Histological and biophysical changes of cassava roots during retting, a key step of fufu processing.

BACKGROUND: Retting is a key step of cassava processing into widely consumed foods (fufu, chikwangue, miondo and bobolo) in sub-Saharan Africa. For some populations, retting ability is a major quality criterion that drives the adoption of new cassava varieties. Despite this importance, the physiological basis associated with this process remains poorly understood, and should lead to improved screening tools for breeding. Eight cassava varieties contrasting in retting ability properties were used in the present study. Roots and soaking water were sampled during retting and characterized at both histological and biochemical levels. RESULTS: Histological data highlighted the degradation of root cell wall during retting. The average pH of soaking water decreased from 5.94 to 4.31 and the average simple sugars decreased from 0.18 to 0 g L-1 , whereas the organic acids increased up to 5.61 g L-1 . In roots tissue, simple sugars and organic acid contents decreased from 22.9 to 0 g kg-1 and from 80 to 0 g kg-1 , respectively. The total pectin content of roots among varieties at harvest was similar, and decreased during the retting process. Overall, there was a negative correlation between total pectins content and root softening, although this did not reach statistical significance. CONCLUSION: Major histological and biochemical changes occurred during cassava root retting, with some of them associated with the process. Retting affected starch pasting properties more than starch content. Although this process is characterized by root softening and degradation of cell wall structure, the present study strongly suggested that pectin is not the only cell wall component involved in these changes. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

User preferences and consumer acceptability of boiled plantain in rural and urban localities in Cameroon.

BACKGROUND: An understanding of the preferences of different stakeholders in the plantain value chain in rural and urban segments in Cameroon is important for the selection and adoption of new plantain cultivars. Boiled plantain is one of the most commonly consumed food products from this crop in Cameroon. Gendered food mapping and consumer testing with two plantain landraces (Batard and Big Ebanga) and a plantain-like hybrid (CARBAP K74) was carried out in rural and urban areas in the West and Littoral regions of Cameroon. RESULTS: Plantain users in these two regions were categorized into producers, traders, processors, and consumers. Preferences indicated that raw plantain should bear long and large fruits, with heavy bunches, and an orange pulp color, whereas boiled plantain should present with a yellow color and a soft and mealy pulp, with a good plantain aroma. Batard and Big Ebanga were liked moderately by consumers, whereas CARBAP K74 was liked slightly. CARBAP K74 was on par with Batard and Big Ebanga for some attributes, except for color and sweetness. CONCLUSION: More emphasis should be given to attributes such as color, firmness, and taste for the development of new plantain clones to be adopted by end users consuming boiled green plantain. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Contrasting effects of polysaccharide components on the cooking properties of roots, tubers and bananas.

BACKGROUND: Consumer preferences for boiled or fried pieces of roots, tubers and bananas (RTBs) are mainly related to their texture. Different raw and cooked RTBs were physiochemically characterized to determine the effect of biochemical components on their cooking properties. RESULTS: Firmness in boiled sweetpotato increases with sugar and amylose contents but no significant correlation was observed between other physicochemical characteristics and cooking behaviour. Hardness of boiled yam can be predicted by dry matter (DM) and galacturonic acid (GalA) levels. For cassava, no significant correlation was found between textural properties of boiled roots and DM, but amylose and Ca2+ content were correlated with firmness, negatively and positively, respectively. Water absorption of cassava root pieces boiled in calcium chloride solutions was much lower, providing indirect evidence that pectins are involved in determining cooking quality. A highly positive correlation between textural attributes and DM was observed for fried plantain, but no significant correlation was found with GalA, although frying slightly reduced GalA. CONCLUSION: The effect of main components on texture after cooking differs for the various RTBs. The effect of global DM and major components (i.e. starch, amylose) is prominent for yam, plantain and sweetpotato. Pectins also play an important role on the texture of boiled yam and play a prominent role for cassava through interaction with Ca2+ . © 2023 Bill and Melinda Gates Foundation. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Lineage-Specific Evolutionary Histories and Regulation of Major Starch Metabolism Genes during Banana Ripening.

