BACKGROUND
sesame  belonging to the family pedaliaceae  <cit>  is one of the most ancient self-pollinated oilseed crops.
sesame is one of oilseed crops with the highest oil content of up to  <dig> %  in seeds of sesame cultivars and accessions  <cit>  when seed oil contents of other major oil crops peanut , oilseed rape  and soybean  contain up to  <dig> %   <cit> , up to 46%   <cit>  and up to  <dig> %   <cit> , respectively.
although recent intensive selection  aided with high throughput near-infrared spectroscopy for seed oil content determination with no seed damage can lead to more than 50% in oilseed rape, it is still lower than that having existed in sesame accessions for long time.
furthermore, sesame seed is highly nutritive in protein contents of the seed dry weight  and has distinctive flavor.
sesame oil has excellent stability due to the existence of the natural antioxidants such as lignans sesamin, sesamol, sesamolin and sesaminol produced during seed development  <cit> .
these natural antioxidants help to improve health qualities such as inhibiting Δ5-desaturase in mammals, enhancing vitamin e bioactivity, and inhibiting proliferation of human cancer cells  <cit> .
sesame lignans may also play a role in sesame resistance to insect pests and microbial pathogens  <cit> .
the study on synthesis of high oil content and these antioxidants is poor, partly because of poor dna and rna sequence resources.
at present, there are only about  <dig>  sesame est sequences available in genbank  <cit> .
lack of sequence information and poor understanding of related synthetic biology have hindered genetic improvement on these economic characters as well as high unsaturated fatty acids contents in sesame.
thereby, our objective in this study was to build a large set of est collection from developing seeds of sesame.
after construction of a normalized full-length cdna library, we carried out large scale sequencing of the library and obtained more than  <dig>  ests from developing seeds of high oil content chinese sesame cultivar zhongzhi  <dig>  and further performed bioinformatics analysis on the ests with focus on those involved in oil and lignin biosynthesis.
these sequence information will serve as the public-accessible fundamental resources for generation of molecular markers, genome annotation, gene discovery in sesame and comparative genomics study on oil contents of major oilseed crops.
RESULTS
est generation
to understand accumulation of oil and lignan, and determine time of sampling developing seeds for est sequencing, two sesame  cultivars zhongzhi  <dig> with high oil content and its contrast miaoqian with low oil content and early maturation were analyzed for accumulation of oil, fatty acids and lignans.
the results indicated that the two cultivars have different oil contents but similar profiles of fatty acid compositions .
both cultivars started quick increase in oil contents from  <dig> days after pollination to maturation and oil accumulation reached their peak at about  <dig> days.
therefore sampling time was determined as  <dig>   <dig> and  <dig> days after pollination.
considering annual productivity  and oil content of seeds, zhongzhi  <dig> was selected for construction of cdna library enriched in full-length coding sequences  <cit>  and est sequencing.
the primary titer of the cdna library was  <dig> ×  <dig> cfu/ml with more than 90% recombinant clones revealed by x-gal/iptg screening and a small-scale quality assessment was performed prior to commencement of large-scale sequencing  <cit> .
plasmid dnas were automatically prepared from the cdna clones and sequenced from the 5' end by the sanger method.
in total,  <dig>  ests from single-pass 5' sequencing of  <dig>  cdna clones passed the quality control for high confidence base call with an average read length of approximately  <dig> bp .
the overall sequencing success rate was 91%.
the est sequences generated in this study were deposited in genbank with the accession numbers jk045130-jk <dig>  the gc content of the est sequences was approximately  <dig> %.
approximately  <dig> % of the  <dig>  sequences appeared twice or more times.
clustering of ests
after screening of low-quality dna and trimming of vector sequences, phrap program  <cit>  was used to cluster the est sequences and produce a uniests data set which comprised  <dig>  tentative unique contigs  and  <dig>  tentative unique singletons sequences .
