Bruno Nouy

Regulatory mechanisms underlying oil palm fruit mesocarp maturation, ripening and functional specialization in lipid and carotenoid metabolism

Fruit provide essential nutrients and vitamins for the human diet. Not only is the lipid-rich fleshy mesocarp tissue of the oil palm (Elaeis guineensis) fruit the main source of edible oil for the world, but it is also the richest dietary source of provitamin A. This study examines the transcriptional basis of these two outstanding metabolic characters in the oil palm mesocarp. Morphological, cellular, biochemical, and hormonal features defined key phases of mesocarp development. A 454 pyrosequencing-derived transcriptome was then assembled for the developmental phases preceding and during maturation and ripening, when high rates of lipid and carotenoid biosynthesis occur. A total of 2,629 contigs with differential representation revealed coordination of metabolic and regulatory components. Further analysis focused on the fatty acid and triacylglycerol assembly pathways and during carotenogenesis. Notably, a contig similar to the Arabidopsis (Arabidopsis thaliana) seed oil transcription factor WRINKLED1 was identified with a transcript profile coordinated with those of several fatty acid biosynthetic genes and the high rates of lipid accumulation, suggesting some common regulatory features between seeds and fruits. We also focused on transcriptional regulatory networks of the fruit, in particular those related to ethylene transcriptional and GLOBOSA/PISTILLATA-like proteins in the mesocarp and a central role for ethylene-coordinated transcriptional regulation of type VII ethylene response factors during ripening. Our results suggest that divergence has occurred in the regulatory components in this monocot fruit compared with those identified in the dicot tomato (Solanum lycopersicum) fleshy fruit model.

Geographic and genetic structure of African oil palm diversity suggests new approaches to breeding.

Since the 1960s, there has been very little diversification of oil palm (Elaeis guineensis) seed production, with mainly Deli × La Mé and Deli × Congo type crosses. The Deli origin, which was introduced from Africa into Indonesia in 1848, is unavoidable in breeding. In order to understand the complementarity between the Africa and “Asia” origins, and to diversify the genetic base of oil palm production, the structure of the genetic resources involved in the history of oil palm breeding in relation to African germplasm including subspontaneous populations needs to be understood. In this study, 318 individuals from 26 origins and eight countries were analysed with 14 microsatellite loci. Descriptive and Bayesian analyses of oil palm genetic diversity (Principal Coordinates Analysis, Neighbour-Joining Tree and Structure software) revealed two original groups which reflected the discontinuity of African species at the Dahomey Gap, West Africa (Group I) on the one hand, and “Benin-Nigeria-Cameroon-Congo-Angola” (Group II) on the other hand. The Deli group (Group III), derived from group II, is the result of artificial selection (mass selection). The genetic structuring revealed showed the positive contribution of the within-population mass selection practiced in the Deli population, and explains the success of Deli × La Mé and Deli × Congo crosses. A selection strategy is proposed, based on the yet-to-be-exploited complementarity that exists between the two African genetic groups and on within-group improvement. We suggest (Deli × Group II) × Group I crosses, so that group II benefits from the quality of the Deli origin.

Environmental regulation of sex determination in oil palm: current knowledge and insights from other species

BACKGROUNDnThe African oil palm (Elaeis guineensis) is a monoecious species of the palm subfamily Arecoideae. It may be qualified as temporally dioecious in that it produces functionally unisexual male and female inflorescences in an alternating cycle on the same plant, resulting in an allogamous mode of reproduction. The sex ratio of an oil palm stand is influenced by both genetic and environmental factors. In particular, the enhancement of male inflorescence production in response to water stress has been well documented.nnnSCOPEnThis paper presents a review of our current understanding of the sex determination process in oil palm and discusses possible insights that can be gained from other species. Although some informative phenological studies have been carried out, nothing is as yet known about the genetic basis of sex determination in oil palm, nor the mechanisms by which this process is regulated. Nevertheless new genomics-based techniques, when combined with field studies and biochemical and molecular cytological-based approaches, should provide a new understanding of the complex processes governing oil palm sex determination in the foreseeable future. Current hypotheses and strategies for future research are discussed.