Starch is the most widespread and abundant storage carbohydrate in plants. It is also a major feature of cultivated bananas as it accumulates to large amounts during banana fruit development before almost complete conversion to soluble sugars during ripening. Little is known about the structure of major gene families involved in banana starch metabolism and their evolution compared to other species. To identify genes involved in banana starch metabolism and investigate their evolutionary history, we analyzed six gene families playing a crucial role in plant starch biosynthesis and degradation: the ADP-glucose pyrophosphorylases (AGPases), starch synthases (SS), starch branching enzymes (SBE), debranching enzymes (DBE), α-amylases (AMY) and ß-amylases (BAM). Using comparative genomics and phylogenetic approaches, these genes were classified into families and sub-families and orthology relationships with functional genes in Eudicots and in grasses were identified. In addition to known ancestral duplications shaping starch metabolism gene families, independent evolution in banana and grasses also occurred through lineage-specific whole genome duplications for specific sub-families of AGPase, SS, SBE, and BAM genes; and through gene-scale duplications for AMY genes. In particular, banana lineage duplications yielded a set of AGPase, SBE and BAM genes that were highly or specifically expressed in banana fruits. Gene expression analysis highlighted a complex transcriptional reprogramming of starch metabolism genes during ripening of banana fruits. A differential regulation of expression between banana gene duplicates was identified for SBE and BAM genes, suggesting that part of starch metabolism regulation in the fruit evolved in the banana lineage.

Nitrogen fixation in a chemoautotrophic lucinid symbiosis.

The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2 and thus generates organic carbon compounds, which support the host's growth. To investigate the uncultured symbiont's metabolism and symbiont-host interactions in detail we conducted a proteogenomic analysis of purified bacteria. Unexpectedly, our results reveal a hitherto completely unrecognized feature of the C. orbicularis symbiont's physiology: the symbiont's genome encodes all proteins necessary for biological nitrogen fixation (diazotrophy). Expression of the respective genes under standard ambient conditions was confirmed by proteomics. Nitrogenase activity in the symbiont was also verified by enzyme activity assays. Phylogenetic analysis of the bacterial nitrogenase reductase NifH revealed the symbiont's close relationship to free-living nitrogen-fixing Proteobacteria from the seagrass sediment. The C. orbicularis symbiont, here tentatively named 'Candidatus Thiodiazotropha endolucinida', may thus not only sustain the bivalve's carbon demands. C. orbicularis may also benefit from a steady supply of fixed nitrogen from its symbiont-a scenario that is unprecedented in comparable chemoautotrophic symbioses.

Expansion of banana (Musa acuminata) gene families involved in ethylene biosynthesis and signalling after lineage-specific whole-genome duplications.

Whole-genome duplications (WGDs) are widespread in plants, and three lineage-specific WGDs occurred in the banana (Musa acuminata) genome. Here, we analysed the impact of WGDs on the evolution of banana gene families involved in ethylene biosynthesis and signalling, a key pathway for banana fruit ripening. Banana ethylene pathway genes were identified using comparative genomics approaches and their duplication modes and expression profiles were analysed. Seven out of 10 banana ethylene gene families evolved through WGD and four of them (1-aminocyclopropane-1-carboxylate synthase (ACS), ethylene-insensitive 3-like (EIL), ethylene-insensitive 3-binding F-box (EBF) and ethylene response factor (ERF)) were preferentially retained. Banana orthologues of AtEIN3 and AtEIL1, two major genes for ethylene signalling in Arabidopsis, were particularly expanded. This expansion was paralleled by that of EBF genes which are responsible for control of EIL protein levels. Gene expression profiles in banana fruits suggested functional redundancy for several MaEBF and MaEIL genes derived from WGD and subfunctionalization for some of them. We propose that EIL and EBF genes were co-retained after WGD in banana to maintain balanced control of EIL protein levels and thus avoid detrimental effects of constitutive ethylene signalling. In the course of evolution, subfunctionalization was favoured to promote finer control of ethylene signalling.

Changes in antioxidant activity during the ripening of jujube (Ziziphus mauritiana Lamk).

