of total soluble sugars and starch in the leaves, but increased them in the bearing shoots and total soluble sugars in the husk (pericarp) and seeds. These findings suggested that CPPU promoted carbohydrate mobilization from the leaves to the fruit. In addition, CPPU increased the contents of indole-3-acetic acid (IAA), gibberellin acid (GA3), and zeatin riboside (ZR) and decreased the abscisic acid (ABA) in the husk. Therefore, CPPU treatment reduced the early fruit drop by increasing carbohydrate availability and by modifying the balance among endogenous hormones.