Genomic selection prediction accuracy in a perennial crop: case study of oil palm (Elaeis guineensis Jacq.).

Key messageGenomic selection empirically appeared valuable for reciprocal recurrent selection in oil palm as it could account for family effects and Mendelian sampling terms, despite small populations and low marker density.AbstractGenomic selection (GS) can increase the genetic gain in plants. In perennial crops, this is expected mainly through shortened breeding cycles and increased selection intensity, which requires sufficient GS accuracy in selection candidates, despite often small training populations. Our objective was to obtain the first empirical estimate of GS accuracy in oil palm (Elaeis guineensis), the major world oil crop. We used two parental populations involved in conventional reciprocal recurrent selection (Deli and Group B) with 131 individuals each, genotyped with 265 SSR. We estimated within-population GS accuracies when predicting breeding values of non-progeny-tested individuals for eight yield traits. We used three methods to sample training sets and five statistical methods to estimate genomic breeding values. The results showed that GS could account for family effects and Mendelian sampling terms in Group B but only for family effects in Deli. Presumably, this difference between populations originated from their contrasting breeding history. The GS accuracy ranged from −0.41 to 0.94 and was positively correlated with the relationship between training and test sets. Training sets optimized with the so-called CDmean criterion gave the highest accuracies, ranging from 0.49 (pulp to fruit ratio in Group B) to 0.94 (fruit weight in Group B). The statistical methods did not affect the accuracy. Finally, Group B could be preselected for progeny tests by applying GS to key yield traits, therefore increasing the selection intensity. Our results should be valuable for breeding programs with small populations, long breeding cycles, or reduced effective size.

Quantitative trait loci (QTLs) analysis of palm oil fatty acid composition in an interspecific pseudo-backcross from Elaeis oleifera (H.B.K.) Cortés and oil palm (Elaeis guineensis Jacq.)

We chose an Elaeis interspecific pseudo-backcross of first generation (E. oleifera × E. guineensis) × E. guineensis to identify quantitative trait loci (QTLs) for fatty acid composition of palm oil. A dense microsatellite linkage map of 362 loci spanned 1.485xa0cM, representing the 16 pairs of homologous chromosomes in the Elaeis genus from which we traced segregating alleles from both E. oleifera and E. guineensis grandparents. The relative linear orders of mapped loci suggested the probable absence of chromosome rearrangements between the E. oleifera and E. guineensis genomes. A total of 19 QTL associated to the palm oil fatty acid composition were evidenced. The QTL positions and the species origin as well as the estimated effects of the QTL marker alleles were in coherence with the knowledge of the oil biosynthesis pathway in plants and with the individual phenotypic correlations between the traits. The mapping of chosen Elaeis key genes related to oleic acid C18:1, using intra-gene SNPs, supported several QTLs underlying notably FATA and SAD enzymes. The high number of hyper-variable SSR loci of known relative linear orders and the QTL information make these resources valuable for such mapping study in other Elaeis breeding materials.

Improving palm oil quality through identification and mapping of the lipase gene causing oil deterioration

The oil palm fruit mesocarp contains high lipase activity that increases free fatty acids and necessitates post-harvest inactivation by heat treatment of fruit bunches. Even before heat treatment the mesocarp lipase activity causes consequential oil losses and requires costly measures to limit free fatty acids quantities. Here we demonstrate that elite low-lipase lines yield oil with substantially less free fatty acids than standard genotypes, allowing more flexibility for post-harvest fruit processing and extended ripening for increased yields. We identify the lipase and its gene cosegregates with the low-/high-lipase trait, providing breeders a marker to rapidly identify potent elite genitors and introgress the trait into major cultivars. Overall, economic gains brought by wide adoption of this material could represent up to one billion dollars per year. Expected benefits concern all planters but are likely to be highest for African smallholders who would be more able to produce oil that meets international quality standards.