Phenolic compounds from jujube fruits and related antioxidant activities were investigated during the ripening stages. Three different antioxidant assays, including ORAC, FRAP and DPPH, were monitored on crude jujube extract (CJE). Jujube fruits were additionally fractionated into three selective fractions F1, F2, and F3. However, only the FRAP assay gave the relative antioxidant activity for the three fractions. Furthermore, HPLC-ESI-MSMS (Q-Tof) and GC-MS were used to identify the compounds in each purified fraction. Using FRAP, F1 mainly composed of lipids, exhibited the lowest antioxidant activity (≈0.080±0.015mmol trolox/100g, p<0.05). F2, rich in flavanols and flavonols, displayed 50-fold higher activity (4.27±0.11mmol trolox/100g). Remarkably, F3 with an elevated content of condensed tannins (polymeric proanthodelphinidins), exhibited the highest antioxidant activity (25.4±0.35mmol trolox/100g). The presented results showed that the phenolic profiles of the fruits were influenced by their developmental stage. Furthermore, during ripening, the antioxidant activity may be more impacted by the flavanols and condensed tannins. The purified condensed tannins of jujube fruits may be used as natural antioxidant extracts.

Effect of physiological harvest stages on the composition of bioactive compounds in Cavendish bananas.

The combined influence of maturation, ripening, and climate on the profile of bioactive compounds was studied in banana (Musa acuminata, AAA, Cavendish, cv. Grande Naine). Their bioactive compounds were determined by the Folin-Ciocalteu assay and high-performance thin layer chromatographic (HPTLC) method. The polyphenol content of bananas harvested after 400 degree days remained unchanged during ripening, while bananas harvested after 600 and 900 degree days exhibited a significant polyphenol increase. Although dopamine was the polyphenol with the highest concentration in banana peels during the green developmental stage and ripening, its kinetics differed from the total polyphenol profile. Our results showed that this matrix of choice (maturation, ripening, and climate) may allow selection of the banana (M. acuminata, AAA, Cavendish, cv. Grande Naine) status that will produce optimal concentrations of identified compounds with human health relevance.

Expression patterns of ethylene biosynthesis genes from bananas during fruit ripening and in relationship with finger drop.

BACKGROUND AND AIMS: Banana finger drop is defined as dislodgement of individual fruits from the hand at the pedicel rupture area. For some banana varieties, this is a major feature of the ripening process, in addition to ethylene production and sugar metabolism. The few studies devoted to assessing the physiological and molecular basis of this process revealed (i) the similarity between this process and softening, (ii) the early onset of related molecular events, between the first and fourth day after ripening induction, and (iii) the putative involvement of ethylene as a regulatory factor. This study was conducted with the aim of identifying, through a candidate gene approach, a quality-related marker that could be used as a tool in breeding programmes. Here we examined the relationship between ripening ethylene biosynthesis (EB) and finger drop in order to gain further insight into the upstream regulatory steps of the banana finger drop process and to identify putative related candidate genes. METHODS: Postharvest ripening of green banana fruit was induced by acetylene treatment and fruit taken at 1-4 days after ripening induction, and total RNA extracted from the median area [control zone (CZ)] and the pedicel rupture area [drop zone (DZ)] of peel tissue. Then the expression patterns of EB genes (MaACO1, MaACO2, MaACS1, MaACS2, MaACS3 and MaACS4) were comparatively examined in CZ and DZ via real-time quantitative polymerase chain reaction. PRINCIPAL RESULTS: Differential expression of EB gene was observed in CZ and DZ during the postharvest period examined in this study. MaACO1, MaACS2 and MaACS1 were more highly induced in DZ than in the control, while a slight induction of the MaACS4 gene was observed. No marked differences between the two zones were observed for the MaACO2 gene. CONCLUSIONS: The finger drop process enhanced EB gene expression including developmental- and ripening-induced genes (MaACO1), specific ripening-induced genes (MaACS1) and wound-induced genes (MaACS2). Thus, this process might be associated with a specific ethylene production in DZ of the pedicel area and the result of crosstalk between developmental, ripening and wound regulatory pathways. MaACO1, MaACS1, MaACS2, and to a lesser extent MaACS4 genes, which are more highly induced in DZ than in CZ, could be considered as putative candidates of the finger drop process.

The banana (Musa acuminata) genome and the evolution of monocotyledonous plants.

