Whole-genome Identification And Expression Analysis Of Anthocyanin Biosynthesis-related Genes In Brassica Napus

As a flavonoid metabolite,anthocyanin confers different colors in plants and plays an important role in stress resistance,human health care and so on.Brassica napus is the widely cultivated oil crop in the world,however,few genes related to anthocyanin synthesis have been identified due to the lack of purple leaf mutants,thus the formation mechanism of the purple leaf color remains unclear.Herein,the phenotypic,whole-genome comparative identification,RNA-seq,and Bulked Segregant Analysis（BSA）were performed in parental inbred lines with purple leaf（PL）and green leaf（GL）,as well as their hybrid F₁ generation.The main research results are exhibited as following:1.Phenotype of B.napus with purple leaves.Freehand sections of B.napus with purple leaves indicated that the purple pigment was mainly accumulated in the upper epidermis of leaves,and the accumulation level was significantly higher than that in the F₁ generation,whereas no anthocyanin pigment deposition was observed in green leaves.During the development of purple leaf mutants,the leaf color changed from purple to dark purple,then faded to light purple,and finally turned to green.2.Measuring of anthocyanin content.Measuring of total anthocyanin content at different developmental stages of PL,GL,and F₁ suggested that the average in PL was significantly higher than F₁ and GL.Meanwhile the total anthocyanin content in PL increased at initial stage but decreased after that,which was consistent with the change of phenotype.3.Whole-genome identification of anthocyanin biosynthetic genes.A total of 151 anthocyanin biosynthetic genes were identified in B.napus through comparative whole-genome identification,which was expanded by about 3 times as compared with 41 anthocyanin biosynthetic genes in A.thaliana.Chromosomal localization and syntenic analysis shown that the anthocyanin biosynthetic genes in B.napus was mainly expanded following the whole-genome duplication and tandem duplication.4.Comparative transcriptome analysis.The gene expression analysis of PL,GL,and F₁ at 41,91,and 101 days found that 22 anthocyanin biosynthetic genes were differentially expressed.Among them,most were late biosynthetic genes and regulatory genes.Especially,the up-regulation of TT8 and its target genes（such as DFR,ANS,UFGT,etc.） might result in the anthocyanin accumulation in purple leaves（41–91d）.While down-regulation of these genes in late developmental stage（after 101d）might result in the anthocyanin decreasing and color fading to green.5.Initial mapping of genes related to leaf color.An F₂ population which was constructed by crossing PL and GL showed that purple leaf was a dominant character controlled by a single gene.BSA-seq analysis found that the genes were located on chromosome A03 and included a total of 105 candidate genes in the interval.Our study has provided some insight to understand the molecular mechanism of anthocyanin accumulation and might contribute to the genetic improvement of high anthocyanin cultivars in B.napus.