The effects of palm kernel cake (PKC) as a protein source in a concentrate diet (comprising 35 % crushed maize, 30 % rice bran, 32 % PKC, 2 % vitamin mineral premix and 1 % salt) were examined on intake, live weight (LW) gain and digestibility in female goats (average LW of 12.4 ± 2.6 kg). Four goats were randomly allocated to each of the four treatment diets: (a) Napier grass (Pennisetum purpureum) offered ad libitum (T1), (b) T1 + concentrate at 0.5 % of LW (T2), (c) T1 + concentrate at 1.0 % of LW (T3) and (d) T1 + concentrate at 2.0 % of LW (T4). A 7-day digestibility trial and an 82-day growth experiment were conducted. No differences were observed among diets for intakes of roughage dry matter (DM), total DM, organic matter (OM) and neutral detergent fibre (NDF). The crude protein (CP) intake increased (P 0.05) among treatments. The digestibility of dietary NDF decreased (P 0.05) difference between T2 and T3 diets. Supplementing a basal diet of Napier grass with PKC-based concentrate improved CP intake and LW gain. The PKC-based concentrate diet can therefore be exploited for the use of local feed resources for goat production; however, further research is required to achieve the best growth response.
Proteomics technologies were first applied in the oil palm research back in 2008. Since proteins are the gene products that are directly correspond to phenotypic traits, proteomic tools hold a strong advantage above other molecular tools to comprehend the biological and molecular mechanisms in the oil palm system. These emerging technologies have been used as non-overlapping tools to link genome-wide transcriptomics and metabolomics-based studies to enhance the oil palm yield and quality through sustainable plant breeding. Many efforts have also been made using the proteomics technologies to address the oil palm's Ganoderma disease; the cause and management. At present, the high-throughput screening technologies are being applied to identify potential biomarkers involved in metabolism and cellular development through determination of protein expression changes that correlate with oil production and disease. This review highlights key elements in proteomics pipeline, challenges and some examples of their implementations in plant studies in the context of oil palm in particular. We foresee that the proteomics technologies will play more significant role to address diverse issues related to the oil palm in the effort to improve the oil crop.
The details of plant lipid metabolism are relatively well known but the regulation of fatty acid production at the protein level is still not understood. Hence this study explores the importance of phosphorylation as a mechanism to control the activity of fatty acid biosynthetic enzymes using low and high oleic acid mesocarps of oil palm fruit (Elaeis guineensis variety of Tenera). Adaptation of neutral loss-triggered tandem mass spectrometry and selected reaction monitoring to detect the neutral loss of phosphoric acid successfully found several phosphoamino acid-containing peptides. These peptides corresponded to the peptides from acetyl-CoA carboxylase and 3-enoyl-acyl carrier protein reductase as identified by their precursor ion masses. These findings suggest that these enzymes were phosphorylated at 20th week after anthesis. Phosphorylation could have reduce their activities towards the end of fatty acid biosynthesis at ripening stage. Implication of phosphorylation in the regulation of fatty acid biosynthesis at protein level has never been reported.
The oil biosynthesis pathway must be tightly controlled to maximize oil yield. Oil palm accumulates exceptionally high oil content in its mesocarp, suggesting the existence of a unique fruit-specific fatty acid metabolism transcriptional network. We report the complex fruit-specific network of transcription factors responsible for modulation of oil biosynthesis genes in oil palm mesocarp. Transcriptional activation of EgWRI1-1 encoding a key master regulator that activates expression of oil biosynthesis genes, is activated by three ABA-responsive transcription factors, EgNF-YA3, EgNF-YC2 and EgABI5. Overexpression of EgWRI1-1 and its activators in Arabidopsis accelerated flowering, increased seed size and oil content, and altered expression levels of oil biosynthesis genes. Protein-protein interaction experiments demonstrated that EgNF-YA3 interacts directly with EgWRI1-1, forming a transcription complex with EgNF-YC2 and EgABI5 to modulate transcription of oil biosynthesis pathway genes. Furthermore, EgABI5 acts downstream of EgWRKY40, a repressor that interacts with EgWRKY2 to inhibit the transcription of oil biosynthesis genes. We showed that expression of these activators and repressors in oil biosynthesis can be induced by phytohormones coordinating fruit development in oil palm. We propose a model highlighting a hormone signaling network coordinating fruit development and fatty acid biosynthesis.