the number of ests in the tucs ranged from  <dig> to  <dig> and there are more than  <dig> % contigs with  <dig> ests,  <dig> % with  <dig> ests and  <dig> % with 4- <dig> ests.
among these uniests sequences,  <dig> % had significant matches to sequences in the non-redundant protein database  with an e value cut-off equal or less than 10- <dig>  comparison of our uniests data set with the sesame est sequence in genbank using blastn demonstrated that only  <dig> uniests  in our data set had significant matches to  <dig> sesame ests in genbank  .
comparison of the sesame uniests against the a. thaliana proteome database using blastx indicated 40% of these uniests with significant matches to those from a. thaliana .
based on identification of clusters of orthologous groups of protein   <cit>  ,  <dig>  uniests  of sesame seeds were assigned to cogs by blastx.
the proportion pattern of each cog subcategory was similar between sesame and a. thaliana seeds  <cit>  .
in these two sets of cdna sequences, only  <dig>  sesame uniests are matched to a. thaliana seed genes   <cit>  and 20% of these genes were involved in translation, ribosomal proteins synthesis, and 17% in posttranslational modification, protein turnover, chaperones.
only 1% of these genes were related to lipid transport and metabolism category.
protein coding regions
the full-length open reading frames  in the uniests data set were identified.
homology search of the  <dig>  uniests using blastx identified uniests with relatively high similarity  to known genes, where the sesame sequences, each had a start codon at a position similar to the protein sequence in genbank, form a data set of putative full-length orfs .
furthermore, the codon usage table  for the full-length sesame orfs was generated using codonw.
the sesame  codon usage table containing  <dig>  codons showed the gc content of the predicted coding region  and the gc frequency at the third position .
the analysis was the first version of sesame codon usage table which was not presented in the kazusa codon usage database http://www.kazusa.or.jp/codon/.
codon usage was calculated from  <dig> orfs containing  <dig>  codons.
gene ontology annotation
a total of  <dig>  uniests were successfully annotated with gene ontology  terms using blast2go program  <cit> .
an additional  <dig>  sequences were then annotated using interproscan program  <cit> .
overall, a total of  <dig>  uniests were annotated with  <dig>  go terms distributing among the three main go categories.
<dig>  tentative unique genes  representing  <dig>  uniests across the various go terms were examined with wego  <cit>  .
under the category biological process, subcategories "cellular process" and "metabolic process" accounted for approximately  <dig> % and  <dig> % of the annotations for the tugs, respectively, reflecting activeness of these processes.
there are an overlap which is largely represented by the cellular metabolic process  in the two subcategories and in the subcategory "metabolic process," primary metabolic process , macromolecule metabolic process  and biosynthesis  account for large proportions, suggesting active metabolism of storage substances such as oil, lignan and proteins.
in correspondence to these processes, in the main category molecular function,  <dig> % of the tugs annotations were grouped into the subcategory "binding" and  <dig> % in the subcategory "catalytic activity" .
analysis of ests involved in oil biosynthesis in developing sesame seeds
comparative analysis indicated that the most redundant genes related to biosynthesis of fatty acid and oil in sesame included ketoacyl-coa thiolase , pyruvate dehydrogenase complex , plastidial long-chain acyl-coa synthetase , stearoyl-acp desaturase , acetyl-coa carboxylase , ketoacyl-coa reductase , oil-body oleosin , diacylglycerol acyltransferase  etc.
