Dussert S, Tranbarger TJ, Joët T, Morcillo F (2012) Regulatory mechanisms underlying oil
palm mesocarp maturation and functional specialization in lipid and carotenoid metabolism.
20
thInternational Symposium on Plant lipids (ISPL 2012), 8-13 July, 2012, Seville, Spain
S4 P
Regulatory mechanisms underlying oil palm mesocarp maturation and functional specialization in
lipid and carotenoid metabolism
Dussert S*, Tranbarger TJ, Joët T, Morcillo F
UMR Diade, IRD and Cirad, Montpellier, France
*Corresponding Author:
stephane.dussert@ird.fr
The lipid‐rich fleshy mesocarp tissue of the oil palm (Elaeis guineensis) fruit is not only 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, 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.
Regulatory mechanisms underlying oil palm mesocarp maturation
and functional specialization in lipid and carotenoid metabolism
Stéphane Dussert, Timothy Tranbarger, Thierry Joët, Fabienne Morcillo IRD, UMR Diade, Montpellier, France
The monocotyledonous oil palm (Elaeis guineensis) fruit is a drupe whose thick fleshy mesocarp is exceptionally rich in oil (80% dry mass), making this species the highest oil-yielding crop in the world. The mesocarp is also especially abundant in carotenoids, and crude palm oil is the richest dietary source of provitamin A. Our objective was to provide a basis to understand the molecular regulation and coordination of TAG and carotenoid biosynthesis during oil palm mesocarp maturation and ripening compared with those found in seeds and non-oily fruit.
Introduction
Morphological, histological, and biochemical (hormones, lipids) analyses were used to define phases of oil palm fruit development, maturation, and ripening (Fig. 1)
Fruit development
Phase IV, between 120 and 140 DAP, is characterized by the onset of lipid and carotenoid accumulation
Very low amounts of all hormones examined, including auxin, GA and cytokinin, ABA, and ethylene, were detected during phase IV
Figure 1. Scheme representing the major events that occur during the
phases of mesocarp development.
Oil biosynthesis
This detailed morphological, histological and biochemical description of fruit development enabled to chose the stages for transcriptome 454 pyrosequencing
FA synthesis in the plastid and TAG assembly in the ER seem to be governed by two different transcriptional programs
A transcript encoding a transcription factor similar to WRINKLED1 Is highly expressed in the mesocarp during FA biosynthesis
The core FA synthetic machinery of the oil palm mesocarp is remarkably coordinated at the transcriptional level (Fig. 3)
Canonical AW elements were found in several transcripts encoding enzymes involved in glycolysis and FA synthesis
The transcription peak of FA biosynthetic genes coincided with the onset of oil accumulation
ethylene, were detected during phase IV
Oil accumulates within subcellular spherical organelles (10–15 µm in diameter, six to 12 per mesocarp cell) that occupy the whole volume of the cells (Fig. 2)
Mesocarp cells also contain distinct regions, presumably chromoplasts, with high carotenoid concentrations (Fig. 2)
Figure 2. Confocal microscopy of mesocarp oil (left) andβ-carotene (right)
104 CL1Contig7856* CL1Contig3878* 218 186 213 CL1Contig4893* CL1Contig320* CL1Contig402 57 CL1Contig1115* 796 CL1Contig7313* 214 ACC (CTα) ACC (CTβ) ACC (BC) MAT KAS III KAR HAD CL1Contig7926* 1620 EAR SAD CL1Contig4595* 194 742 CL1Contig8007* Acetyl-CoA Malonyl-CoA Malonyl-ACP 3-Ketoacyl-ACP 3-hydroxyacyl-ACP enoyl-ACP 4:0 to 16:0-ACP KAS I 18:1-ACP 18:0-ACP KAS II CL52Contig4* 78 15 CL1700Contig1 16:0-ACP 94 CL1Contig8939* 17 CL2305Contig1* FAT A&B CL1Contig3607* 103 LACS 1-Acylglycerol-3-Phosphate (LPA) GPAT Glycerol-3-Phosphate Plastid CL278Contig233 CL1Contig9059* 255 PK CL1Contig7194* 63 ENOp CL1Contig5371* 347 CL1Contig8373* 409 WRI1 Pyruvate PEP 2-PGA Between stage relative expression (%)
0 1-2525-5050-75 75-99100
33CL1Contig7976
KAS A&B
16:0-CoA, 18:0-CoA, 18:1, 18:X-CoA pool CL181Contig1* 47 CL181Contig2* 26 PDH 40 CL1Contig8273* 42 CL1Contig5777* 100
Figure 4. Carotenoid and ABA biosynthetic pathways
with related metabolites and transcripts present during mesocarp development
Figure 3. FA synthesis and TAG assembly in the oil palm mesocarp as
reconstructed from the 454 pyrosequencing transcriptome. Gene expression levels at 100, 120, 140, 160 DAP are indicated with colored bars. *=significant differential expression
transcriptional programs
The massive carotene accumulation precedes ABA biosynthesis (Fig. 4)
Chloroplasts and chromoplasts share a common repertoire of carotenogenesis regulators
Tranbarger TJ, Dussert S, Joët T, Argout X, Summo M, Champion A, Cros D, Omore A, Nouy B, Morcillo F. (2011). Regulatory mechanisms underlying oil palm fruit mesocarp maturation, ripening and functional specialization in lipid and carotenoid metabolism. Plant Physiology, 156: 564–584.
