Effects Of Different Light Quality On Photomorphogenesis In Brassica Napus

Light is one of the essential environmental factors affecting plant growth and development,including photomorphogenesis.During the initial phase of seed germination,the seedlings grow with rapid elongation of hypocotyls in the dark(in the soil).After the seedlings emerge from the soil and are exposed to sunlight,the chloroplasts are gradually synthesized and the photosynthesis is activated.The changes in plant morphology induced by light exposure are the result of co-regulatory of many genes in light signaling pathways.Many studies showed that the network of light signals does not exist independently,since light signals usually coordinate with other environmental factors such as high/low temperature,as well as hormones(auxin,gibberellin,brassinosteroids,etc.)to regulate plant growth and development together.Therefore,the regulatory network of photomorphogenesis is very complicated.Presently,most researches on photomorphogenesis are based on the model plant Arabidopsis thaliana,while there are few studies on other plants or crops.The current study aims to unravel the physiological and molecular mechanisms on photomorphogenesis in Brassica napus at transcriptome,metabolome and comparative genomics levels.The main findings are as follows:1.We determined the transcriptome of rapeseed seedlings(hypocotyls and cotyledons)under different light qualities(white light,blue light,red light,far-red light,and darkness)using RNA-sequencing.Principle component analysis(PCA)and hierarchical cluster analysis showed that the transcriptional patterns under dark/red light were distinct from those under blue/far-red light,which partially explained the observed phenotypes that red light treated plants showed longer hypocotyl than blue and far-red light treated plants.We investigated the gene expression of the key regulators in light signaling and downstream pathway,and displayed a comprehensive overview on their contribution to photomorphogenesis under different light quality.The results can improve the understanding on transcriptional regulation of photomorphogenesis in B.napus,and provide clues for future work.2.We measured the metabolite concentrations in hypocotyls and cotyledons during morphogenesis of rapeseed(cultivar ZD622)under different light quality treatments using UPLC-Q-TOF/MS.The results showed that flavonoids in the cotyledons were always maintained at a high level in dark,which may enable young seedlings to adapt to UV-B radiation under sunlight.Along with the prolongation of light treatments,the concentrations of flavonoids in hypocotyls increased gradually,which may protect the young hypocotyls from the insect.Moreover,the concentrations of hydroxycinnamic acids and their derivates increased gradually in response to blue light,which may have roles in the synthesis of lignin and cell wall.Overall,it is concluded that the synthesis,transport and degradation of flavonoids,hydroxycinnamic acids and their derivates may facilitate the growth and development of seedlings.3.We measured the hypocotyl lengths of 267 rapeseed cultivars from all over the world under different light quality treatments.Genome wide association studies(GWAS)of hypocotyl lengths identified four candidate genes regulating hypocotyl elongation.These genes included Utp21(under white light),RFI2(under blue light),HDA15(under red light)and H2B(under far red light).These findings provide clues for the future work on studying the molecular mechanism of photomorphogenesis in Brassica napus.4.We explored the origin and evolution of light signaling genes or gene families in 38 representative species from algae to land plants using bioinformatics tools.In addition,we performed phylogenetic analysis of PIF gene family,and revealed the structural variation and gene family expansion process of the PIF gene family.These results reaveled the differences on mechanism of photomorphogenesis among different species to certain extent,which improves the understanding the origin and diversification of light signaling genes.In conclusion,this study elaborated photomorphogenesis under different light quality of Brassica napus from four aspects: transcriptome,metabolome,genome-wide association analysis(GWAS),and phylogenetic analysis.The findings not only improve the understanding of the mechanism in light morphogenesis in rapeseed,but also provide the guidances for setting up precise light conditions(light quality ratio,photoperiod,etc.)during the growth of rapeaeed in the greenhouse or plant factory.