Mechanism Of Physiological Characteristics Of Leaf Color In Camellia Sinensis Cv.Huangjinya Response To Light Quality

Camellia sinensis?L.?O.Kuntze.cv.Huangjinya is a light-sensitive yellow tea cultivar that has been successfully bred in recent years.The leaf color is mainly regulated by light,and shows yellow variation in the whole year.The ornamental and economic value of Huangjinya are enhanced due to its yellow fresh leaf,dry tea,soup and infused leaf.However,during the growth and development of Huangjinya,the leaf sunburn is easily caused by light,affacting the leaf color and tea quality.Therefore,the study on analyzing the mechanism of Huangjinya leaf color from the perspective of light quality and photoreceptor is of great significance to understand the photosensitive yellowing of Huangjinya leaves,and provides a theoretical basis for improving the excellent quality characteristics by adopting reasonable light and molecular measures.In this study,the effects of light quality on the color of Huangjinya leaves were analyzed by using different color shade nets and LED bulbs.Transcriptome sequencing was used to investigate the regulation of gene expression levels in Huangjinya leaves by different spectra at the molecular level.Genes,involved in photosystem,photosynthetic pigment metabolism and photoreceptor that were closely related to leaf color,were screened The important photoreceptor gene,PHY?photochrome?,was cloned and bioinformatics and expression patttern in Huangjinya leaves under different light quality were analyzed.The main results were as follows:1.Due to its high light sensitivity,the leaves of Huangjinya without shading in summer and autumn has lower chlorophyll content.However,at the same time,the photosynthetic capacity and anti-stress ability of tea plants were weaker,which was easy to cause leaf burns.The daily PAR values of 216⁶30?mol·m^-2·s^-1?70%black shading treatment?was appropriate for promoting the growth of Huangjinya plants at the seedling stage.For mature tea plants,daily PAR values of 324⁹90?mol·m^-2·s^-1?55%black shading treatment?could be used to keep the yellowing characteristics and to effectively improve biochemical quality,so as to give full play to its variety characteristics.The leaf color of Huangjinya grown under blue shade net showed greener than those grown under black shade net.2.The leaf color of Huangjinya exposed to white light was yellowest,followed by blue light.Red light obviously promoted leaf turned to green,and the significant increase of chlorophyll content.Compared with white light,there was lower photosynthetic pigment content in Huangjinya leaves treated with ultraviolet along with significantly decreased F_v/F_m and?PSII,and elevated NPQ,indicating obvious light inhibition.The NPQ in red light was also significantly higher than white light,which showed that a higher energy consumption was required to protect optical system.In addition,blue light had a significant effect on the growth of new shoots and the expansion of leaf of Huangjinya.3.Compared with white light,the genes involved in photosynthetic system and photosynthetic pigment synthesis pathway in Huangjinya leaves treated with ultraviolet light were significantly downregulated,thus inhibiting the photosynthesis and growth.A large number of DEGs?such as IAA,POD,HCT and CAD?involved in plant hormone signal transduction and phenylpropanoid biosynthesis pathway were significantly downregulated,which inhibited the signal transduction of growth promoting hormone and the production of secondary metabolites such as flavonoids and lignin in plants.PHYs were significantly downregulated in Huangjinya leaves irradiated by ultraviolet light.It is speculated that ultraviolet light could reduce secondary metabolite content,weaken resistance and cause leaf sunburn by inhibiting light signal transduction involving PHY.4.The positive effect of red light on chlorophyll accumulation was mainly due to downregulated chlorophyll degradation-related genes?e.g.Chlase?,and upregulation of POR,CHLH,LHCA and LHCB,so as to enhance the ability to capture chlorophyll.The expression of PHYs were higher in Huangjinya leaves under red light,which indicating that could Huangjinya could transmit red light signal through PHY,regulate the downstream chlorophyll synthesis and the expression of photosynthetic system-related genes,and then promote the leaf color to turn green.5.It was speculated that yellow-green light could downregulate the expression of POR and HSP70 in Huangjinya leaves,inhibiting chlorophyll biosynthesis and chloroplast development,and thus inducing yellow leaves.Photochrome might also play an important role in yellowing process of Huangjinya leaves by yellow-green light.6.Five ORF sequences of CsPHY were successfully cloned.The lengths were 3384,4038,3018,3294 and 3045 bp,and encoded 1127,1345,1005,1097 and 1014 amino acids,respectively.The CsPHY family had six typical conserved domains,which were important for tea plants to sense and conduct light signal.CsPHY were all acidic unstable proteins,with the highest proportion of leucine,and without transmembrane region or signal peptide.CsPHYA1and CsPHYB2 were located in chloroplasts,CsPHYA2 and CsPHYB1 were located in mitochondria,and CsPHYE were possibly located in cytoplasmic matrix.Alpha helix and random coil were the main structural elements of CsPHY.Phosphorylation of CsPHY were mainly occurred in the form of serine.CsPHYA1 and CsPHYA2,CsPHYB1 and CsPHYB2were closely related to AdPHYA and AdPHYB of Actinadia deliciosa,respectively.CsPHYE was closely related to PvPHYE of Pistacia vera.CsPHYs were also highly similar to Arabidopsis thaliana AtPHYs in amino acid sequences,which predicted they had similar functions in sensing and conducting light signal,and in regulating the expression of downstream light-induced genes and affecting chlorophyll accumulation.The expressions of CsPHYA and CsPHYB2 were significantly increased after red light irradiation,among which,CsPHYB2 with higher abundance might have more obvious effects on promotion of chlorophyll accumulation in plants responded to red light.