Transcriptomic Analysis Of The Morphology And Glucosinolate Metabolism In Chinese Kale With Supplemental Far-red Light

Chinese kale（Brassica alboglabra Bailey）,an original Chinese cruciferous vegetable,is distributed widely in South China and Southeast Asia.The flower stalk and leaves are the edible part.In this study,the Chinese kale cv.‘Lv Bao’were cultivated under white light-emitting diodes（LEDs）with photosynthetic photon flux density（PPFD）of 250μmol m^–1 s^–1 and photoperiod（6:00 to 18:00）in the plant factory with artificial lighting.There were three supplemental far-red light treatments:0 W/m²（CK）,3 W/m²（FR-3）and 6 W/m²（FR-6）.The transcriptomics analysis and the agronomic traits,biomass,and health-promoting compounds were combined to investigate the regulation mechanism of far-red light on morphological changes and glucosinolate metabolism.The main results were as follows:1.Far-red light had significant influence on plant morphology of Chinese kale.Along with the increased intensities of supplemental far-red light,plant display,plant height,internode length,leaf length,leaf width and leaf area obviously improved,while the angle between leaf and stem decreased.2.Far-red light accelerated the transformation from vegetative growth to reproductive growth of Chinese kale,which significantly increased the flower budding rate at 60 days after sowed.At the same time,far-red light increased the chlorophyll contents and biomass of Chinese kale,while markedly decreased its root and shoot ratio.3.Far-red light limited the accumulation of nitrogen and potassium in Chinese kale,while enhanced the contents of calcium and magnesium in roots.4.Far-red light weakened the antioxidant activities of Chinese kale,DPPH radical inhibition percentage（DPPH）,ferric ion reducing antioxidant power（FRAP）,contents of total phenolic compounds（TPC）and total flavonoids（TF）decreased.5.In this study,nine glucosinolates（GLS）were detected.The contents of total GLS,aliphatic GLS and indolic GLS significantly decreased under far-red light.8 kinds of GLS had the similar decreased trend with total GLS,while the content of4-Hydroxyglucobrassicin（4OH）increased in FR-3 treatment.6.A c DNA library of Chinese kale apical meristem was constructed by RNA-seq（Illumina Hi Seq2000）.Approximately 75.3 GB clean reads were obtained,and a total of145746 unigenes were formed by initial sequence splicing,with an average read length of1356 bp.Among these,133129 unigenes（91.34%）were annotated based on at least one database.In pairwise comparisons of CK vs FR-3,CK vs FR-6 and FR-3 vs FR-6,there were respectively 455,893 and 310 unigenes identified as differentially expressed genes（DEGs）.KEGG enrichment analysis revealed that DEGs were significantly enriched in‘photosynthesis-antenna proteins’,‘glucosinolate biosynthesis’,‘circadian rhythm-plant’and‘plant hormone signal transduction’pathways.GO enrichment analysis suggested that DEGs were related to‘chorophyll binding’,‘photosystem’,‘light-harvesting complex’and‘glucosinolate biosynthetic process’.These indicated that the effects of far-red light on Chinese kale were involved in chorophyll biosynthesis,plant growth and morphology,flowering and GLS metabolism.7.Based on brassica database,210 genes were identified as GLS biosynthesis genes homologous to Arabidopsis thaliana,including chain elongation genes（23 genes）,core structure formation genes（39 genes）,side chain modification genes（31genes）,co-substrate pathways（14 genes）,GLS breakdown genes（74 genes）and GLS-regulated transcript factors（29 genes）.In chain elongation step,8 genes annotated MAM1,IPMDH and Leu D1were downregulated by far-red light.In core structure formation step,9 genes identified as CYP79F1,CYP83A1,Stc and UGT74B1 were also downregulated by far-red light.8.To determine the optimal reference gene for q PCR analysis under far-red light,this study analyzed 8 candidate reference genes（ACT、TUB、UBC、GAPDH、UBQ、EF1、PP2A和CYP21）and found that UBQ and EF1 were the best choice for normalization in different intensities of far-red light treatments.And,q PCR analysis revealed that the relative expressions of randomly selected 14 DEGs were in accordance with RNA-seq.