New Insight Into Early Somatic Embryogenesis of Mangosteen (Garcinia mangostana) Through de Novo and Comparative Transcriptome Analyses

Somatic embryogenesis in mangosteen (Garcinia mangostana L.), an apomictic and recalcitrant-seeded species, allows stock improvement through genetic manipulation as well as mass propagation in a shortened time. To understand molecular events and gene expression during early somatic embryogenesis of mangosteen, we used RNA-Seq technology and assembled the mangosteen transcriptome de novo. Using the Trinity package, 186,203 transcripts were assembled with a mean size of 767 bp, 34.8 % of which showed significant similarities to known sequences in the GenBank non-redundant protein database. A total of 4001 transcripts were differentially expressed during somatic embryogenesis, while transcripts encoding signalling components of plant hormones such as auxin and cytokinin were significantly enriched. All the cytokinin-related genes were up-regulated, while some auxin-related genes were down-regulated and others were up-regulated. Somatic embryogenesis candidate genes such as SERK2, AGL15, CLVs, WUS and PIN1 were up-regulated in somatic embryos. Zinc finger and MADS family transcription factor genes were among the most presented differentially expressed transcripts in early somatic embryogenesis. Further qRT-PCR analysis confirmed the expression levels of the candidate genes. This study reports a de novo transcriptome assembly and analysis of gene expression during early somatic embryogenesis of mangosteen. Differentially expressed genes reveal that cytokinin has critical role in triggering somatic cell dedifferentiation and induction of somatic embryogenesis in mangosteen. The present work can serve as an important resource for further functional studies in woody plant embryogenesis.