Latepost exponential growth Stress related genes were over represented at all stages, but considerably more so at 12 16 dpp than at the younger ages of 04 and 8 dpp. The 1216 dpp age group had the highest rep resentation of abiotic and biotic stress related genes, in cluding a variety of heat shock, redox, biotic defense and ethylene related transcripts. Of the 120 genes in this group, 44 have high homology with genes associated with plant stress, including at least 13 transcription stress related factors such as WRKY70 ac tivator of SA dependent defense. radical induced cell death. ethylene response, salt stress, and heat shock tran scription factors. Overall, the group of genes with peak abundance at 12 16 dpp was significantly enriched for transcription fac tor genes accounting for 16% of the top 2.
5% set. This may be con trasted with the total cucumber fruit transcriptome data set where transcription and transcription factor activity related genes were represented at a normalized frequency of 0. 94 relative to occurrence in the Arabidopsis genome. Transcription factors in the top 2. 5% of 04 and 8 dpp groups also were represented at a comparable frequency to the Arabidopsis genome, selleck inhibitor accounting for 3. 7% and 4. 6% of the gene list, respectively. In addition to the stress related transcription factors with specific representation at 1216 dpp, several puta tive transcription factor homologs were annotated to be associated with development. Clas sically, fleshy fruit development is described to consist of three stages post pollination cell division, cell expan sion, and ripening.
These results suggest that the interval between expansive growth and ripening may in clude further developmental differentiation. selleckchem an emphasis on defense would be consistent with the role of fruit in protecting the developing seeds during embryo matur ation prior to facilitating seed dispersal. Finally, approximately 5% of the contigs represented by 30 reads either did not have identified putative homologs, or did not have homologs outside of cucurbits suggesting potentially unique genes specific to cucumber or cucur bits. The observation that these genes, as well as genes with homologs but with no annotated function, rarely oc curred in the 04 dpp group, suggests commonality among processes associated with early fruit set and cell division andor greater knowledge about the fruit set stage. The predominance of transcripts without non cucurbit homologs or with unknown predicted functions during the peak exponential growth stage may reflect fewer stud ies to date about this phase of growth, or unique adapta tions of cucurbits to allow for extreme fruit growth rates associated with these species.