Multivariate genomic model improves analysis of oil palm (Elaeis guineensis Jacq.) progeny tests

Genomic selection is promising for plant breeding, particularly for perennial crops. Multivariate analysis, which considers several traits jointly, takes advantage of the genetic correlations to increase accuracy. The aim of this study was to empirically evaluate the potential of a univariate and multivariate genomic mixed model (G-BLUP) compared to the traditional univariate pedigree-based BLUP (T-BLUP) when analyzing progeny tests of oil palm, the world’s major oil crop. The dataset comprised 478 crosses between two heterotic groups, A and B, with 140 and 131 parents, respectively, genotyped with 313 simple sequence repeat markers. The traits were bunch number and average bunch weight. We found that G-BLUP with a genomic matrix based on a similarity index gave a higher likelihood than T-BLUP. In addition, multivariate G-BLUP improved the accuracy of additive effects (breeding values or general combining abilities, GCAs), in particular for the less heritable trait, and of dominance effects (specific combining abilities, SCAs). The average increase in accuracy was 22.5xa0% for GCAs and 18.7xa0% for SCAs. Using 160 markers in group A and 90 in group B was enough to reach maximum GCA prediction accuracy. The contrasted history of the parental groups likely explained the higher benefit of G-BLUP over T-BLUP for group A than for group B. Finally, G-BLUP should be used instead of T-BLUP to analyze oil palm progeny tests, with a multivariate approach for correlated traits. G-BLUP will allow breeders to consider SCAs in addition to GCAs when selecting between the progeny-tested parents.

Differential response to water balance and bunch load generates diversity of bunch production profiles among oil palm crosses (Elaeis guineensis).

Oil palm (Elaeis guineensis Jacq.) produces bunches throughout the year, following annual cycles marked by a peak season, with genetic diversity regarding the regularity of the annual profile of bunch production. The aim of this study was to understand this diversity among a set of oil palm crosses. We hypothesized that this diversity originated from differential responses to water balance and bunch load. Seven crosses with different production cycles were studied during 6xa0years in Benin, where dry seasons are marked. Phenological stages of phytomer development were recorded from leaf appearance to bunch harvest. Inequality in the distribution over the months of the year of phytomers at each stage was quantified using the Gini coefficient. We found that annual variations in the rate of early abortions, sex ratio, time between leaf opening and appearance of female inflorescence (AFI) and time between AFI and flowering strongly contributed to the diversity in production profile among crosses. To a lesser extent, annual variations in the time of bunch maturation also generated diversity in the production profile. Sex ratio was positively correlated with water balance and negatively with bunch load when leaves were around axil number -25 (approximately 29xa0months before harvest). Early abortions were positively correlated with bunch load when leaves were at axil number 10 (approximately 9xa0months before harvest). Correlations varied among crosses, indicating differential responses of crosses to variations in water balance and bunch load, which eventually created significant diversity among crosses regarding the regularity of bunch production profiles.

Genomic structure, QTL mapping, and molecular markers of lipase genes responsible for palm oil acidity in the oil palm (Elaeis guineensis Jacq.)

The degradation of triglycerides in oil palm fruit due to an endogenous lipase in the pulp is the main reason for acidification of palm oil, which causes major economic losses and is currently mainly associated with the FLL1 gene. We designed this study to identify all the major genes controlling differences in acidity and lipase activity in the oil palm fruit mesocarp and determine a molecular markers kit to allow marker-assisted selection of commercial varieties with low acidity. Not only one gene (FLL1) but three closely linked genes including FLL1 were found and characterized in LM2T_EgCIR184O12c, a bacterial artificial chromosome sequence of 231xa0kb. Intra-gene PCR-based markers were designed for these genes. A QTL gene co-localization analysis for oil acidity (percentage of fatty acids released) was performed on two mapping populations. It evidenced a single major QTL at our lipase gene loci, explaining 84 to 92% of phenotypic variation, and validating the main genetic control of palm oil acidification by FLL1 and/or by the two new lipase genes. The three lipase genes had high homology to demonstrated triacylglycerol lipases. While FLL1 shows the highest expression levels, the two other genes may also contribute to oil acidity. Our molecular markers of lipase genes and the associated major QTL is an important step towards marker-assisted selection of commercial varieties with low acidity.