The last acylating step of TAG assembly may involve several complementary routes
Carotene biosynthesis
Phytoene synthase (PSY) an phytoene desaturase (PDS) are likely the key players for carotenoid accumulation Genes involved in the desaturation steps and carotenoid storage show a fine coordinated transcriptional activation
Downstream steps involved in the cyclization of lycopene toward carotenes and upstream isoprenoid synthesis appear to be poorly regulated at the transcriptional level
Endoplasmic reticulum 1-Acylglycerol-3-Phosphate (LPA) 1,2-Diacylglycerol-3-Phosphate (PA) LPAAT 1,2-Diacylglycerol (DAG) PAP CPT 32 CL207Contig1 39 CL1Contig1074 CL1Contig157 42 18:1-PC 18:3-PC 18:2-PC FAD2 FAD3 PC pool 3939 84 CL1Contig785* CL274Contig1* Triacylglycerols 27 CL1Contig5429 15 CL875Contig1 DGAT1 CL1451Contig2 12 PDAT CL212Contig1* 33 LPCAT Acyl-CoA LPC Acyl-CoA 8 CL1Contig9221 DGAT2 LPCAT 80 100120140160 DAP 0 20 40 60 80 L ip id s (% D M ) GGPP PSY Lycopene ββββ-carotene Zeaxanthin PTOX/PDS LCY-E CYP97A or HYD PTOX/ZDS Violaxanthin ZEP Neoxanthin NSY α αα α-carotene LCY-B Zeinoxanthin CYP97A or HYD Lutein Xanthoxin Z-ISO CRTISO LCY-B NCED (CCD) Abscisic aldehyde XO ABAO ABAGT ABA8ox
ABA-GE ABA PA/PDA
# # CYP97C GPPS FPS GGPPS C5 C15 C20 C40 80100120140160 0 20 40 60 80 100 80100120140160 0 100 200 300 80100120140160 0 5 10 15 80100120140160 0 5 10 15 80100120140160 0 100 200 300 400 α µ 801001 20140160 0 1 00 2 00 3 00 4 00 D e sa tu ra ti o n C ycl iz a ti o n H y d ro x y la ti o n U p st re a m s te p s A B A m e ta b o li sm R e g u la ti o n CL1Contig1067* 61 NSY CL1Contig3063 9 NSY CL1Contig7010* 99 PSY 145CL4Contig1* PDS CL1Contig2353* 49 PTOX CL1Contig3216 80 ZDS CL1069Contig1 15 Z-ISO CL1Contig3880* 68 XO CL3128Contig1 14 XO CL712Contig2 17 ABA8OX CL712Contig3 6 ABA8OX CL1Contig4536 70 CCD CL1Contig8851 32 CCD CL904Contig1 21 CYP97A CL3951Contig3 6 ZEP CL10427Contig1 3 HYD CL3273Contig1 13 Fibrillin CL1Contig9132 9 Fibrillin CL1Contig4160 76 Fibrillin CL4015Contig1 8 LCY-B CL10712Contig1 5 LCY-E CL13752Contig1 2 LCY-E CL730Contig2* 33 ABAGT CL2798Contig1 8 DET1 CL1452Contig1 14 DDB1A CL1341Contig1 14 14 OR CL162Contig1 41 SET CL1370Contig1 15 PHY-A CL1Contig1953 37 GPPS 37 CL1Contig8765* FPS CL1Contig4842 6 GGPPS CL1Contig3320 10 FPS CL6190Contig1 3 DXR CL1Contig2747 52 DXS CL6460Contig1 6 DXS
Days after Pollination 100 120 140 160 S to ra g e 80100120140160 0 20 40 60 80 100 CL10086Contig1 3 CRTISO DXS DXR CL4244Contig1 9 PHY-B CL3772Contig2 7 PHY-C CL5275Contig1* 14 PIF α -ca rote n e ( µ g.g -1) β -c aro te ne ( µ g.g -1 ) Lu te in ( µ g.g -1) Viola xa nth in ( µ g.g -1 ) A BAG E (ng.g -1) AB A (ng.g -1 ) PA & D PA (ng .g -1 )
