ogical level. However a consistent genetic and genomic analysis of processes affecting pollen viability is currently non existent. The pollen development in Prunus species and other woody perennial plants from temperate climates such as apple and poplar is affected by the seasonal cessation of meristem growth termed endodormancy. Endodormancy contributes to elude the detrimental effects of the low temperatures in winter by preventing the resumption of growth under non optimal conditions for survival. The growth inhibition of endodormant buds is due to internal signals within the buds, in contrast to growth inhibition by other distal organs, or by environmen tal factors. For the purpose of this work we have employed the term dormancy to refer to the endodormant state.
In these species, the flower buds start to differentiate in summer and continue their reproductive development until growth is arrested in autumn. After a period of chilling accumulation required for dormancy release, pollen mother cells within Brefeldin_A the anthers initiate meiosis and further microspore development, resulting in fully mature pollen grains. In order to identify putative genes involved in tapetum function, pollen development and pollen wall formation in peach, we analyzed the results of two transcriptomic experiments comparing gene expression between dormant and dormancy released flower buds, and in peach cultivars with dif ferent dormancy behaviour. This work led us to postulate a role for several genes in sporopollenin synthesis and deposition, and transcriptional regulation of pollen development processes, based on expression analysis and previous works in model species.
Results and discussion Identification of genes up regulated in late stages of reproductive bud development Meristems of woody perennials from temperate climates go through the cold season in a dormant stage, pro tected into specialized structures named buds. In peach, reproductive buds are typically arranged in pairs, flanking a single vegetative bud. In suc cessive steps, flower buds are induced and differentiate in summer, and enter a dormancy period in autumn winter. The dormancy is released after a required chil ling period, whose length is genotype specific. Finally their reproductive organs resume growth and develop ment leading to blooming when temperature conditions become favourable.
In anthers, the release of dormancy initiates microsporogenesis, pollen develop ment and maturation. We previously studied the genome wide modification of gene expression in flower buds of peach through two complementary transcriptomic approaches. In the first work we isolated differentially enriched transcripts in dormant buds and dormancy released buds by the suppression subtractive hybridization procedure. SSH procedure relies on the selective amplification and enrichment of abundant cDNAs in a sample when incubated and hybridized with an excess of a refer ence sample. In the latter work cDNAs isolated by SSH were p
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