Differentially expressed genes during the transition from early to late development phases in somatic embryo of banana (Musa spp. AAB group, Silk subgroup) cv. Manzano

A cDNA-sequence-related amplified polymorphism (cDNA-SRAP) approach was used to identify relevant genes expressed at the onset of somatic embryo maturation/desiccation in banana (Musa spp. AAB group, Silk subgroup) cv. Manzano. For this, an embryogenic procedure, starting with cell suspensions, was first improved by including a culture period on a free growth-regulator medium for embryo maturation. This produced an up to 95% germination of the coleoptilar embryos. Gene expression patterns were followed through different stages of the process, including immature male flower explants, embryogenic calli, as well as immature, mature and germinated embryos. A total of 151 differentially expressed transcript-derived fragments (TDFs) were detected, sequenced, resulting in the identification of 71 by their similitude to accessions deposited in different data bases. The participation of four of these genes, putatively involved in the banana somatic embryogenesis, was further analyzed by real-time quantitative PCR (q-PCR). This confirmed their preferential expression at the transition from embryo early development to maturation. Noteworthy, tryptophan aminotransferase relate 2 (TAR2), which is involved in the indole-3-pyruvic acid dependent auxin biosynthesis, corresponded to one of the upregulated four genes, suggesting the requirement of this growth regulator at the transition stage. This study opens the path for future in-depth studies of molecular and biochemical events occurring during in vitro somatic embryogenesis in edible bananas.