Oil palm is an important crop for global vegetable oil production, and is widely grown in the humid tropical regions of Southeast Asia. Projected future climate change may well threaten palm oil production. However, oil palm plantations currently produce large amounts of unutilised biological waste. Oil palm stems - which comprise two-thirds of the waste - are especially relevant because they can contain high levels of non-structural carbohydrates (NSC) that can serve as feedstock for biorefineries. The NSC in stem are also considered a potent buffer to source-sink imbalances. In the present study, we monitored stem NSC levels and female reproductive growth. We then applied convergent cross mapping (CCM) to assess the causal relationship between the time-series. Mutual causal relationships between female reproductive growth and the stem NSC were detected, with the exception of a relationship between female reproductive organ growth and starch levels. The NSC levels were also influenced by long-term cumulative temperature, with the relationship showing a seven-month time lag. The dynamic between NSC levels and long-term cumulative rainfall showed a shorter time lag. The lower temperatures and higher cumulative rainfall observed from October to December identify this as a period with maximum stem NSC stocks.
Evaluation of transcriptome data in combination with QTL information has been applied in many crops to study the expression of genes responsible for specific phenotypes. In oil palm, the mesocarp oil extracted from E. oleifera × E. guineensis interspecific hybrids is known to have lower palmitic acid (C16:0) content compared to pure African palms. The present study demonstrates the effectiveness of transcriptome data in revealing the expression profiles of genes in the fatty acid (FA) and triacylglycerol (TAG) biosynthesis processes in interspecific hybrids. The transcriptome assembly yielded 43,920 putative genes of which a large proportion were homologous to known genes in the public databases. Most of the genes encoding key enzymes involved in the FA and TAG synthesis pathways were identified. Of these, 27, including two candidate genes located within the QTL associated with C16:0 content, showed differential expression between developmental stages, populations and/or palms with contrasting C16:0 content. Further evaluation using quantitative real-time PCR revealed that differentially expressed patterns are generally consistent with those observed in the transcriptome data. Our results also suggest that different isoforms are likely to be responsible for some of the variation observed in FA composition of interspecific hybrids.
The fructose-1,6-bisphosphate aldolase catalyzed glycolysis branch that forms dihydroxyacetone phosphate and glyceraldehyde-3-phosphate was identified as a key driver of increased oil synthesis in oil palm and was validated in Saccharomyces cerevisiae. Reduction in triose phosphate isomerase (TPI) activity in a yeast knockdown mutant resulted in 19% increase in lipid content, while yeast strains overexpressing oil palm fructose-1,6-bisphosphate aldolase (EgFBA) and glycerol-3-phosphate dehydrogenase (EgG3PDH) showed increased lipid content by 16% and 21%, respectively. Genetic association analysis on oil palm SNPs of EgTPI SD_SNP_000035801 and EgGAPDH SD_SNP_000041011 showed that palms harboring homozygous GG in EgTPI and heterozygous AG in EgGAPDH exhibited higher mesocarp oil content based on dry weight. In addition, AG genotype of the SNP of EgG3PDH SD_SNP_000008411 was associated with higher mean mesocarp oil content, whereas GG genotype of the EgFBA SNP SD_SNP_000007765 was favourable. Additive effects were observed with a combination of favourable alleles in TPI and FBA in Nigerian x AVROS population (family F7) with highest allele frequency GG.GG being associated with a mean increase of 3.77% (p value = 2.3E-16) oil content over the Family 1. An analogous effect was observed in yeast, where overexpressed EgFBA in TPI - resulted in a 30% oil increment. These results provide insights into flux balances in glycolysis leading to higher yield in mesocarp oil-producing fruit.
