Study On Varieties Selection And Mechanism Of Leaf Colour Changing For Red Maple

As a colorful leaf tree species, red maple(Acer rubrum L.) is widely distributed in North America. The proporgation and mechanisms of leaf color change are the key for the introduction, breeding, and cultivation of red maple. Based on the introduction,ecological breeding and asexual propagation in the past 8 years, 5 vavieties with special traits are gained in Anhui province. Physiological assay and transcriptome sequencing of red maple are conducted to evaluate the mechanism of color change.The study provided the new germplasm resources and technologies for Chinese landscape diversity. The results are as follows:1) PropagationRed maple seed characteristics include both primary dormancy and secondary dormancy. Low temperature storage of seeds after harvesting(in refrigerator),increased the germination rate of seeds up to 65.8% after 42 d in the 4 ℃ wet sands the following spring. Red maple grows faster in Anhui province. If the native Acer serrulatum Hayata acted as the stock of red maple, 94% of grafted plants survived.The growth rate of the scion is significantly higher than that of the stock, and the grafted tumor came out in the third year. Study shows that the cutting depth of5 cm has the best effect on root growth. Cutting in late August, 82.3% of the red maple cuttings survived, and the next survival group is May. The 65% and80% moisture content groups of the cultivation substrate show the highest survived effect, and in the late period, the moisture content should be cut down to receive better root growth. The semi lignified shoots of red maple dipped in 100mg·L-1 ABT1#or 200 mg·L-1NAA for 6h showed the best results.2) Adaptability of introductionIn central Anhui province, red maple is sprouting in late March or early April.The bud and the red samara are visible in early April. Leaf is visible and become bigger in middle April. The samara is mature in early May, and fall off quickly. The leaf color changed gradually to golden yellow, red and other colors in middle and late October. The best period of leaf view is mid November. From late November to early December, the leaves fall off and trees go into the dormant period. The growth period of red maple is about 80 d longer than that in Ottawa, and red maple in Anhui province shows a bigger annual growth amount. During observation from 2007 to 2014, redmaple shows strong adaptability and resistance. At the beginning of 2011, having no rainfall for 130 d, 4-years-old plants can come through the dry period in the test base. From early July, to late August, a total of 38 days, last for extreme high temperature, more than 35 ℃, up to 40 ℃ with dry weather in the test base area, red maple survived in summer, but the leaf are yellow green, with severe burns. In the new habitat, ornamental traits of the introducted red maple from North American often change due to the new environment.3) Vavieties breedingRed maple is polygamodioecious, and the ornamental traits of the sexual propagation such as the leaf color, variated easily. Based on ecological breeding and asexual propagation, new varieties are developed to adapt the new environment. After years of breeding and regionalization test, the red color ’Zhongguohong’, ’Yanhong’,yellow color ‘Jinse- qiutian’ and ‘Chengzhimeng’, and leaf specific expression lines‘Jinmaihong’ are approved by the Anhui Forest Variety Approval Committee. After more than 5 years of observation, the ornamental characters of the improved vavieties such as leaf color are relatively stable in Anhui province. In addition, a three-leaf strain and 3 early– color-turned strains have been propagated, according to the leaf shape, leaf color and leaf number etc.4) Biochemical mechanism of leaf colour changingRed leaves are closely related to the contents of anthocyanin. Red, green and yellow leaves of sexual plants are analysed. After red maple turn color, the content of anthocyanin in red leaves increased significantly, which is more than 2 times than that in the green leaves. The content of anthocyanin in yellow leaves decreased significantly. Carotenoid concentration in red leaves and yellow leaves were significantly lower than that in green leaves. Chlorophyll concentration from large to small is as follows: green, red, yellow, and the difference is significant. Soluble sugar and p H value in different color leaf have no significant difference. The same tests are evaluated with ’Yanhong’, ’Jinseqiutian’ as material, to validate the analysis of the leaf color change, with similar results.5) Molecular mechanism of Acer rubrum L. ‘Yanhong’ leaf colourThe transcriptomes from ‘Yanhong’ red, green leaves were tested respectively by using the Illumina/Solexa high-throughput transcriptome sequencing technique. The original data of 4730 M, 4734 M was obtained. The percentages of Q20 are 98.15%,98.11%, and the contents of GC are 43.15%, 43.33% respectively. Short sequencesfrom sequencing are splited joint, and 143862 contigs, 175150 contigs are abtained from red leaves and green leaves with a mean length of 304 nt and 295 nt. 73556,87482 unigenes are installed by using Trinity software. The mean length of the unigenes is respectively 583 nt and 579 nt. N50 is respectively 1109 nt and 1127 nt. All unigenes are noted to NR, NT, Swiss-Prot, KEGG, COG, GO library, and 45637,34538, 31065, 29243, 23039, 32414 unigenes are difined respectively, with all difined unigene number 48245. Among them, the genes number related to anthocyanin synthesis pathway and flavonoid biosynthesis pathway is respectively 14 and 219. KEGG Pathway analysis shows that the red leaves(the control is green leaves) have up-regulated 2089 unigenes, and down-regulated 3410 unigenes.6) Anthocyanin synthesis pathway analysis and key gene miningIn the colored leaves of ‘Yanhong’, 5 of the 14 genes may be up-regulated expression in the anthocyanin synthesis pathway and 53 of the 219 genes in the flavonoid pathway. There branchs of anthocyanin synthesis pathway genes F3 H, F3’H,F3’5’H and DFR, are found in the transcriptome database, which underlines‘Yanhong’ has 3 branchs of anthocyanin biosynthesis pathway. Upstream of anthocyanin synthesis gene, CHS, CHI, and ANS gene, and modification gene 3AT may synergistically up-regulated. Anthocyanin is unstable in neutral p H, modification can improve its stability and transport. In the transcriptome database, only several modification gene such as 3AT, UGT75C1, FMT etc. are found. Compared with such anthocyanin glycosylation genes in petals in other species, the glycosylation genes are less. The limited glycosylation genes may cause incomplete anthocyanin glycosylation. The genes and enzymes will be quantitatively analysised and verificated. This study may provide reference for the molecular improvement of leaf color for red maple.