The Establishment of an Agrobacterium-Mediated Transformation Platform for the Non-Embryogenic Calli of Vitis vinifera L.

Non-embryogenic calli （NEC） was inevitably and heavily produced when grape embryogenic calli （EC） was induced from explants or during the subculture of EC.A stable and highly efficient NEC transformation platform is required to further sort out and verify key genes which determine/switch the identity of NEC and EC.In this research,a vector pA5 containing a chitinase signal sequence fused to gfp （green fluorescent protein） and an HDEL motive was used to target and immobilize into Agrobacterium strain EHA105 to establish a transformation platform for Vitis vinifera L.cv.Chardonnay NEC.It was determined that NEC 10 d after subculture was the best target tissue;30 min for inoculation followed by 3 d co-cultivation with the addition of 200 μmol L-1 acetosyringone （AS） was optimized as protocol.The use of bacterial densities as 1.0 at OD600 did not result in serious tissue hypersensitive reaction and it had higher efficiency.Kanamycin at 200 mg L-1 was picked for positive expression selection.The stable transformation of NEC was proved by reverse transcription-polymerase chain reaction techniques （RT-PCR） and fluorescent microscopy after three sub-cultures of the selected cell line.Highly efficient genetic transformation protocol of grape NEC was achieved and some of the optimized parameters were different from that reported for EC.This transformation platform could facilitate the verification of candidate somatic embryogenesis （SE） decisive genes,and the successfully transformed NEC with certain genes can also be used as bioreactors for the production of functional products,as NEC not only proliferates fast,but also keeps in a rather stable condition.

Comparative transcriptome study provides insights into acquisition of embryogenic ability in upland cotton during somatic embryogenesis

Background： The conversion from non-embryogenic callus （NEC） to embryogenic callus （EC） is the key bottleneck step in regeneration of upland cotton （Gossypium hirsutum）, and hinders the transgenic breeding of upland cotton. To investigate molecular mechanisms underlying acquisition of embryogenic potential during this process, comparation analysis of transcriptome dynamics between two upland cotton cultivars with different somatic embryogenesis abilities was conducted. Results： Differentially expressed genes involved in the transformation from NEC to EC were detected in the two different cultivars. Principal component analysis based on DEGs showed that the NEC tissues of the two cultivars were highly heterogeneous, whereas the derived EC tissues were similar, which suggested the homogeneousness of EC between different lines. In the highly embryogenic cultivar CCRI 24, more of these genes were down-regulated, whereas, in the recalcitrant cultivar CCRI 12, more were up-regulated. Bioinformatics analysis on these DEGs showed that the vast majority of differentially expressed genes were enriched in metabolism and secondary metabolites biosynthesis pathways. Flavonoid biosynthesis and phenylpropanoid biosynthesis pathways were enriched in both cultivars, and the associated genes were down-regulated more in CCRI 24 than in CCRI 12. We deduced that vigorous secondary metabolism in CCRI 12 may hinder primary metabolism, resulting in tardiness of cell differentiation. Interestingly, genes involved in the plant hormone signal transduction pathway were enriched in the recalcitrant cultivar CCRI 12, but not in CCRI 24, suggesting more radical regulation of hormone signal transduction in the recalcitrant cultivar. Signal transduction rather than biosynthesis of plant hormones is more likely to be the determining factor triggering NEC to EC transition in recalcitrant cotton lines. Transcription factor encoding genes showed differential regulation between two cultivars. Conclusions： Our study provides valuable information about the molecular mechanism of conversion from NEC to EC in cotton and allows for identification of novel genes involved. By comparing transcriptome changes in transformation from NEC to EC between the two cultivars, we identified 46 transcripts that may contribute to initiating embryogenic shift.