Plant defensins are plant defence peptides that have many different biological activities, including antifungal, antimicrobial, and insecticidal activities. A cDNA (EgDFS) encoding defensin was isolated from Elaeis guineensis. The open reading frame of EgDFS contained 231 nucleotides encoding a 71-amino acid protein with a predicted molecular weight at 8.69 kDa, and a potential signal peptide. The eight highly conserved cysteine sites in plant defensins were also conserved in EgDFS. The EgDFS sequence lacking 30 amino acid residues at its N-terminus (EgDFSm) was cloned into Escherichia coli BL21 (DE3) pLysS and successfully expressed as a soluble recombinant protein. The recombinant EgDFSm was found to be a thermal stable peptide which demonstrated inhibitory activity against the growth of G. boninense possibly by inhibiting starch assimilation. The role of EgDFSm in oil palm defence system against the infection of pathogen G. boninense was discussed.
Lowland tropical forests are increasingly threatened with conversion to oil palm as global demand and high profit drives crop expansion throughout the world's tropical regions. Yet, landscapes are not homogeneous and regional constraints dictate land suitability for this crop. We conducted a regional study to investigate spatial and economic components of forest conversion to oil palm within a tropical floodplain in the Lower Kinabatangan, Sabah, Malaysian Borneo. The Kinabatangan ecosystem harbours significant biodiversity with globally threatened species but has suffered forest loss and fragmentation. We mapped the oil palm and forested landscapes (using object-based-image analysis, classification and regression tree analysis and on-screen digitising of high-resolution imagery) and undertook economic modelling. Within the study region (520,269 ha), 250,617 ha is cultivated with oil palm with 77% having high Net-Present-Value (NPV) estimates ($413/ha-yr-$637/ha-yr); but 20.5% is under-producing. In fact 6.3% (15,810 ha) of oil palm is commercially redundant (with negative NPV of $-299/ha-yr-$-65/ha-yr) due to palm mortality from flood inundation. These areas would have been important riparian or flooded forest types. Moreover, 30,173 ha of unprotected forest remain and despite its value for connectivity and biodiversity 64% is allocated for future oil palm. However, we estimate that at minimum 54% of these forests are unsuitable for this crop due to inundation events. If conversion to oil palm occurs, we predict a further 16,207 ha will become commercially redundant. This means that over 32,000 ha of forest within the floodplain would have been converted for little or no financial gain yet with significant cost to the ecosystem. Our findings have globally relevant implications for similar floodplain landscapes undergoing forest transformation to agriculture such as oil palm. Understanding landscape level constraints to this crop, and transferring these into policy and practice, may provide conservation and economic opportunities within these seemingly high opportunity cost landscapes.
To investigate limiters of photosynthate assimilation in the carbon-source limited crop, oil palm (Elaeis guineensis Jacq.), we measured differential metabolite, gene expression and the gas exchange in leaves in an open field for palms with distinct mesocarp oil content. We observed higher concentrations of glucose 1-phosphate, glucose 6-phosphate, sucrose 6-phosphate, and sucrose in high-oil content palms with the greatest difference being at 11:00 (p-value ≤0.05) immediately after the period of low morning light intensity. Three important photosynthetic genes were identified using differentially expressed gene analysis (DEGs) and were found to be significantly enriched through Gene Ontology (GO) and pathway enrichment: chlorophyll a-b binding protein (CAB-13), photosystem I (PSI), and Ferredoxin-NADP reductase (FNR), particularly for sampling points at non-peak light (11:00 and 19:00), ranging from 3.3-fold (PSI) and 5.6-fold (FNR) to 10.3-fold (CAB-13). Subsequent gas exchange measurements further supported increased carbon assimilation through higher level of internal CO2 concentration (Ci), stomatal conductance (gs) and transpiration rate (E) in high-oil content palms. The selection for higher expression of key photosynthesis genes together with CO2 assimilation under low light is likely to be important for crop improvement, in particular at full maturity and under high density planting regimes where light competition exists between palms.