<dig> uniests candidates were homologous to arabidopsis oil-related genes   <cit> .
of these,  <dig> uniests were mapped to the sesame genome sequence  and just  <dig> genes like pdhc, obo and lacs are homologous to those in the public sesame ests database .
in the "fatty acid synthesis in the plastids pathway"  <cit> , most of the key enzymes were found in our data set, such as the pdhc, acc, plastidial acyl carrier protein  and kar, except an important enzymes malonyl-coa: acp malonyltransferase .
after blasting against the whole sesame genome assembly, we found that most of these genes had lower copy numbers than those in arabidopsis, except one gene encoding beta-ketoacyl-acp synthase i  which have  <dig> copies whereas the genomes of arabidopsis has  <dig> copy .
kas i catalyzes the elongation of fatty acid synthesis for the carbon chain from c <dig> to c <dig>  and played a crucial role in chloroplast division and embryo development  <cit> .
the main components of sesame seed oil, oleic acid and linoleic acid, continuously increased up to about 80% of total fatty acids in the mature seeds .
some uniests related to these fatty acids elongation and desaturation in sesame were first reported in this study, such as putative full-length uniests encoding ketoacyl-acp synthase ii  sad and endoplasmic reticulum  oleate desaturase  which played important roles in the process of the conversion of 16:0-18: <dig> and desaturation.
triacylglycerol  biosynthesis occurs at the er and probably involves in reactions in the oil body as well  <cit> .
only four major genes, dgat <dig>  phosphatidylcholine: diacylglycerol acyltransferase , obo and caleosin, were detected, which involved in the last step of the tag synthesis reaction and oil body formation in the pathway of synthesis and storage of oil.
dgat <dig> and pdat have been known as the very important genes greatly affecting oil body formation and oil content  <cit> .
obo and caleosin were believed to facilitate mobilization of the tag storage reserves  <cit> .
of  <dig>  annotated uniests with putative transcription factor activity,  <dig> uniests were identified involved in oil accumulation, and they are homologous to a. thaliana transcription factor  leafy cotyledon <dig> , pickle  and wrinkled <dig> , respectively, suggesting their conservation and importance in transcriptional regulation of the fatty acid biosynthetic pathway.
of these tfs, putative sesame lec <dig>  and siwri <dig>  like those in arabidopsis, are single copies after blasting against whole sesame genome assembly  and the sequence similarity of the two genes are 47% and 43% between sesame and arabidopsis, respectively .
atlec <dig> positively regulates atwri <dig> and a large repertoire of fatty acid synthetic genes and several glycolytic genes  <cit> .
overexpression of atwri <dig> in arabidopsis increased tag content in transgenic plants  <cit>  and overexpression of atlec <dig> and its orthologs in canola  caused an increased fatty acid level in transgenic plants  <cit> .
these homologs identified in sesame may have similar functions in oil biosynthesis.
analysis of ests involved in lignan biosynthesis in developing sesame seeds
two major oil-soluble lignans, sesamin and sesamolin  <cit>  were quantitatively determined in the seeds of two cultivars  with contrast oil contents.
total lignan  content was detectable  <dig> days after pollination and continuously accumulated until seed maturation .
interestingly sesamin content continuously increased from  <dig> days after pollination to seed maturation while sesamolin increased to its highest level at  <dig> days after pollination, and sesamin content was almost as twice as that of sesamolin at  <dig> days after pollination .
in these two cultivars, it is clear that lignan formation was developmentally regulated  <cit> --lignan accumulation and seed development  keep the same pace.
with seed development, the conversion ratio into sesamolin decreased whereas sesamin accumulation increased .
the antioxidant lignans, sesamin and sesamolin, are biosynthesized via the phenylpropanoid biosynthesis pathway  <cit> .
in the pathway, tyrosine or phenylalanine is first converted into coniferyl alcohol which then undergoes stereoselective coupling to give pinoresinol, and further pinoresinol is metabolized in maturing seeds to piperitol, sesamin and sesamolin which are catalysed by o2/nadph cytochrome p450s in the reactions  <dig>   <dig>  and  <dig> where methylenedioxy bridges are formed   <cit> .
one hundred and  <dig> ests, corresponding to  <dig> ec numbers  , were identified possibly involved in the biosynthesis of sesame lignans during seed development according to kegg blast result.
compared to the arabidopsis database,  <dig> ests were homologous to  <dig> genes of arabidopsis.
