Integrated analysis of the metabolome and transcriptome provides insights into anthocyanin biosynthesis of cashew apple

The cashew apple remains an underutilized agricultural product despite its abundance as a by-product of cashew nut production. Anthocyanins are water-soluble pigments responsible for red, purple, and blue hues in plant tissues and have various health-promoting properties. To investigate the anthocyanin biosynthesis in cashew apples, fruits with varying peel colors from three cultivars were subjected to integrative analyses with metabolomics and transcriptomics. Through a UPLC-ESI-MS/MS-based targeted metabolomics analysis, a total of 26 distinct anthocyanin compounds were identified in the fruits of the three cashew cultivars. Subsequent quantification revealed that Pelargonidin-3-O-galactoside, Petunidin-3-O-arabinoside, and Cyanidin-3-O-galactoside were the primary contributors responsible for the red pigmentation in cashew apple peels. Following transcriptomic analysis showed that the expression levels of anthocyanin biosynthetic genes were predominantly higher in the red cashew apples as compared to the other two cultivars. Moreover, correlation analysis revealed that eight potential transcription factors implicated in the regulation of anthocyanin biosynthesis. Among these, four transcription factors exhibited positive correlations with both anthocyanin contents and anthocyanin biosynthetic gene expression, while the remaining four transcription factors displayed negative correlations. These findings provide a comprehensive understanding of the molecular basis of anthocyanin biosynthesis in cashew apple peels.

Transcriptome profiling of cashew apples (Anacardium occidentale) genotypes reveals specific genes linked to firmness and color during pseudofruit development

We found 34 and 71 key genes potentially involved in flavonoid biosynthesis and cell wall disassembly, respectively, which could be associated with specific peel coloration and softening of each genotype. Cashew apple (Anacardium occidentale) has a great economic importance worldwide due to its high nutritional value, peculiar flavor and aroma. During ripening, the peduncle develops different peel color and becomes quickly fragile due to its oversoftening, impacting its consumers' acceptance. In view of this, the understanding about its transcriptional dynamics throughout ripening is imperative. In this study, we performed a transcriptome sequencing of two cashew apple genotypes (CCP 76 and BRS 265), presenting different firmness and color peel, in the immature and ripe stages. Comparative transcriptome analysis between immature and ripe cashew apple revealed 4374 and 3266 differentially expressed genes (DEGs) to CCP 76 and BRS 265 genotypes, respectively. These genes included 71 and 34 GDEs involved in the cell wall disassembly and flavonoid biosynthesis, respectively, which could be associated with firmness loss and anthocyanin accumulation during cashew apple development. Then, softer peduncle of CCP 76 could be justified by down-regulated EXP and up-regulation of genes involved in pectin degradation (PG, PL and PAE) and in cell wall biosynthesis. Moreover, genes related to flavonoid biosynthesis (PAL, C4H and CHS) could be associated with early high accumulation of anthocyanin in red-peel peduncle of BRS 265. Finally, expression patterns of the selected genes were tested by real-time quantitative PCR (qRT-PCR), and the qRT-PCR results were consistent with transcriptome data. The information generated in this work will provide insights into transcriptome responses to cashew apple ripening and hence, it will be helpful for cashew breeding programs aimed at developing genotypes with improved quality traits.

Plastome Sequencing of Ten Nonmodel Crop Species Uncovers a Large Insertion of Mitochondrial DNA in Cashew

In plant evolution, intracellular gene transfer (IGT) is a prevalent, ongoing process. While nuclear and mitochondrial genomes are known to integrate foreign DNA via IGT and horizontal gene transfer (HGT), plastid genomes (plastomes) have resisted foreign DNA incorporation and only recently has IGT been uncovered in the plastomes of a few land plants. In this study, we completed plastome sequences for l0 crop species and describe a number of structural features including variation in gene and intron content, inversions, and expansion and contraction of the inverted repeat (IR). We identified a putative in cinnamon ( J. Presl) and other sequenced Lauraceae and an apparent functional transfer of to the nucleus of quinoa ( Willd.). In the orchard tree cashew ( L.), we report the insertion of an ∼6.7-kb fragment of mitochondrial DNA into the plastome IR. BLASTn analyses returned high identity hits to mitogenome sequences including an intact open reading frame. Using three plastome markers for five species of , we generated a phylogeny to investigate the distribution and timing of the insertion. Four species share the insertion, suggesting that this event occurred <20 million yr ago in a single clade in the genus. Our study extends the observation of mitochondrial to plastome IGT to include long-lived tree species. While previous studies have suggested possible mechanisms facilitating IGT to the plastome, more examples of this phenomenon, along with more complete mitogenome sequences, will be required before a common, or variable, mechanism can be elucidated.

Purification and Characterization of Anacardium occidentale (Cashew) Allergens Ana o 1, Ana o 2, and Ana o 3

In this study a fast and simple purification procedure for the three known allergens from cashew (7S globulin Ana o 1, 11S globulin Ana o 2, and 2S albumin Ana o 3) is described. The purified allergens are characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blot, glycoprotein stain, and protein identification. The purified proteins still bind IgE, and this IgE binding varied between different pools of patient serum. Ana o 1 was found to be a glycoprotein. Ana o 3 has been studied more in detail to identify both the small and large subunits, both displaying microheterogeneity, and epitope mapping of Ana o 3 has been performed.