Palm kernel cake (PKC) is the main byproduct from the palm oil industry in several tropical countries that contains considerable amounts of oligosaccharide. We earlier demonstrated beneficial prebiotic effects of oligosaccharides extract of PKC (OligoPKC) in starter and finisher broiler birds. This study was envisaged to elucidate the effects of in ovo and/or oral administration of the OligoPKC on prenatal and post-hatched broiler chicks. A total of 140 broiler (Cobb500) eggs were randomly divided into two groups (n = 70 each), and on day 12 of incubation, eggs in one group received in ovo injection of 0.1 mL (containing 20 mg) of OligoPKC, while those in the other group received 0.1 mL of saline (placebo) solution. Of these in ovo placebo or OligoPKC injected eggs, after hatching, six chicks from each group were sampled for day-one analysis, while 48 chicks from each group were randomly allocated to two dietary regimes involving either no feeding or feeding of OligoPKC through basal diet for a 14 days experiment forming the experimental groups as: (i) saline-injected (Control, C), (ii) OligoPKC-injected (PREBovo), (iii) saline-injected, but fed 1% OligoPKC (PREBd), and (iv) OligoPKC-injected and also 1% OligoPKC (PREBovo+d). In ovo injection of prebiotic OligoPKC had no effect on body weight and serum immunoglobulins concentrations of day old chicks, except for IgG, which was increased significantly (P<0.05). Body weight and feed conversion ratio of 14 days old chicks were neither affected by in ovo injection nor feeding of OligoPKC. However, populations of cecal total bacteria and major beneficial bacteria of the chicks were markedly enhanced by feeding of OligoPKC (PREBd and PREBovo+d > C and PREBovo), but lesser influenced by in ovo OligoPKC injection. Irrespective of its prior in ovo exposure, chicks fed OligoPKC diets had lower population of pathogenic bacteria. Overall serum immunoglobulin status of birds was improved by feeding of OligoPKC but in ovo OligoPKC injection had minor effect on that. In most cases, in ovo OligoPKC injection and feeding of OligoPKC reduced the expression of nutrient transporters in the intestine and improved antioxidant capacity of liver and serum. It is concluded that in ovo injection of OligoPKC increased IgG production and antioxidant capacity in serum and liver of prenatal chicks and had limited carrying-over effects on the post-hatched chicks comparing to the supplementary feeding of OligoPKC.
To better understand lipid biosynthesis in oil palm mesocarp, in particular the differences in gene regulation leading to and including de novo fatty acid biosynthesis, a multi-platform metabolomics technology was used to profile mesocarp metabolites during six critical stages of fruit development in comparatively high- and low-yielding oil palm populations. Significantly higher amino acid levels preceding lipid biosynthesis and nucleosides during lipid biosynthesis were observed in a higher yielding commercial palm population. Levels of metabolites involved in glycolysis revealed interesting divergence of flux towards glycerol-3-phosphate, while carbon utilization differences in the TCA cycle were proven by an increase in malic acid/citric acid ratio. Apart from insights into the regulation of enhanced lipid production in oil palm, these results provide potentially useful metabolite yield markers and genes of interest for use in breeding programmes.