in the genbank database, there are just  <dig> sesame ests homologous to  <dig> uniests of our dataset encoding three enzyme genes .
most of the est candidates corresponding to enzymatic reactions in the biosynthetic pathway of sesame lignans, such as trans-cinnamate 4-monooxygenase , oxidoreductases, comt, 4-coumarate--coa ligase , cinnamoyl-coa reductase , cad etc., were first identified from sesame .
the gene 4cl has the most abundant ests .
there are  <dig> copies of the gene encoding comt in the sesame genome , but this gene is absent in the genomes of arabidopsis and soybean.
surprisingly, neither phenylalanine ammonia-lyase nor tyrosine ammonia-lyase encoded ests were detected in the sesame seed ests.
thirty five ests of putative nadph-cytochrome p <dig> oxidoreductase were identified, which involve in the important steps of sesame lignan production, including a gene encoding cyp81q <dig> known for dual methylendioxy bridge formation on pinoresinol to produce sesamin via piperitol  <cit> .
because little information is available about enzymes for reactions from sesamin to sesamolin and from piperitol to sesamolinol  <cit> , ests responsible for these enzymes was not able to be identified.
est-derived simple sequence repeat  markers
simple-sequence repeats  have become one of major markers for population genetic analyses and marker-aided breeding  <cit> .
a shortage of sesame molecular markers especially the est-derived ssrs  have limited the efficiency of sesame molecular breeding  <cit> .
hence development of a large collection of est-ssr will be very important source.
in total,  <dig>  uniests containing  <dig>  non-redundant  ssrs were identified from  <dig>  uniests.
the uniests represented about  <dig>  mb of genic sequences.
a total of  <dig> sequences contain more than one ssr.
the est-derived nr ssrs were represented by mono-, di-, tri-, tetra- and pentanucleotide repeat motifs.
this corresponds to an overall ssr density of approximately one ssr per  <dig>  kb or one ssr-containing sequence in  <dig> % of the nr est sequences.
about  <dig> % of the ssrs identified were compound ssrs, which were defined as two neighbouring repeats located less than  <dig> nucleotides apart in a single sequence.
the frequencies of the ssr motifs identified from  <dig>  uniests were summarized in table  <dig>  based on the distribution of ssr motifs, ag/ct motifs represented the most abundant dinucleotide repeat motifs .
the most common trinucleotide repeat motifs are, aag/ctt  and the most abundant tetranucleotide repeat motifs are the aagt/attc  .
non-redundant ssr motifs were derived from  <dig>  uniests.
CONCLUSIONS
this study provided a set of ests enriched in full-length coding sequence generated from developing seeds.
the number of these ests is more than  <dig>  fold of the total number of entries for sesame in genbank.
from this set of ests,  <dig>  putative functional genes from developing seeds were identified, accounting for one third of total genes in the genome.
most of the transcripts are the first representatives from sesame seeds.
most key enzymes and regulatory factors involved in fatty acid metabolism were found in our data, especially the enzymes responsible for the main unsaturated fatty acid synthesis, tag synthesis reactions and oil body formation.
some conservative tfs significantly regulating oil synthesis were also identified.
these provide a foundation for future comparative analysis of oil biosynthesis of different oilseeds.
the uniests associated with biosynthetic enzymes of sesame lignans, sesamin and sesamolin, were identified and this information will be helpful for further studies on sesame lignan production.
this large number of ests, half of them with full-length, have been used for sesame genome annotation in our sesame genome sequencing project and will be useful resource for the functional gene analysis and molecular marker development of traits such as contents of oil, fatty acids and lignan in sesame and for comparative genomics study of seed oil biosynthesis in different oilseed plants.

