Effects of light quality on the growth,physiology,and secondary metabolism in tissue-cultured seedlings of Pholidota cantonensis and transcriptome analysis
To investigate the effects of light quality on the growth,physiology,and secondary metabolism of Pholidota cantonensis Rolfe,the differences in growth,differentiation,physiological indexes,and the content of secondary metabolites in tissue-cultured seedlings of P.cantonensis under four monochromatic light treatments of red light,yellow light,green light,and blue light as well as five mixed light treatments with the ratio of red to blue light of 1∶4,1∶2,1∶1,2∶1,and 4∶1 were studied.Additionally,transcriptome analysis was performed on the pseudobulbs of tissue-cultured seedlings of P.cantonensis under the optimal light quality treatment.The results indicate that under the ratio of red to blue light of 1∶2 treatment,the tissue-cultured seedlings of P.cantonensis exhibit the many differentiated buds,best growth,and the greatest increase in fresh mass,and the pseudobulbs show the highest contents of total flavonoids,total phenols,and bibenzyls,which are significantly(P＜0.05)higher than those in the white light(the control)treatment,with increases of 23.59％,26.22％,and 34.41％,respectively.Compared to the white light treatment,the activity of superoxide dismutase in the leaves of P.cantonensis tissue-cultured seedlings is the highest under the ratio of red to blue light of 1∶4 treatment,with an increase of 12.34％;the activities of peroxidase and catalase are the highest under the green light treatment,showing increases of 182.34％and 65.43％,respectively;the activity of phenylalanine ammonia-lyase is the highest under the red light treatment,with an increase of 28.66％;the content of soluble protein is the highest under the ratio of red to blue light of 1∶1 treatment,exhibiting an increase of 22.90％;the content of soluble sugar is the highest under the red light treatment,with an increase of 33.76％.The results of principal component analysis and comprehensive evaluation of ten indexes of tissue-cultured seedlings of P.cantonensis indicate that the ratio of red to blue light of 1∶2 is the optimal light quality.The result of transcriptome analysis reveals that a total of 764 differentially expressed unigenes are identified in the pseudobulbs of tissue-cultured seedlings of P.cantonensis under white light and the ratio of red to blue light of 1∶2 treatments.Using the GO database,409 differentially expressed unigenes are annotated into 69 terms across three main categories:biological process,cellular component,and molecular function.Using the KEGG database,21 differentially expressed genes are significantly enriched in four KEGG pathways.Under the ratio of red to blue light of 1∶2 treatment,the expressions of the differential expressed genes CYP86A1,CYP86B1,FAR,HHT,and CER1,which are involved in the cutin,suberine and wax biosynthesis pathway,are significantly increased compared to the white light treatment;the expressions of differential expressed genes C4H,CHS,and F3H,which are associated with the flavonoid,stilbenoid,diarylheptanoid and gingerol biosynthesis pathways are also increased,while the expression of CCoAOMT is decreased.In summary,the ratio of red to blue light of 1∶2 treatment promotes the growth of P.cantonensis tissue-cultured seedlings by enhancing the activity of superoxide dismutase and the content of soluble sugar,as well as up-regulating the expressions of CYP86A1,CYP86B1,FAR,HHT,and CER1 are involved in the cutin,suberine and wax biosynthesis,and the increase in the contents of three secondary metabolites is likely correlated with the up-regulation of C4H,CHS,and F3H in the biosynthesis pathways of flavonoid,stilbenoid,diarylheptanoid,and gingerol.
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