Polyhydroxybutyrate-co-hydroxyvalerate (PHBV) is a polyhydroxyalkanoate (PHA) bioplastic group with thermoplastic properties is thus high in quality and can be degradable. PHBV can be produced by bacteria, but the process is not economically competitive with polymers produced from petrochemicals. To overcome this problem, research on transgenic plants has been carried out as one of the solutions to produce PHBV in economically sound alternative manner. Four different genes encoded with the enzymes necessary to catalyze PHBV are bktB, phaB, phaC and tdcB. All the genes came with modified CaMV 35S promoters (except for the tdcB gene, which was promoted by the native CaMV 35S promoter), nos terminator sequences and plastid sequences in order to target the genes into the plastids. Subcloning resulted in the generation of two different orientations of the tdcB, pLMIN (left) and pRMIN (right), both 17.557 and 19.967 kb in sizes. Both plasmids were transformed in immature embryos (IE) of oil palm via Agrobacterium tumefaciens. Assays of GUS were performed on one-week-old calli and 90% of the calli turned completely blue. This preliminary test showed positive results of integration. Six-months-old calli were harvested and RNA of the calli were isolated. RT-PCR was used to confirm the transient expression of PHBV transgenes in the calli. The bands were 258, 260, 315 and 200 bp in size for bktB, phaB, phaC and tdcB transgenes respectively. The data obtained showed that the bktB, phaB, phaC and tdcB genes were successfully integrated and expressed in the oil palm genome.
One of the targets in oil palm genetic engineering programme is the production of polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) in the oil palm leaf tissues. Production of PHB requires the use of phbA (beta-ketothiolase type A), phbB (acetoacetyl-CoA reductase) and phbC (PHB synthase) genes of Ralstonia eutropha, whereas bktB (beta-ketothiolase type B), phbB, phbC genes of R. eutropha and tdcB (threonine dehydratase) gene of Escherichia coli were used for PHBV production. Each of these genes was fused with a transit peptide (Tp) of oil palm acyl-carrier-protein (ACP) gene, driven by an oil palm leaf-specific promoter (LSP1) to genetically engineer the PHB/PHBV pathway to the plastids of the leaf tissues. In total, four transformation vectors, designated pLSP15 (PHB) and pLSP20 (PHBV), and pLSP13 (PHB) and pLSP23 (PHBV), were constructed for transformation in Arabidopsis thaliana and oil palm, respectively. The phosphinothricin acetyltransferase gene (bar) driven by CaMV35S promoter in pLSP15 and pLSP20, and ubiquitin promoter in pLSP13 and pLSP23 were used as the plant selectable markers. Matrix attachment region of tobacco (RB7MAR) was also included in the vectors to stabilize the transgene expression and to minimize silencing due to positional effect. Restriction digestion, PCR amplification and/or sequencing were carried out to ensure sequence integrity and orientation.
The 1,053-bp promoter of the oil palm metallothionein gene (so-called MSP1) and its 5' deletions were fused to the GUS reporter gene, and analysed in transiently transformed oil palm tissues. The full length promoter showed sevenfold higher activity in the mesocarp than in leaves and 1.5-fold more activity than the CaMV35S promoter in the mesocarp. The 1,053-bp region containing the 5' untranslated region (UTR) gave the highest activity in the mesocarp, while the 148-bp region was required for minimal promoter activity. Two positive regulatory regions were identified at nucleotides (nt) -953 to -619 and -420 to -256 regions. Fine-tune deletion of the -619 to -420 nt region led to the identification of a 21-bp negative regulatory sequence in the -598 to -577 nt region, which is involved in mesocarp-specific expression. Gel mobility shift assay revealed a strong interaction of the leaf nuclear extract with the 21-bp region. An AGTTAGG core-sequence within this region was identified as a novel negative regulatory element controlling fruit-specificity of the MSP1 promoter. Abscisic acid (ABA) and copper (Cu(2+)) induced the activity of the promoter and its 5' deletions more effectively than methyl jasmonate (MeJa) and ethylene. In the mesocarp, the full length promoter showed stronger inducibility in response to ABA and Cu(2+) than its 5' deletions, while in leaves, the -420 nt fragment was the most inducible by ABA and Cu(2+). These results suggest that the MSP1 promoter and its regulatory regions are potentially useful for engineering fruit-specific and inducible gene expression in oil palm.
