Effects Of Light On The Regulation Of Anthocyanin Synthesis In Purple Tea Plant And Physiological Response Of Tea Plant To Light Quality

Tea plant(Camellia sinensis(L.)O.Kuntze)is an important economic crop and one of the three soft drink crops in the world.It is rich in tea polyphenols,amino acids,caffeine,anthocyanins and other bioactive substances.The anthocyanin content of the new shoots of purple tea plant is high,and the young shoots are red or purple in spring,summer and autumn.Light is one of the important environmental factors that affect synthesis of anthocyanins in plants,but the molecular mechanism of light(including light quality,light intensity and photoperiod)regulating anthocyanin synthesis in new shoots of purple tea plant has been rarely reported.Therefore,in this paper,the ‘Ziyan’tea seedlings are used as materials to systematically study the effects of light quality,light intensity and photoperiod on the anthocyanin synthesis of purple tea,and to reveal the molecular mechanism of anthocyanin biosynthesis in purple tea plant from enzymology and transcription level.The effects of different light qualities on the physiology,biochemistry and photosynthesis of purple tea plants were also studied.These studies provided the necessarily experimental support and theoretical basis for improving the anthocyanin content of fresh leaves of tea plant by adjusting light and other cultivation management measures.The main results are as follows:1.Compared with white light,red light and blue light can significantly increase the component content and total content of anthocyanin of new shoots in ‘Ziyan’,and blue light has the strongest promoting effect.The content of delphinidin(Dp),cyanidin(Cy)and pelargonidin(Pg)and total content in new shoots treated by blue light increased by 27.52%,42.58%,102.72% and 29.64%,respectively.Through transcriptome sequencing analysis,580 differentially expressed genes(DEGs)were identified between white light and red light,among which 295 genes were up-regulated and 285 genes were down-regulated.There were 543 DEGs between white and blue light treatment,including 242 were up-regulated and 301 were down-regulated.Among the DEGs of white light and red light,white light and blue light,one DEG enriched into anthocyanin synthesis pathway and two DEGs enriched into flavonoid synthesis pathway.Compared with white light,red and blue light can significantly improve CHS,F3’H,F3’5’H and ANS activities,thus promoting anthocyanin synthesis and accumulation.2.Compared with white light treatment,UV-A,UV-B,UV-A-UV-B mixing light(1:1)(UV-AB)treatment can significantly improve the components content and total content of anthocyanin in new shoots of ‘Ziyan’,and UV-A has the strongest promoting effect,the contents of Dp,Cy,Pg and total content in the new shoots increased by64.57%,80.12%,49.34% and 65.94%.than control.After UV treatment,the activity of CHS,F3’H,F3’5’H and ANS in the new shoots increased,while the LAR activity decreased,which further promoted the synthesis of anthocyanins and inhibited the synthesis of catechins.In addition,UV treatment also significantly reduced the chlorophyll content.The transcriptome sequencing analysis revealed that there were146DEGs(47 up-regulated,99 down-regulated)were identified between white light and UV-A treatment,298 DEGs(137 up-regulated,161 down-regulated)were identified between white light and UV-B treatment,and 121 DEGs(52 up-regulated,69 downregulated)were identified between white light and UV-AB treatment.The transcription factors TT8 and TT2 treated by UV-A were significantly up-regulated,while the negative regulator MYB4 was significantly down-regulated.b HLH3 was up-regulated,while C1 and MYB110 were down-regulated significantly under UV-B treatment.EGL1 and TT2 were up-regulated under UV-AB treatment.These transcription factors may be involved in regulating the expression of structural genes in anthocyanin biosynthesis pathway,thus promoting anthocyanin synthesis and accumulation.3.The treatment of ‘Ziyan’ tea seedlings with different light intensities found that the anthocyanins content of new shoot increased with the increase of light intensity.The content of Dp,Cy,Pg and total content in the new shoots were 124.21%,63.43%,57.21%and 105.88% higher in high light intensity treatment than those in low light intensity treatment.Transcriptome sequencing analysis revealed that there were 1349 DEGs(404up-regulated genes and 945 down-regulated genes)between low and high light intensity treatment.Among the differential expression genes,2 structural genes(F3’H and UFGT)and 5 transcription factor genes(MYB44,MYB75,MYB48,b HLH 162,and WRKY40)involved in the flavonoid metabolism pathway were identified.The above results indicate that light intensity can regulate the expression levels of regulator gene and structure gene in the flavonoid pathway,and then increase the enzyme activity to promote the anthocyanins synthesis and accumulation in the new shoot of ‘Ziyan’.The enzyme activity of anthocyanin synthesis pathway also increased with the increase of light intensity.4.After treatment with different photoperiod,anthocyanin component content and total content in new shoots of ‘Ziyan’ were increased significantly with the extension of illumination time.The contents of Dp,Cy,Pg and total content in long day treatment were 178.10%,92.37%,50.40% and 148.76% higher than in short day treatment.Through transcriptome sequencing analysis,the regulatory genes MYB1,MYB73,MYB111,MYB48,MYB75,MYB113,MYB5,MYB12,MYB5 a,MYB5b and WRKY41 involved in anthocyanin synthesis were identified and differentially expressed between short and long day treatment.Under long day treatment,all structural genes involved in anthocyanin synthesis were up-regulated,and the enzyme activity involved in anthocyanin synthesis was significantly increased.The results showed that long day treatment activated the expression of structural genes by regulating genes,and enhanced the enzyme activity and then promoted anthocyanins biosynthesis.5.In summary,different light factors had different effects on anthocyanin synthesis and accumulation in ’Ziyan’ shoots.In different light quality treatments,red light and blue light have similar enzyme activity and enzyme gene expression levels on the anthocyanin synthesis pathway.Red light and blue light increase CHS,F3’H,ANS activity,and blue light also increase F3’5’H activity.In addition to ANS,the enzyme activities of other enzymes were consistent with the corresponding gene expression trend;UV treatment increases the activity of CHS,F3’5’H,ANS,and UV-A also increased the activity of CHI,F3’H.These enzyme activity and trend of the expression of corresponding enzyme gene were more consistent.Under different light intensity and photoperiod treatment,the activities of all enzymes involved in anthocyanin synthesis were increased under high light intensity and long day treatment,which was consistent with the trend of enzyme gene expression.The transcription factors identified in light quality,light intensity,and photoperiod treatment that may be involved in the regulation of anthocyanin synthesise were quite different.6.Compared with other light quality treatments,red light and white light treatment are more conducive to the growth of ‘Ziyan’ new shoots.And red light also promoted the increase of leaf antioxidant enzyme activity.After 20 days of treatment,blue light treatment was beneficial to accumulation of proline,soluble sugar and soluble protein in purple tea plant,and red light and red-blue mixing light were beneficial to increase of photosynthetic pigment content in purple tea plant.However,with the extension of treatment time,the net photosynthetic rate of purple tea plant treated with different light quality was decreased.After 20 days treatment,compared with the control,the Fv/Fm of red light treatment decreased by 13.12%,and the Fv’/Fm of red blue combination increased by 45.75% and 75.94%,and the Phi PS2 was decreased in all light quality treatment in ‘Ziyan’.The above results showed that the effects of different light quality on the physiological,biochemical photosynthesis and chlorophyll fluorescence parameters of purple tea plant were quite different,and the effects of the same light quality on the above indexes of purple tea plant were also different in different periods.