Oil palm (Elaeis guineensis Jacq.) is one of the most important oil bearing
crops in the world. However, genetic improvement of oil palm through
conventional breeding is extremely slow and costly, as the breeding cycle
can take up to 10 years. This has brought about interest in vegetative
propagation of oil palm. Since the introduction of oil palm tissue culture in
the 1970s, clonal propagation has proven to be useful in producing uniform
planting materials. However, despite considerable progress in improving the
tissue culture techniques, the callusing and embryogenesis rates from
proliferating callus cultures remain very low. Thus, understanding the gene
diversity and expression profiles during somatic embryogenesis is critical in
increasing the efficiency of these processes. To achieve this, a total of six
standard cDNA libraries, representing three developmental stages (nonembryogenic
callus, embryogenic callus and embryoids) in oil palm tissue culture, were generated in this study. Random sequencing of clones from
the embryogenic callus cDNA libraries generated 2,716 expressed sequence
tags (ESTs). These ESTs were combined with 14,883 ESTs available in
MPOB’s EST programme. The 17,599 ESTs were analysed, annotated and
assembled to generate 9,584 putative unigenes distributed in 3,268
consensi and 6,316 singletons. These unigenes were assigned putative
functions based on similarity and gene ontology annotations. A subset of
these ESTs were selected and spotted on cDNA microarrays. Both the EST
and microarray data analysis were able to identify expression profiles that
could differentiate non-embryogenic callus from embryogenic samples. The
in silico EST data analysis identified 52 unigenes that showed potential to be
developed as candidate markers for embryogenesis. The microarray
experiment identified 76 unigenes that could differentiate non-embryogenic
callus from embryogenic callus, embryoids and shoots from polyembyoids.
The EST and microarray data analysis revealed that lipid transfer proteins
were highly expressed in embryogenic tissues. The results also showed that
glutathione S-transferases were highly expressed in non-embryogenic
callus. This study has provided an overview of genes expressed during oil
palm tissue culture and real-time PCR analysis identified four genes
(pOP-EA00703, pOP-EA01249, pOP-EA01117, pOP-SFB01045) that had
the potential to be developed as molecular markers for embryogenesis
