The PIP peptide of INFLORESCENCE DEFICIENT IN ABSCISSION enhances Populus leaf and Elaeis guineensis fruit abscission

The programmed loss of a plant organ is called abscission, which is an important cell separation process that occurs with different organs throughout the life of a plant. The use of floral organ abscission in Arabidopsis thaliana as a model has allowed greater understanding of the complexities of organ abscission, but whether the regulatory pathways are conserved throughout the plant kingdom and for all organ abscission types is unknown. One important pathway that has attracted much attention involves a peptide ligand-receptor signalling system that consists of the secreted peptide IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) and at least two leucine-rich repeat (LRR) receptor-like kinases (RLK), HAESA (HAE) and HAESA-LIKE2 (HSL2). In the current study we examine the bioactive potential of IDA peptides in two different abscission processes, leaf abscission in Populus and ripe fruit abscission in oil palm, and find in both cases treatment with IDA peptides enhances cell separation and abscission of both organ types. Our results provide evidence to suggest that the IDA–HAE–HSL2 pathway is conserved and functions in these phylogenetically divergent dicot and monocot species during both leaf and fruit abscission, respectively

Environmental and trophic determinism of fruit abscission and outlook with climate change in tropical regions

International audienceFruit abscission facilitates the optimal conditions and timing of seed dispersal. Environmental regulation of tropical fruit abscission has received little attention, even though climate change may have its strongest impacts in tropical regions. In this study, oil palm fruit abscission was monitored during multiple years in the Benin Republic to take advantage of the climatic seasonality and the continuous fruit production by this species. An innovative multivariable statistical method was used to identify the best predictors of fruit abscission among a set of climate and ecophysiological variables, and the stage of inflorescence and fruit bunch development when the variables are perceived. The effects of climate scenarios on fruit abscission were then predicted based on the calibrated model. We found complex regulation takes place at specific stages of inflorescence and bunch development, even long before the fruit abscission zone is competent to execute abscission. Among the predictors selected, temperature variations during inflorescence and fruit bunch development are major determinants of the fruit abscission process. Furthermore, the timing of ripe fruit drop is determined by temperature in combination with the trophic status. Finally, climate simulations revealed that the abscission process is robust and is more affected by seasonal variations than by extreme scenarios. Our investigations highlighted the central function of the abscission zone as the sensor of environmental signals during reproductive development. Coupling ecophysiological and statistical modeling was an efficient approach to disentangle this complex environmental regulation. K E Y W O R D S climate change, Elaeis guineensis, environmental regulation, fruit abscission, multivariable model

Improving the accuracy of genomic predictions in an outcrossing species with hybrid cultivars between heterozygote parents: a case study of oil palm (Elaeis guineensis Jacq.)

International audienceGenomic selection (GS) is a method of marker-assisted selection revolutionizing crop improvement, but it can still be optimized. For hybrid breeding between heterozygote parents of different populations or species, specific aspects can be considered to increase GS accuracy: (1) training population genotyping, i.e., only genotyping the hybrid parents or also a sample of hybrid individuals, and (2) marker effects modeling, i.e., using population-specific effects of single nucleotide polymorphism alleles model (PSAM) or across-population SNP genotype model (ASGM). Here, this was investigated empirically for the prediction of the performances of oil palm hybrids for yield traits. The GS model was trained on 352 hybrid crosses and validated on 213 independent hybrid crosses. The training and validation hybrid parents and 399 training hybrid individuals were genotyping by sequencing. Despite the small proportion of hybrid individuals genotyped and low parental heterozygosity, GS prediction accuracy increased on average by 5% (range 1.4-31.3%, depending on trait and model) when training was done using genomic data on hybrids and parents compared with only parental genomic data. With ASGM, GS prediction accuracy increased on average by 3% (- 10.2 to 40%, depending on trait and genotyping strategy) compared with PSAM. We conclude that the best GS strategy for oil palm is to aggregate genomic data of parents and hybrid individuals and to ignore the parental origin of marker alleles (ASGM). To gain a better insight into these results, future studies should examine the respective effect of capturing genetic variability within crosses and taking segregation distortion into account when genotyping hybrid individuals, and investigate the factors controlling the relative performances of ASGM and PSAM in hybrid crops

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

International audienceThe 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 231 kb. 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