 sesame belonging to the family pedaliaceae is one of the most ancient self-pollinated oilseed crops. sesame is one of oilseed crops with the highest oil content of up to % in seeds of sesame cultivars and accessions when seed oil contents of other major oil crops peanut, oilseed rape and soybean contain up to %, up to 46% and up to %, respectively. although recent intensive selection aided with high throughput near-infrared spectroscopy for seed oil content determination with no seed damage can lead to more than 50% in oilseed rape, it is still lower than that having existed in sesame accessions for long time. furthermore, sesame seed is highly nutritive in protein contents of the seed dry weight and has distinctive flavor. sesame oil has excellent stability due to the existence of the natural antioxidants such as lignans sesamin, sesamol, sesamolin and sesaminol produced during seed development. these natural antioxidants help to improve health qualities such as inhibiting Δ5-desaturase in mammals, enhancing vitamin e bioactivity, and inhibiting proliferation of human cancer cells. sesame lignans may also play a role in sesame resistance to insect pests and microbial pathogens. the study on synthesis of high oil content and these antioxidants is poor, partly because of poor dna and rna sequence resources. at present, there are only about sesame est sequences available in genbank. lack of sequence information and poor understanding of related synthetic biology have hindered genetic improvement on these economic characters as well as high unsaturated fatty acids contents in sesame. thereby, our objective in this study was to build a large set of est collection from developing seeds of sesame. after construction of a normalized full-length cdna library, we carried out large scale sequencing of the library and obtained more than ests from developing seeds of high oil content chinese sesame cultivar zhongzhi and further performed bioinformatics analysis on the ests with focus on those involved in oil and lignin biosynthesis. these sequence information will serve as the public-accessible fundamental resources for generation of molecular markers, genome annotation, gene discovery in sesame and comparative genomics study on oil contents of major oilseed crops.  est generation to understand accumulation of oil and lignan, and determine time of sampling developing seeds for est sequencing, two sesame cultivars zhongzhi with high oil content and its contrast miaoqian with low oil content and early maturation were analyzed for accumulation of oil, fatty acids and lignans. the results indicated that the two cultivars have different oil contents but similar profiles of fatty acid compositions. both cultivars started quick increase in oil contents from days after pollination to maturation and oil accumulation reached their peak at about days. therefore sampling time was determined as and days after pollination. considering annual productivity and oil content of seeds, zhongzhi was selected for construction of cdna library enriched in full-length coding sequences and est sequencing. the primary titer of the cdna library was × cfu/ml with more than 90% recombinant clones revealed by x-gal/iptg screening and a small-scale quality assessment was performed prior to commencement of large-scale sequencing. plasmid dnas were automatically prepared from the cdna clones and sequenced from the 5' end by the sanger method. in total, ests from single-pass 5' sequencing of cdna clones passed the quality control for high confidence base call with an average read length of approximately bp. the overall sequencing success rate was 91%. the est sequences generated in this study were deposited in genbank with the accession numbers jk045130-jk the gc content of the est sequences was approximately %. approximately % of the sequences appeared twice or more times. clustering of ests after screening of low-quality dna and trimming of vector sequences, phrap program was used to cluster the est sequences and produce a uniests data set which comprised tentative unique contigs and tentative unique singletons sequences. the number of ests in the tucs ranged from to and there are more than % contigs with ests, % with ests and % with 4- ests. among these uniests sequences, % had significant matches to sequences in the non-redundant protein database with an e value cut-off equal or less than 10- comparison of our uniests data set with the sesame est sequence in genbank using blastn demonstrated that only uniests in our data set had significant matches to sesame ests in genbank. comparison of the sesame uniests against the a. thaliana proteome database using blastx indicated 40% of these uniests with significant matches to those from a. thaliana. based on identification of clusters of orthologous groups of protein, uniests of sesame seeds were assigned