Bananas (Musa spp.), including dessert and cooking types, are giant perennial monocotyledonous herbs of the order Zingiberales, a sister group to the well-studied Poales, which include cereals. Bananas are vital for food security in many tropical and subtropical countries and the most popular fruit in industrialized countries. The Musa domestication process started some 7,000 years ago in Southeast Asia. It involved hybridizations between diverse species and subspecies, fostered by human migrations, and selection of diploid and triploid seedless, parthenocarpic hybrids thereafter widely dispersed by vegetative propagation. Half of the current production relies on somaclones derived from a single triploid genotype (Cavendish). Pests and diseases have gradually become adapted, representing an imminent danger for global banana production. Here we describe the draft sequence of the 523-megabase genome of a Musa acuminata doubled-haploid genotype, providing a crucial stepping-stone for genetic improvement of banana. We detected three rounds of whole-genome duplications in the Musa lineage, independently of those previously described in the Poales lineage and the one we detected in the Arecales lineage. This first monocotyledon high-continuity whole-genome sequence reported outside Poales represents an essential bridge for comparative genome analysis in plants. As such, it clarifies commelinid-monocotyledon phylogenetic relationships, reveals Poaceae-specific features and has led to the discovery of conserved non-coding sequences predating monocotyledon-eudicotyledon divergence.

Sensory characterisation enabled the first classification of dessert bananas.

BACKGROUND: Knowledge of the sensory diversity of a wide range of dessert bananas would be helpful in breeding programmes and so diversify the banana market. Descriptive sensory profiling was thus used to assess 13 cultivated bananas and four new triploid hybrids at an eating stage. RESULTS: A specific vocabulary was defined to describe the sensory traits of dessert bananas. The 17 cultivars assessed were ranked in five sensory clusters, which differed mainly in the intensity of sourness and sweetness. The first cluster, which contained the standard banana (Cavendish), received the lowest sourness and the highest sweetness and banana flavour scores. The second cluster was the sourest and firmest and had the highest chemical flavour score. The third cluster was characterised by the highest melting score, the fourth by the highest mealiness, astringency, grassy odour and flavour scores and the fifth by a balance between sourness and sweetness and the highest heterogeneous texture score. Firmness and sourness were correlated with rheological pulp firmness and titratable acidity respectively. CONCLUSION: The results led to the identification of relevant attributes that grouped the sensory diversity of dessert banana into five clusters. Combined with hedonic data, these results should help breeders to select banana hybrids.

Mechanisms of haplotype divergence at the RGA08 nucleotide-binding leucine-rich repeat gene locus in wild banana (Musa balbisiana).

BACKGROUND: Comparative sequence analysis of complex loci such as resistance gene analog clusters allows estimating the degree of sequence conservation and mechanisms of divergence at the intraspecies level. In banana (Musa sp.), two diploid wild species Musa acuminata (A genome) and Musa balbisiana (B genome) contribute to the polyploid genome of many cultivars. The M. balbisiana species is associated with vigour and tolerance to pests and disease and little is known on the genome structure and haplotype diversity within this species. Here, we compare two genomic sequences of 253 and 223 kb corresponding to two haplotypes of the RGA08 resistance gene analog locus in M. balbisiana "Pisang Klutuk Wulung" (PKW). RESULTS: Sequence comparison revealed two regions of contrasting features. The first is a highly colinear gene-rich region where the two haplotypes diverge only by single nucleotide polymorphisms and two repetitive element insertions. The second corresponds to a large cluster of RGA08 genes, with 13 and 18 predicted RGA genes and pseudogenes spread over 131 and 152 kb respectively on each haplotype. The RGA08 cluster is enriched in repetitive element insertions, in duplicated non-coding intergenic sequences including low complexity regions and shows structural variations between haplotypes. Although some allelic relationships are retained, a large diversity of RGA08 genes occurs in this single M. balbisiana genotype, with several RGA08 paralogs specific to each haplotype. The RGA08 gene family has evolved by mechanisms of unequal recombination, intragenic sequence exchange and diversifying selection. An unequal recombination event taking place between duplicated non-coding intergenic sequences resulted in a different RGA08 gene content between haplotypes pointing out the role of such duplicated regions in the evolution of RGA clusters. Based on the synonymous substitution rate in coding sequences, we estimated a 1 million year divergence time for these M. balbisiana haplotypes. CONCLUSIONS: A large RGA08 gene cluster identified in wild banana corresponds to a highly variable genomic region between haplotypes surrounded by conserved flanking regions. High level of sequence identity (70 to 99%) of the genic and intergenic regions suggests a recent and rapid evolution of this cluster in M. balbisiana.

