Plant regeneration via somatic embryogenesis (SE) is the key step for genetic improvement of cotton (Gossypium hirsutum L.) through genetic engineering mediated by Agrobacteria, but the molecular mechanisms underlying SE in cotton is still unclear. Here, RNA-Sequencing was used to analyze the genes expressed during SE and their expression dynamics using RNAs isolated from non-embryogenic callus (NEC), embryogenic callus (EC) and somatic embryos (SEs). A total of 101, 670 unigenes were de novo assembled. The genes differentially expressed (DEGs) amongst NEC, EC and SEs were identified, annotated and classified. More DEGs were found between SEs and EC than between EC and NEC. A significant number of DEGs were related to hormone homeostasis, stress and ROS responses, and metabolism of polyamines. To confirm the expression dynamics of selected DEGs involved in various pathways, experiments were set up to investigate the effects of hormones (Indole-3-butytric acid, IBA; Kinetin, KT), polyamines, H2O2 and stresses on SE. Our results showed that exogenous application of IBA and KT positively regulated the development of EC and SEs, and that polyamines and H2O2 promoted the conversion of EC into SEs. Furthermore, we found that low and moderate stress is beneficial for proliferation of EC and SEs formation. Together, our global analysis of transcriptomic dynamics reveals that hormone homeostasis, polyamines, and stress response synergistically regulating SE in cotton.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-016-0511-6) contains supplementary material, which is available to authorized users.

Key messageiTRAQ based proteomic identified key proteins and provided new insights into the molecular mechanisms underlying somatic embryogenesis in cotton.AbstractSomatic embryogenesis, which involves cell dedifferentiation and redifferentiation, has been used as a model system for understanding molecular events of plant embryo development in vitro. In this study, we performed comparative proteomics analysis using samples of non-embryogenic callus (NEC), embryogenic callus (EC) and somatic embryo (SE) using the isobaric tags for relative and absolute quantitation (iTRAQ) technology. In total, 5892 proteins were identified amongst the three samples. The majority of these proteins (93.4%) were found to have catalytic activity, binding activity, transporter activity or structural molecular activity. Of these proteins, 1024 and 858 were differentially expressed in NEC versus EC and EC versus SE, respectively. Compared to NEC, EC had 452 and 572 down- and up-regulated proteins, respectively, and compared to EC, SE had 647 and 221 down- and up-regulated proteins, respectively. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis indicated that genetic information transmission, plant hormone transduction, glycolysis, fatty acid biosynthesis and metabolism, galactose metabolism were the top pathways involved in somatic embryogenesis. Our proteomics results not only confirmed our previous transcriptomic results on the role of the polyamine metabolic pathways and stress responses in cotton somatic embryogenesis, but identified key proteins important for cotton somatic embryogenesis and provided new insights into the molecular mechanisms underlying somatic embryogenesis in cotton.

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Polyamines play essential roles in plant development and various stress responses. In this study, one of the cotton S-adenosylmethionine decarboxylase (SAMDC) genes, GhSAMDC 1 , was constructed in the pGWB17 vector and overexpressed in tobacco. Leaf area and plant height increased 25.9-36.6% and 15.0-27.0%, respectively, compared to the wild type, and flowering time was advanced by 5 days in transgenic tobacco lines. polyamine and gene expression analyses demonstrated that a decrease in spermidine and an increase in total polyamines and spermine might be regulated by NtSPDS 4 and NtSPMS in transgenic plants. Furthermore, exogenous spermidine, spermine and spermidine synthesis inhibitor dicyclohexylamine were used for complementary tests, which resulted in small leaves and dwarf plants, big leaves and early flowering, and big leaves and dwarf plants, respectively. these results indicate that spermidine and spermine are mainly involved in the vegetative growth and early flowering stages, respectively. Expression analysis of flowering-related genes suggested that NtSOC 1 , NtAP 1 , NtNFL 1 and NtFT 4 were upregulated in transgenic plants. In conclusion, ectopic GhSAMDC 1 is involved in the conversion of spermidine to spermine, resulting in rapid vegetative growth and early flowering in tobacco, which could be applied to genetically improve plants. Polyamines, including putrescine (diamine), spermidine (triamine), and spermine (tetraamine), play various roles in plants 1,2. Many reports indicate that polyamines are affect the fluidity of the lipid membrane and participate in the biotic and abiotic stress responses 3-9. Furthermore, polyamines have been reported to be involved in various physiological processes 9-14. The polyamine metabolic pathways have been elucidated in plants 15. Putrescine originates from ornithine or arginine, catalysed by ornithine decarboxylase, or arginine decarboxylase, agmatine iminohydrolase and N-carbamoyl putrescine amidohydrolase. Spermidine and spermine are derived from putrescine and are catalysed by spermidine and spermine synthases, respectively. S-adenosylmethionine decarboxylases (SAMDCs) catalyse the S-adenosylmethionine decarboxylation reaction and provide an aminopropyl group, which is involved in spermidine and spermine synthesis. SAMDC transcripts have been analysed in a wide variety of plant species, often with higher transcript levels detected in reproductive than vegetative organs 16-21. Further evidence that polyamines are required for growth and development comes from analysing the Arabidopsis thalian bud2 mutant. This mutant has an inactivated AtSAMDC 4 gene and an enlarged vascular phenotype 22. Moreover, AtSAMDC 1 is involved in an interaction between beet severe curly top virus and Arabidopsis plants 23. Numerous studies have reported upregulation of SAMDC in response to various stressors, including drought, salt, high or low

Intertribal somatic hybrids of Brassica napus and Camelina sativa were developed by protoplast electrofusion. Hybrid identity of the regenerants was determined using flow cytometric analysis of nuclear DNA content and simple sequence repeat (SSR) marker analysis. Three hybrids exhibited specific bands for B. napus and C. sativa. These hybrids showed intermediate leaf, flower and seed morphology compared with the two parental species. The seeds of these three hybrids had a modified fatty acid profile, indicating higher level of linolenic and eicosanoic acids than those of B. napus. Our results suggest that somatic hybridization offers opportunities for transferring entire genomes between B. napus and C. sativa in improving rapeseed breeding.