to cogs by blastx. the proportion pattern of each cog subcategory was similar between sesame and a. thaliana seeds. in these two sets of cdna sequences, only sesame uniests are matched to a. thaliana seed genes and 20% of these genes were involved in translation, ribosomal proteins synthesis, and 17% in posttranslational modification, protein turnover, chaperones. only 1% of these genes were related to lipid transport and metabolism category. protein coding regions the full-length open reading frames in the uniests data set were identified. homology search of the uniests using blastx identified uniests with relatively high similarity to known genes, where the sesame sequences, each had a start codon at a position similar to the protein sequence in genbank, form a data set of putative full-length orfs. furthermore, the codon usage table for the full-length sesame orfs was generated using codonw. the sesame codon usage table containing codons showed the gc content of the predicted coding region and the gc frequency at the third position. the analysis was the first version of sesame codon usage table which was not presented in the kazusa codon usage database http://www.kazusa.or.jp/codon/. codon usage was calculated from orfs containing codons. gene ontology annotation a total of uniests were successfully annotated with gene ontology terms using blast2go program. an additional sequences were then annotated using interproscan program. overall, a total of uniests were annotated with go terms distributing among the three main go categories. tentative unique genes representing uniests across the various go terms were examined with wego. under the category biological process, subcategories "cellular process" and "metabolic process" accounted for approximately % and % of the annotations for the tugs, respectively, reflecting activeness of these processes. there are an overlap which is largely represented by the cellular metabolic process in the two subcategories and in the subcategory "metabolic process," primary metabolic process, macromolecule metabolic process and biosynthesis account for large proportions, suggesting active metabolism of storage substances such as oil, lignan and proteins. in correspondence to these processes, in the main category molecular function, % of the tugs annotations were grouped into the subcategory "binding" and % in the subcategory "catalytic activity". analysis of ests involved in oil biosynthesis in developing sesame seeds comparative analysis indicated that the most redundant genes related to biosynthesis of fatty acid and oil in sesame included ketoacyl-coa thiolase, pyruvate dehydrogenase complex, plastidial long-chain acyl-coa synthetase, stearoyl-acp desaturase, acetyl-coa carboxylase, ketoacyl-coa reductase, oil-body oleosin, diacylglycerol acyltransferase etc. uniests candidates were homologous to arabidopsis oil-related genes. of these, uniests were mapped to the sesame genome sequence and just genes like pdhc, obo and lacs are homologous to those in the public sesame ests database. in the "fatty acid synthesis in the plastids pathway", most of the key enzymes were found in our data set, such as the pdhc, acc, plastidial acyl carrier protein and kar, except an important enzymes malonyl-coa: acp malonyltransferase. after blasting against the whole sesame genome assembly, we found that most of these genes had lower copy numbers than those in arabidopsis, except one gene encoding beta-ketoacyl-acp synthase i which have copies whereas the genomes of arabidopsis has copy. kas i catalyzes the elongation of fatty acid synthesis for the carbon chain from c to c and played a crucial role in chloroplast division and embryo development. the main components of sesame seed oil, oleic acid and linoleic acid, continuously increased up to about 80% of total fatty acids in the mature seeds. some uniests related to these fatty acids elongation and desaturation in sesame were first reported in this study, such as putative full-length uniests encoding ketoacyl-acp synthase ii sad and endoplasmic reticulum oleate desaturase which played important roles in the process of the conversion of 16:0-18: and desaturation. triacylglycerol biosynthesis occurs at the er and probably involves in reactions in the oil body as well. only four major genes, dgat phosphatidylcholine: diacylglycerol acyltransferase, obo and caleosin, were detected, which involved in the last step of the tag synthesis reaction and oil body formation in the pathway of synthesis and storage of oil. dgat and pdat have been known as the very important genes greatly affecting oil body formation and oil content. obo and caleosin were believed to facilitate mobilization of the tag storage reserves. of annotated uniests with putative transcription factor activity, uniests were identified involved in oil accumulation, and they are homologous