MAIN CONCLUSION: X-ray microtomography results revealed that delignification process damaged the oil palm fibers, which correlated well with reduction of lignin components and increase of the phenolic content. Biodegradation investigation of natural fibers normally focuses on physico-chemical analysis, with less emphasis on physical aspect like fiber structures affect from microbial activity. In this work, the performance of Pycnoporus sanguineus to delignify oil palm empty fruit bunch fibers through solid-state fermentation utilizing various ratio of POME sludge was reported. In addition to tensile testing, physico-chemical and X-ray microtomography (µ-CT) analyses on the oil palm fibers were conducted to determine the effectiveness of the degradation process. The best ratio of fiber to fungi (60:40) was chosen based on the highest lignin loss and total phenolic content values and further investigation was performed to obtain fermentation kinetics data of both laccase and manganese peroxidase. µ-CT results revealed that delignification process damaged the pre-treated and untreated fibers structure, as evident from volume reduction after degradation process. This is correlated with reduction of lignin component and increase of the phenolic content, as well as lower stress-strain curves of the pre-treated fibers compared to the untreated ones (from tensile testing). It is suggested that P. sanguineus preferred to consume the outer layer of the fiber, before it penetrates through the cellular structure of the inner fiber.
The diacylglycerol acyltransferases (DGAT) (diacylglycerol:acyl-CoA acyltransferase, EC 2.3.1.20) are a key group of enzymes that catalyse the final and usually the most important rate-limiting step of triacylglycerol biosynthesis in plants and other organisms. Genes encoding four distinct functional families of DGAT enzymes have been characterised in the genome of the African oil palm, Elaeis guineensis. The contrasting features of the various isoforms within the four families of DGAT genes, namely DGAT1, DGAT2, DGAT3 and WS/DGAT are presented both in the oil palm itself and, for comparative purposes, in 12 other oil crop or model/related plants, namely Arabidopsis thaliana, Brachypodium distachyon, Brassica napus, Elaeis oleifera, Glycine max, Gossypium hirsutum, Helianthus annuus, Musa acuminata, Oryza sativa, Phoenix dactylifera, Sorghum bicolor, and Zea mays. The oil palm genome contains respectively three, two, two and two distinctly expressed functional copies of the DGAT1, DGAT2, DGAT3 and WS/DGAT genes. Phylogenetic analyses of the four DGAT families showed that the E. guineensis genes tend to cluster with sequences from P. dactylifera and M. acuminata rather than with other members of the Commelinid monocots group, such as the Poales which include the major cereal crops such as rice and maize. Comparison of the predicted DGAT protein sequences with other animal and plant DGATs was consistent with the E. guineensis DGAT1 being ER located with its active site facing the lumen while DGAT2, although also ER located, had a predicted cytosol-facing active site. In contrast, DGAT3 and some (but not all) WS/DGAT in E. guineensis are predicted to be soluble, cytosolic enzymes. Evaluation of E. guineensis DGAT gene expression in different tissues and developmental stages suggests that the four DGAT groups have distinctive physiological roles and are particularly prominent in developmental processes relating to reproduction, such as flowering, and in fruit/seed formation especially in the mesocarp and endosperm tissues.
Dehydration-responsive element binding (DREB) transcription factor plays an important role in controlling the expression of abiotic stress responsive genes. An intronless oil palm EgDREB1 was isolated and confirmed to be a nuclear localized protein. Electrophoretic mobility shift and yeast one-hybrid assays validated its ability to interact with DRE/CRT motif. Its close evolutionary relation to the dicot NtDREB2 suggests a universal regulatory role. In order to determine its involvement in abiotic stress response, functional characterization was performed in oil palm seedlings subjected to different levels of drought severity and in EgDREB1 transgenic tomato seedlings treated by abiotic stresses. Its expression in roots and leaves was compared with several antioxidant genes using quantitative real-time PCR. Early accumulation of EgDREB1 in oil palm roots under mild drought suggests possible involvement in the initiation of signaling communication from root to shoot. Ectopic expression of EgDREB1 in T1 transgenic tomato seedlings enhanced expression of DRE/CRT and non-DRE/CRT containing genes, including tomato peroxidase (LePOD), ascorbate peroxidase (LeAPX), catalase (LeCAT), superoxide dismutase (LeSOD), glutathione reductase (LeGR), glutathione peroxidase (LeGP), heat shock protein 70 (LeHSP70), late embryogenesis abundant (LeLEA), metallothionine type 2 (LeMET2), delta 1-pyrroline-5- carboxylate synthetase (LePCS), ABA-aldehyde oxidase (LeAAO) and 9-cis- Epoxycarotenoid dioxygenase (LeECD) under PEG treatment and cold stress (4 °C). Altogether, these findings suggest that EgDREB1 is a functional regulator in enhancing tolerance to drought and cold stress.