Rapid screening for potential epitopes reactive with a polycolonal antibody by solution-phase H/D exchange monitored by FT-ICR mass spectrometry

The potential epitopes of a recombinant food allergen protein, cashew Ana o 2, reactive to polyclonal antibodies, were mapped by solution-phase amide backbone H/D exchange (HDX) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Ana o 2 polyclonal antibodies were purified in the serum from a goat immunized with cashew nut extract. Antibodies were incubated with recombinant Ana o 2 (rAna o 2) to form antigen:polyclonal antibody (Ag:pAb) complexes. Complexed and uncomplexed (free) rAna o 2 were then subjected to HDX-MS analysis. Four regions protected from H/D exchange upon pAb binding are identified as potential epitopes and mapped onto a homologous model.

Isolation, characterization, and determination of 1-O-trans-cinnamoyl-beta-D-glucopyranose in the epidermis and flesh of developing cashew apple (Anacardium occidentale L.) and four of its genotypes

1-O-trans-Cinnamoyl-beta-d-glucopyranose was purified from cashew apple (Anacardium occidentale L.) juice and unambiguously characterized. Absent at the immature green stage, its concentration bursts at the turning and even more at the mature ripe stage, reaching 6.2 mg/100 g of fresh weight. Whatever the considered cashew apple genotype, this cinnamoyl glucoside ester was preferentially concentrated in the epidermis, which was 4-5 times richer than flesh, reaching 85 mg/100 g of fresh weight for skin of the Brazilian clone EMBRAPA 50. Entire cashew apples contained from 6 to 20 mg of 1-cinnamoylglucose/100 g, a concentration similar to that of red strawberry receptacle. Accumulation of such amounts in this false fruit remains to be explained.

Ana o 3, an important cashew nut (Anacardium occidentale L.) allergen of the 2S albumin family

BACKGROUND

Cashew nut allergy is the second most commonly reported tree nut allergy in the United States. We have previously cloned and characterized major cashew allergens belonging to the vicilin and legumin families of seed storage proteins.

OBJECTIVE

Here we set out to describe a third major cashew allergen, a 2S albumin.

METHODS

The recombinant cashew 2S albumin was amplified from a cDNA library by means of PCR, sequenced, and expressed in Escherichia coli. Immunoblotting was used to screen for reactivity with patients' sera, and inhibition immunoblotting was used to identify the corresponding native cashew nut proteins. The mass of affinity-purified native allergen was determined by means of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectroscopy. Patients' sera were used to probe solid-phase 2S albumin peptides to identify linear epitopes.

RESULTS

The cloned allergen, designated Ana o 3, was identified as 2S albumin. MALDI-TOF mass spectroscopy of native Ana o 3 yielded a molecular mass of 12,598 d. Immunoblot analysis showed 21 (81%) of 26 sera from patients with cashew allergy were reactive. Three native Ana o 3 large-subunit isoforms with molecular weights ranging from approximately 6 to 10 kd were identified. Probing of overlapping synthetic Ana o 3 peptides with patients' sera identified 16 reactive peptides, 4 of which gave strong signals and one of which positionally overlaps linear epitopes in mustard and walnut allergenic 2S albumins. The overlapping cashew and walnut epitopes also share considerable homology.

CONCLUSIONS

We conclude that this 2S albumin protein is a major allergen in cashew nut and demonstrates a possible basis for cross-reactivity with walnut 2S albumin.

Ty1-copia retrotransposon-based SSAP marker development in cashew (Anacardium occidentale L.)

The most popular retrotransposon-based molecular marker system in use at the present time is the sequence-specific amplification polymorphism (SSAP) system . This system exploits the insertional polymorphism of long terminal repeat (LTR) retrotransposons around the genome. Because the LTR sequence is used to design primers for this method, its successful application requires sequence information from the terminal region of the mobile elements . In this study, two LTR sequences were isolated from the cashew genome and used successfully to develop SSAP marker systems. These were shown to have higher levels of polymorphism than amplified fragment length polymorphic markers for this species.

Molecular detection of cashew husk (Anacardium occidentale) adulteration in market samples of dry tea (Camellia sinensis)

Species-specific PCR primers were developed from intergenic spacer regions of 5S ribosomal RNA genes and used successfully in the detection of adulteration of cashew husk (Anacardium occidentale L.) in tea [Camellia sinensis (L.) O. Kuntze] samples. This is the first report of detecting adulteration in tea using molecular tools. Application of this approach in detecting adulteration of other biological materials in tea, medicinal herbs and the composition of admixtures of ayurvedic herbs has been discussed.

Comparative assessment of DNA fingerprinting techniques (RAPD, ISSR and AFLP) for genetic analysis of cashew (Anacardium occidentale L.) accessions of India

Nineteen cashew accessions were analysed with 50 random primers, 12 ISSR primers and 6 AFLP primer pairs to compare the efficiency and utility of these techniques for detecting variation in cashew germplasm. Each marker system could discriminate between all of the accessions, albeit with varied efficiency of polymorphism detection. AFLP exhibited maximum discrimination efficiency with a genotype index of 1. The utility of each molecular marker technique, expressed as marker index, was estimated as a function of average band informativeness and effective multiplex ratio. Marker index was calculated to be more than 10 times higher in AFLP than in RAPD and ISSR. Similarity matrices were determined based on the data generated by molecular and morphometric analyses, and compared for congruency. AFLP displayed no correspondence with RAPD and ISSR. Correlation between ISSR and RAPD similarity matrices was low but significant (r = 0.63; p < 0.005). The similarity matrix based on morphometric markers exhibited no correlation with any of the molecular markers. AFLP, with its superior marker utility, was concluded to be the marker of choice for cashew genetic analysis.