to a. thaliana transcription factor leafy cotyledon, pickle and wrinkled, respectively, suggesting their conservation and importance in transcriptional regulation of the fatty acid biosynthetic pathway. of these tfs, putative sesame lec and siwri like those in arabidopsis, are single copies after blasting against whole sesame genome assembly and the sequence similarity of the two genes are 47% and 43% between sesame and arabidopsis, respectively. atlec positively regulates atwri and a large repertoire of fatty acid synthetic genes and several glycolytic genes. overexpression of atwri in arabidopsis increased tag content in transgenic plants and overexpression of atlec and its orthologs in canola caused an increased fatty acid level in transgenic plants. these homologs identified in sesame may have similar functions in oil biosynthesis. analysis of ests involved in lignan biosynthesis in developing sesame seeds two major oil-soluble lignans, sesamin and sesamolin were quantitatively determined in the seeds of two cultivars with contrast oil contents. total lignan content was detectable days after pollination and continuously accumulated until seed maturation. interestingly sesamin content continuously increased from days after pollination to seed maturation while sesamolin increased to its highest level at days after pollination, and sesamin content was almost as twice as that of sesamolin at days after pollination. in these two cultivars, it is clear that lignan formation was developmentally regulated --lignan accumulation and seed development keep the same pace. with seed development, the conversion ratio into sesamolin decreased whereas sesamin accumulation increased. the antioxidant lignans, sesamin and sesamolin, are biosynthesized via the phenylpropanoid biosynthesis pathway. in the pathway, tyrosine or phenylalanine is first converted into coniferyl alcohol which then undergoes stereoselective coupling to give pinoresinol, and further pinoresinol is metabolized in maturing seeds to piperitol, sesamin and sesamolin which are catalysed by o2/nadph cytochrome p450s in the reactions and where methylenedioxy bridges are formed. one hundred and ests, corresponding to ec numbers, were identified possibly involved in the biosynthesis of sesame lignans during seed development according to kegg blast result. compared to the arabidopsis database, ests were homologous to genes of arabidopsis. in the genbank database, there are just sesame ests homologous to uniests of our dataset encoding three enzyme genes. most of the est candidates corresponding to enzymatic reactions in the biosynthetic pathway of sesame lignans, such as trans-cinnamate 4-monooxygenase, oxidoreductases, comt, 4-coumarate--coa ligase, cinnamoyl-coa reductase, cad etc., were first identified from sesame. the gene 4cl has the most abundant ests. there are copies of the gene encoding comt in the sesame genome, but this gene is absent in the genomes of arabidopsis and soybean. surprisingly, neither phenylalanine ammonia-lyase nor tyrosine ammonia-lyase encoded ests were detected in the sesame seed ests. thirty five ests of putative nadph-cytochrome p oxidoreductase were identified, which involve in the important steps of sesame lignan production, including a gene encoding cyp81q known for dual methylendioxy bridge formation on pinoresinol to produce sesamin via piperitol. because little information is available about enzymes for reactions from sesamin to sesamolin and from piperitol to sesamolinol, ests responsible for these enzymes was not able to be identified. est-derived simple sequence repeat markers simple-sequence repeats have become one of major markers for population genetic analyses and marker-aided breeding. a shortage of sesame molecular markers especially the est-derived ssrs have limited the efficiency of sesame molecular breeding. hence development of a large collection of est-ssr will be very important source. in total, uniests containing non-redundant ssrs were identified from uniests. the uniests represented about mb of genic sequences. a total of sequences contain more than one ssr. the est-derived nr ssrs were represented by mono-, di-, tri-, tetra- and pentanucleotide repeat motifs. this corresponds to an overall ssr density of approximately one ssr per kb or one ssr-containing sequence in % of the nr est sequences. about % of the ssrs identified were compound ssrs, which were defined as two neighbouring repeats located less than nucleotides apart in a single sequence. the frequencies of the ssr motifs identified from uniests were summarized in table based on the distribution of ssr motifs, ag/ct motifs represented the most abundant dinucleotide repeat motifs. the most common trinucleotide repeat motifs are, aag/ctt and the most abundant tetranucleotide repeat motifs are the aagt/attc. non-redundant ssr motifs were derived from uniests.  