Genetic Analysis Of Red Character In Lettuce And Its Effect On Agronomic Characters

Red lettuce is red because of its rich anthocyanin.Although the regulation of anthocyanin synthesis has been studied in lettuce,there are still unknown regulatory pathways.In this study,it was found that in an F_3:4color segregating population,the leaves were separated from light red and dark red,and light red was the dominant trait.Using the specific molecular markers of the genes that regulate the redness of lettuce leaves cloned earlier in the laboratory,it was found that the genotypes of these genes in the light red and dark red plants are consistent,indicating that there are new loci that control the formation of redness in lettuce leaves.The BSR-seq method was used to determine the locus that controls the redness of lettuce in the 273-315Mb region of chromosome 5.After using a total of about 2,000 individual plants for fine mapping,the target gene was located in the 293.4-300.0Mb region of chromosome 5,about 6.6Mb,and named Red Leaf Lettuce 7（RLL7）.There are amino acid changes in the two candidate genes in the analysis mapping segment,and there is also a difference in the sequence of one LncRNA.It is speculated that the above two genes or LncRNA are the main factors regulating the formation of redness of lettuce leaves in this population.Their CRISPR/Cas9 knockout vectors were constructed,and some T₀positive seedlings were obtained by genetic transformation（phenotype remains to be seen）.There were significant differences in the plant height of light red and dark red lettuce after bolting in the isolated population,and the average plant height of light red lettuce was higher than that of dark red lettuce.The stem cells of dark red and light red lettuce were observed by paraffin section.The cross section of the stem showed that the number of light red lettuce cells was more than that of dark red lettuce.It was speculated that the difference in height between light red and dark red lettuce after bolting may be due to the stem due to differences in cell numbers.Since plant height is usually affected by hormones,10 hormone-related genes were analyzed semi-quantitatively.It was found that the expression of gibberellin synthesis-related genes in dark red lettuce stems was lower than that of light red lettuce,while the expression of auxin-related genes was higher than that of light red lettuce.The dark red lettuce obtained in this study is the aggregation of all the genes that positively regulate anthocyanin synthesis cloned in the laboratory.In order to study the changes of anthocyanin synthesis of dark red lettuce in the isolated population under different light conditions,the modified red wrinkle and M9（polymerizing the genes that positively regulate the synthesis of anthocyanins cloned in the laboratory except the rll7gene）of commercial dark red lettuce were used as The control was grown for 30 days under the light intensity of 173μmol·m^-2·s^-1,81μmol·m^-2·s^-1and 29μmol·m^-2·s^-1,respectively,and the anthocyanin content was determined.The results showed that the dark red lettuce in this study could still synthesize anthocyanins under low light conditions,making the leaves appear dark red.Under the indoor light intensity(173μmol·m^-2·s^-1),the nutritional quality of dark red and light red lettuce was determined,and the results showed that the chlorophyll,soluble sugar,soluble protein and nitrate in the leaves of dark red and light red plants.There was no significant difference,while the content of total flavonoids in dark red plants was significantly higher than that in light red plants.Through the research of this topic,we can further understand the mechanism of the color change of lettuce leaves,improve the regulation network of anthocyanin synthesis in lettuce,and provide germplasm resources and theoretical basis for cultivating red lettuce suitable for planting under low light conditions in facilities and dwarfing ornamental.