A saturated SSR/DArT linkage map of Musa acuminata addressing genome rearrangements among bananas.

BACKGROUND: The genus Musa is a large species complex which includes cultivars at diploid and triploid levels. These sterile and vegetatively propagated cultivars are based on the A genome from Musa acuminata, exclusively for sweet bananas such as Cavendish, or associated with the B genome (Musa balbisiana) in cooking bananas such as Plantain varieties. In M. acuminata cultivars, structural heterozygosity is thought to be one of the main causes of sterility, which is essential for obtaining seedless fruits but hampers breeding. Only partial genetic maps are presently available due to chromosomal rearrangements within the parents of the mapping populations. This causes large segregation distortions inducing pseudo-linkages and difficulties in ordering markers in the linkage groups. The present study aims at producing a saturated linkage map of M. acuminata, taking into account hypotheses on the structural heterozygosity of the parents. RESULTS: An F1 progeny of 180 individuals was obtained from a cross between two genetically distant accessions of M. acuminata, 'Borneo' and 'Pisang Lilin' (P. Lilin). Based on the gametic recombination of each parent, two parental maps composed of SSR and DArT markers were established. A significant proportion of the markers (21.7%) deviated (p < 0.05) from the expected Mendelian ratios. These skewed markers were distributed in different linkage groups for each parent. To solve some complex ordering of the markers on linkage groups, we associated tools such as tree-like graphic representations, recombination frequency statistics and cytogenetical studies to identify structural rearrangements and build parsimonious linkage group order. An illustration of such an approach is given for the P. Lilin parent. CONCLUSIONS: We propose a synthetic map with 11 linkage groups containing 489 markers (167 SSRs and 322 DArTs) covering 1197 cM. This first saturated map is proposed as a "reference Musa map" for further analyses. We also propose two complete parental maps with interpretations of structural rearrangements localized on the linkage groups. The structural heterozygosity in P. Lilin is hypothesized to result from a duplication likely accompanied by an inversion on another chromosome. This paper also illustrates a methodological approach, transferable to other species, to investigate the mapping of structural rearrangements and determine their consequences on marker segregation.

EIN3-like gene expression during fruit ripening of Cavendish banana (Musa acuminata cv. Grande naine).

Ethylene signal transduction initiates with ethylene binding at receptor proteins and terminates in a transcription cascade involving the EIN3/EIL transcription factors. Here, we have isolated four cDNAs homologs of the Arabidopsis EIN3/EIN3-like gene, MA-EILs (Musa acuminata ethylene insensitive 3-like) from banana fruit. Sequence comparison with other banana EIL gene already registered in the database led us to conclude that, at this day, at least five different genes namely MA-EIL1, MA-EIL2/AB266318, MA-EIL3/AB266319, MA-EIL4/AB266320 and AB266321 exist in banana. Phylogenetic analyses included all banana EIL genes within a same cluster consisting of rice OsEILs, a monocotyledonous plant as banana. However, MA-EIL1, MA-EIL2/AB266318, MA-EIL4/AB266320 and AB266321 on one side, and MA-EIL3/AB266319 on the other side, belong to two distant subclusters. MA-EIL mRNAs were detected in all examined banana tissues but at lower level in peel than in pulp. According to tissues, MA-EIL genes were differentially regulated by ripening and ethylene in mature green fruit and wounding in old and young leaves. MA-EIL2/AB266318 was the unique ripening- and ethylene-induced gene; MA-EIL1, MA-EIL4/Ab266320 and AB266321 genes were downregulated, while MA-EIL3/AB266319 presented an unusual pattern of expression. Interestingly, a marked change was observed mainly in MA-EIL1 and MA-EIL3/Ab266319 mRNA accumulation concomitantly with changes in ethylene responsiveness of fruit. Upon wounding, the main effect was observed in MA-EIL4/AB266320 and AB266321 mRNA levels, which presented a markedly increase in both young and old leaves, respectively. Data presented in this study suggest the importance of a transcriptionally step control in the regulation of EIL genes during banana fruit ripening.