Project description:Dendrobium catenatum (D. catenatum) has long been used as an important medicinal herb in oriental medicine. Polysaccharide, flavonoid, and alkaloid are the major active ingredients, the production and accumulation of which are frequently affected by many environmental factors including water, temperature, and mycorrhizal fungus. However, how phytohormones frequently used in orchid tissue culture regulate the production of active components in D. catenatum is far from clear. Here, major medicinal metabolites were comparatively analyzed in 2-month-old D. catenatum seedlings exposed to phytohormones (0.1 mg/L NAA and/or 1.0 mg/L 6-BA) for three weeks, and eight transcriptomes (two replicates each) corresponding to the treatments were generated. Results demonstrated that the phytohormones triggered transcriptional reprograming, analysis of which revealed a tight association of β-glucosidase (BGLU) expression with the accumulation of polysaccharide. Subsequently, a second RNA-sequencing was further conducted to reveal that a relatively short period (2 w) of varied concentrations of 6-BA application might initially reduce BGLU expression and polysaccharide content and then increase their levels with prolonged treatments (4 w). The RNA-seq data was reconfirmed by functional analysis that 6-BA induced polysaccharide production, while knockdown of BGLU2L resulted in decreased polysaccharide levels. Therefore, the present study clearly demonstrated that BGLU is a key regulator for polysaccharide production and that it is extremely susceptible to NAA and 6-BA treatments in D. catenatum.
Project description:Orchid Dendrobium Sonia (Sonia) has wide demand in floral market throughout the world due to its vibrant coloured flowers, flowering recurrence and dense inflorescence. Effects of different monochromatic light qualities (red, far-red, blue, white) on different developmental and growth responses such as seed gemination, shoot and root growth, chlorophyll and carotenoid accumulation were studied in Sonia. Asymbiotic seed germination was the highest under blue or white light (80%, p<0.001) and least under far-red (55%, p<0.001) suggesting that it could either be controlled by an exceptional novel function of Cryptochrome 1 or the blue wavelengths perceived by PHYA or PHYB in Sonia. All analyses were done in 6-months-old plants till 1 year of age. Shoot length increased significantly in white or red light (3.7-fold, 3.5-fold respectively) while was least under far-red (decreased by 1.6-fold) indicating the major regulatory role of PHYB for shoot growth. Root growth in red in Sonia was more similar to hypocotyl adventitious root (HAR) formation genetically considering PHYB transcript expression. We suggest that the root growth (HAR) under red in Sonia is partly attributed to PHYB, negatively regulated with HY5 transcription factor and positively associated with auxin biosynthesis and accumulation gene BABY BOOM (BBM2) and efflux carriers such as LIKE AUXIN RESISTANT 2 and 3 (LAX2, LAX3). Highest chlorophyll content under far-red and blue might be a hyper-response of SAR under FR light in Sonia. Taxonomic tree analysis finds Sonia closer to Phalenopsis and Dendrobium catenatum Lindl. The three phytochromes and one cryptochrome sequences which were similar to PHYA, B, C and CRY1 respectively. CRY1 was retrieved with one more isoform CRY1_X2, with all these sequences more similar to those of Oryza.sativa. Further study can clarify the indicating reason of a probable gene loss which is evident from the absence of any sequence similar to CRY2 in root RNA isolates of Dendrobium Sonia.