this study provided a set of ests enriched in full-length coding sequence generated from developing seeds. the number of these ests is more than fold of the total number of entries for sesame in genbank. from this set of ests, putative functional genes from developing seeds were identified, accounting for one third of total genes in the genome. most of the transcripts are the first representatives from sesame seeds. most key enzymes and regulatory factors involved in fatty acid metabolism were found in our data, especially the enzymes responsible for the main unsaturated fatty acid synthesis, tag synthesis reactions and oil body formation. some conservative tfs significantly regulating oil synthesis were also identified. these provide a foundation for future comparative analysis of oil biosynthesis of different oilseeds. the uniests associated with biosynthetic enzymes of sesame lignans, sesamin and sesamolin, were identified and this information will be helpful for further studies on sesame lignan production. this large number of ests, half of them with full-length, have been used for sesame genome annotation in our sesame genome sequencing project and will be useful resource for the functional gene analysis and molecular marker development of traits such as contents of oil, fatty acids and lignan in sesame and for comparative genomics study of seed oil biosynthesis in different oilseed plants. 
a normalized and full-length enriched cdna library from ~ days old immature seeds was constructed and randomly sequenced, leading to generation of expressed sequence tags which then formed contigs and singletons with % uniests being putative full-length open reading frames. in this study, we carried out a large scale of expressed sequence tags sequencing from developing sesame seeds and further conducted analysis on seed storage products-related genes. homologous genes involved in oil biosynthesis were identified including some conservative transcription factors regulating oil biosynthesis such as leafy cotyledon, pickle, wrinkled and majority of them were found for the first time in sesame seeds. however, genetic improvement efforts in sesame could not get benefit from molecular biology technology due to poor dna and rna sequence resources. one hundred and ests were identified possibly involved in biosynthesis of sesame lignans, sesamin and sesamolin. in total, putative functional genes from developing seeds were identified, which accounts for one third of total genes in the sesame genome. approximately of all these uniests have significant matches to the counterparts in nr database of genbank, and of them were assigned to one or more gene ontology terms. these est sequences enriched with full length will contribute to comparative genomic studies on sesame and other oilseed plants and serve as an abundant information platform for functional marker development and functional gene study.
 sesame is one of the most important oilseed crops with high oil contents and rich nutrient value. however, genetic improvement efforts in sesame could not get benefit from molecular biology technology due to poor dna and rna sequence resources. in this study, we carried out a large scale of expressed sequence tags sequencing from developing sesame seeds and further conducted analysis on seed storage products-related genes.  a normalized and full-length enriched cdna library from ~ days old immature seeds was constructed and randomly sequenced, leading to generation of expressed sequence tags which then formed contigs and singletons with % uniests being putative full-length open reading frames. approximately of all these uniests have significant matches to the counterparts in nr database of genbank, and of them were assigned to one or more gene ontology terms. homologous genes involved in oil biosynthesis were identified including some conservative transcription factors regulating oil biosynthesis such as leafy cotyledon, pickle, wrinkled and majority of them were found for the first time in sesame seeds. one hundred and ests were identified possibly involved in biosynthesis of sesame lignans, sesamin and sesamolin. in total, putative functional genes from developing seeds were identified, which accounts for one third of total genes in the sesame genome. further analysis of the uniests identified non-redundant simple sequence repeats.  this study has provided an overview of genes expressed during sesame seed development. this collection of sesame full-length cdnas covered a wide variety of genes in seeds, in particular, candidate genes involved in biosynthesis of sesame oils and lignans. these est sequences enriched with full length will contribute to comparative genomic studies on sesame and other oilseed plants and serve as an abundant information platform for functional marker development and functional gene study. 