The oil palm fruit ‘mantled’ abnormality is a somaclonal variant that markedly reduces yield; here, a genome-wide DNA methylation analysis finds that hypomethylation of a single Karma family retrotransposon embedded in a homeotic gene intron is common to all mantled clones and is associated with aberrant splicing and termination of the gene transcript, and that loss of methylation predicts a loss of oil palm yield. A flower and fruit abnormality known as 'mantled' can develop in some agricultural oil palm cultivars derived from tissue culture and the resulting mantled palms can become unproductive. Mantling is widely regarded as an epigenetic trait, but has not been fully explained. Meilina Ong-Abdullah et al. have undertaken a genome-wide, unbiased, DNA methylation analysis to look for loci epigenetically associated with the mantled phenotype. They find that hypomethylation of a single Karma family retrotransposon embedded in the intron of a homeotic gene is common to all mantled clones and associated with aberrant splicing and termination of the gene transcript. Loss of methylation — dubbed the Bad Karma epiallele — predicts a loss of oil palm yield and this property should enable screening for higher-performing clones at the plantlet stage. Somaclonal variation arises in plants and animals when differentiated somatic cells are induced into a pluripotent state, but the resulting clones differ from each other and from their parents. In agriculture, somaclonal variation has hindered the micropropagation of elite hybrids and genetically modified crops, but the mechanism responsible remains unknown1. The oil palm fruit ‘mantled’ abnormality is a somaclonal variant arising from tissue culture that drastically reduces yield, and has largely halted efforts to clone elite hybrids for oil production2,3,4. Widely regarded as an epigenetic phenomenon5, ‘mantling’ has defied explanation, but here we identify the MANTLED locus using epigenome-wide association studies of the African oil palm Elaeis guineensis. DNA hypomethylation of a LINE retrotransposon related to rice Karma, in the intron of the homeotic gene DEFICIENS, is common to all mantled clones and is associated with alternative splicing and premature termination. Dense methylation near the Karma splice site (termed the Good Karma epiallele) predicts normal fruit set, whereas hypomethylation (the Bad Karma epiallele) predicts homeotic transformation, parthenocarpy and marked loss of yield. Loss of Karma methylation and of small RNA in tissue culture contributes to the origin of mantled, while restoration in spontaneous revertants accounts for non-Mendelian inheritance. The ability to predict and cull mantling at the plantlet stage will facilitate the introduction of higher performing clones and optimize environmentally sensitive land resources.

The commercial oil palm (Elaeis guineensis Jacq.) produces a mesocarp oil (commonly called ‘palm oil’) with approximately equal proportions of saturated and unsaturated fatty acids (FAs). An increase in unsaturated FAs content or iodine value (IV) as a measure of the degree of unsaturation would help to open up new markets for the oil. One way to manipulate the fatty acid composition (FAC) in palm oil is through introgression of favourable alleles from the American oil palm, E. oleifera, which has a more unsaturated oil. In this study, a segregating E. oleifera x E. guineensis (OxG) hybrid population for FAC is used to identify quantitative trait loci (QTLs) linked to IV and various FAs. QTL analysis revealed 10 major and two putative QTLs for IV and six FAs, C14:0, C16:0, C16:1, C18:0, C18:1 and C18:2 distributed across six linkage groups (LGs), OT1, T2, T3, OT4, OT6 and T9. The major QTLs for IV and C16:0 on LGOT1 explained 60.0 – 69.0 % of the phenotypic trait variation and were validated in two independent BC2 populations. The genomic interval contains several key structural genes in the FA and oil biosynthesis pathways such as PATE/FATB, HIBCH, BASS2, LACS4 and DGAT1 and also a relevant transcription factor (TF), WRI1. The literature suggests that some of these genes can exhibit pleiotropic effects in the regulatory networks of these traits. Using the whole genome sequence data, markers tightly linked to the candidate genes were also developed. Clustering trait values according to the allelic forms of these candidate markers revealed significant differences in the IV and FAs of the palms in the mapping and validation crosses. The candidate gene approach described and exploited here is useful to identify the potential causal genes linked to FAC and can be adopted for marker-assisted selection (MAS) in oil palm.

Malaysia's Journal of Oil Palm Research Website

Molecular characterization of oil palm germplasm is crucial in utilizing and conserving germplasm with promising traits. This study was conducted to evaluate the genetic diversity structures and relationships among 26 families of MPOB‐Senegal oil palm germplasm using thirty‐five microsatellite markers. High level of polymorphism (P = 96.26%), number of effective allele (N_e = 2.653), observed heterozygosity (H_o = 0.584), expected heterozygosity (H_e = 0.550), total heterozygosity (H_T = 0.666), and rare alleles (54) were observed which indicates that MPOB‐Senegal germplasm has a broad genetic variation. Among the SSR markers, sMo00053 and sMg00133 were the most informative markers for discrimination among the MPOB‐Senegal oil palm germplasm for having the highest private alleles and the rare alleles. For selection and conservation, oil palm populations with high rare alleles and Nei’s gene diversity index should be considered as these populations may possess unique genes for further exploitation.

Background: Molecular breeding has opened new avenues for crop improvement with the potential for faster progress. As oil palm is the major producer of vegetable oil in the world, its improvement, such as developing compact planting materials and altering its oils’ fatty acid composition for wider application, is important. Results: This study sought to identify the QTLs associated with fatty acid composition and vegetative traits for compactness in the crop. It integrated two interspecific backcross two (BC₂) mapping populations to improve the genetic resolution and evaluate the consistency of the QTLs identified. A total 1963 markers (1814 SNPs and 149 SSRs) spanning a total map length of 1793 cM were integrated into a consensus map. For the first time, some QTLs associated with vegetative parameters and carotene content were identified in interspecific hybrids, apart from those associated with fatty acid composition. The analysis identified 8, 3 and 8 genomic loci significantly associated with fatty acids, carotene content and compactness, respectively. Conclusions: Major genomic region influencing the traits for compactness and fatty acid composition was identified in the same chromosomal region in the two populations using two methods for QTL detection. Several significant loci influencing compactness, carotene content and FAC were common to both populations, while others were specific to particular genetic backgrounds. It is hoped that the QTLs identified will be useful tools for marker-assisted selection and accelerate the identification of desirable genotypes for breeding.