Understanding the mechanism of interaction between the oil palm and its key pathogen, Ganoderma spp. is crucial as the disease caused by this fungal pathogen leads to a major loss of revenue in leading palm oil producing countries in Southeast Asia. Here in this study, we assess the morphological and biochemical changes in Ganoderma disease infected oil palm seedling roots in both resistant and susceptible progenies. Rubber woodblocks fully colonized by G. boninense were applied as a source of inoculum to artificially infect the roots of resistant and susceptible oil palm progenies. Gas chromatography-mass spectrometry was used to measure an array of plant metabolites in 100 resistant and susceptible oil palm seedling roots treated with pathogenic Ganoderma boninense fungus. Statistical effects, univariate and multivariate analyses were used to identify key-Ganoderma disease associated metabolic agitations in both resistant and susceptible oil palm root tissues. Ganoderma disease related defense shifts were characterized based on (i) increased antifungal activity in crude extracts, (ii) increased lipid levels, beta- and gamma-sitosterol particularly in the resistant progeny, (iii) detection of heterocyclic aromatic organic compounds, benzo [h] quinoline, pyridine, pyrimidine (iv) elevation in antioxidants, alpha- and beta-tocopherol (iv) degraded cortical cell wall layers, possibly resulting from fungal hydrolytic enzyme activity needed for initial penetration. The present study suggested that plant metabolites mainly lipids and heterocyclic aromatic organic metabolites could be potentially involved in early oil palm defense mechanism against G. boninense infection, which may also highlight biomarkers for disease detection, treatment, development of resistant variety and monitoring.
KEY MESSAGE: TAAAAT and a novel motif, GCTTCA found in the oil palm stearoyl-ACP desaturase (SAD1) promoter are involved in regulating mesocarp-specific expression. Two key fatty acid biosynthetic genes, stearoyl-ACP desaturase (SAD1), and acyl-carrier protein (ACP3) in Elaeis guineensis (oil palm) showed high level of expression during the period of oil synthesis in the mesocarp [12-19 weeks after anthesis (w.a.a.)] and kernel (12-15 w.a.a.). Both genes are expressed in spear leaves at much lower levels and the expression increased by 1.5-fold to 2.5-fold following treatments with ethylene and abscisic acid (ABA). Both SAD1 and ACP3 promoters contain phytohormone-responsive, light-responsive, abiotic factors/wounding-responsive, endosperm specificity and fruit maturation/ripening regulatory motifs. The activities of the full length and six 5' deletion fragments of the SAD1 promoter were analyzed in transiently transformed oil palm tissues by quantitative β-glucuronidase (GUS) fluorometric assay. The highest SAD1 promoter activity was observed in the mesocarp followed by kernel and the least in the leaves. GUS activity in the D3 deletion construct (- 486 to + 108) was the highest, while the D2 (- 535 to + 108) gave the lowest suggesting the presence of negative cis-acting regulatory element(s) in the deleted - 535 to - 486 (49 bp). It was found that the 49-bp region binds to the nuclear protein extract from mesocarp but not from leaves in electrophoretic mobility shift assay (EMSA). Further fine-tuned analysis of this 49-bp region using truncated DNA led to the identification of GCTTCA as a novel motif in the SAD1 promoter. Interestingly, another known fruit ripening-related motif, LECPLEACS2 (TAAAAT) was found to be required for effective binding of the novel motif to the mesocarp nuclear protein extract.