Effects of light quality on the berry coloration and quality of Red Globe grape during veraison based on transcriptome sequencing

Abstract:【Objective】Greenhouse grape has the characteristics of early berry bearing and high benefit, which has developed rapidly in Ningxia and significantly improved the economic benefit of local grape industry. Red Globe grape is the main variety of table grape in Ningxia, which has the characteristics of big ear, brilliant color, sweet taste, storage tolerance and high yield, etc. However, under the condition of protected cultivation, weak light and poor light quality will affect the color set and maturity of grapes, resulting in the decline of grape yield and quality, which restricts the sustainable development of protected grape industry. As the main environmental factor for the growth and development of protected horticultural crops, light not only affects the photosynthetic capacity of protected horticultural crops, but also participates in the regulation of various physiological processes. As an effective measure to im- prove lighting conditions in facilities, LED light supplement can accurately regulate spectral composi- tion, and is widely used in facility cultivation research. Transcriptome sequencing has been applied in the study on gene structure, function and expression, it is also an important method for phenotypic cor- relation research, which plays an important role in exploring the molecular mechanism of plant, parsing facility grape berry coloring and quality influencing factors, and helping to improve the grape commodi-ty value, so as to improve the economic benefits of grape planting. 【Methods】The experiment was car- ried out in the shade of the solar greenhouse from April to September, 2019. The eight-year-old Red Globe grapes were used as experimental materials, and four different kinds of light quality treatments were set up in this experiment. They were red blue light (red light: blue light = 2:1), blue light, red light and white light, with no supplementary light as the control. Twelve vines with the same growth vigor were selected for each treatment and divided into 3 replicates with 4 vines in each replicate. Supplemen- tary light lamps were placed 30 cm above the tree in the test row, and 6 supplementary light lamps were set for each treatment. All treatments were separated by reflective film. Lightening started from April 2019, from 8:00 to 20:00 every day, with a light intensity of 200 μmol · m-2 · s-1, until the end of berry rip- ening and harvesting. The net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 con- centration (Ci) and transpiration rate (Tr) of grape leaves were measured at the berry-color-turning stage. The contents of anthocyanins, reducing sugars, titratable acids and soluble solids in the berry were deter- mined, and transcriptome sequencing was performed on the pericarp. The gene expression was calculat- ed using FPKM and the screening criteria were differential expression multiple |log2fold changes|≥1 and p-adjust < 0.05. The differentially expressed genes in the gene collection were compared with GO and KEGG databases to obtain the functional annotations and related metabolic pathway information of the genes in different samples. In order to verify the accuracy of RNA-seq data, 9 differentially ex- pressed genes were randomly selected for real-time fluorescence quantitative expression verification analysis.【Results】Red light increased the net photosynthetic rate and transpiration rate of leaves, while blue light increased stomatal opening and intercellular CO2 concentration. Different light quality had dif- ferent effects on the photosynthetic performance of Red Globe grape leaves, and supplemental light could promote the photosynthesis of leaves. Blue light treatment had the best effect on improving berry color and quality, followed by red blue light, white light and red light. A total of 1313 differentially ex- pressed genes were obtained in all the samples, including 728 up-regulated genes and 585 down-regulated genes, among which 638, 434, 375 and 320 differentially expressed genes were detected between red and blue light, blue light, red light, white light treatment and control, respectively. GO analysis showed that differential genes were closely related to metabolic process, cellular process, membrane, catalytic activity, binding and other items. Enrichment analysis of KEGG pathway found that the differential genes were mainly involved in photosynthesis, flavonoid biosynthesis and starch and sucrose metabo- lism pathways. Different light quality affected grape berry coloration and quality by regulating the ex- pression of related genes such as grape photosynthesis, flavonoid biosynthesis, and starch and sucrose metabolism. Nine differentially expressed genes were randomly selected according to the enrichment re- sults, and the gene expression trend was consistent with the results of transcriptome sequencing by qRT-CR.【Conclusion】Different light quality affected plant photosynthesis, further influencing the synthe- sis of organic matter such as sugar and amino acid. Light quality regulated the expression of genes relat- ed to the process of anthocyanin metabolism and the synthesis of anthocyanin. Blue light and white light significantly promoted the biosynthesis of anthocyanin in berry. Different light quality promoted the accumulation and conversion of starch and sucrose in berry, and improved berry quality. The up-reg- ulated expression of INV, SPS, HK and BG genes in berry accelerated the sucrose metabolism and in- creased the accumulation of reducing sugars, while reducing sugars and soluble solids may have a pro- moting effect on the synthesis and accumulation of anthocyanins. Trehalose related genes were signifi- cantly up-regulated in white light, blue light and red blue light, suggesting that trehalose related genes played an important role in grape environmental adaptability. In addition, it was also found that supple- menting light affected the metabolism of some amino acids and the expression of endogenous hormone-related genes in berry, which may also be the important factors causing the differences in color and qual- ity of grapes among different treatments.