Research On The Mechanism Of Flower Pigment Mutation Induced By Carbon Ions In Geranium(Pelargonium × Hortorum)

As the important economic indicator for ornamental plants, flower color becomes the primary target for ornamental improving and breeding. In this study, one flower color mutant was obtained using carbon ion irradiation, which could stably inherited by cutting vegetative propagation. In order to elucidate the underlying mutation mechanism of flower color variation in mutant, the morphological characteristics, factors on flower coloration, pigment components and quantities, the differential expression of key genes of anthocyanin biosynthesis was systemic analyzed. Meanwhile, RNA sequencing technology was used to detect the transcriptome information of Pelargonium, unigenes were identified and the genes related to the formation of pigment were speculated. These results explained the mechanism of coloration change in mutant induced by carbon ions and provided the research foundation for the follow-up design and color improvement in Pelargonium. The main results of our research are described as follows:1. Shoots of geranium were exposed to carbon ions and one flower color mutant was obtained at dosage of 30 Gy. The color of petal, peduncle, pistil and stamen and physiological indexes of mutant displayed significant differences with wild type. Anatomical structure observations showed that the salmon pigments fully filled with the epidermal cells of RWT, while only a small number of pale pink pigments in LPM.2. Genome DNA fingerprint detected by random amplified polymorphic DNA markers showed that there were 66 polymorphism amplified bands between wild type and mutant, among which 18 bands were particular amplified in mutant, and 48 bands were not presented. The ratio of different bands between wild type and mutant reached up to 13.2%.3. Based on the analysis of compositions and quantities of flavonoid between RWT and LPM by HPLC, it was suggested that the main pigments determined the flower color of RWT were abundant pelargonidin and bits of cyanidin and delphinidin. While the unique pigment detected in LPM was cyanidin. The core reason of depigmentation in LPM was the absence of pelargonidin and delphinidin. Both suppressed expression of early genes CHS, CHI and late gene ANS blocked the biosynthesis of anthocyanin, which seemed to be the crucial reason for the color change of LPM.4. RNA sequencing was executed to establish the transcriptome databases of Pelargonium and 89817 unigenes were obtained. In total, 1503 different expression genes were identified between orange-red wild type and light pink mutant, among which 700 genes were up-regulated while 803 were down-regulated in mutant. Blasted with the public databases, the maximum number of unigenes was mapped to Signal P. DEGs were highly enriched in the flavonoid biosynthesis.5. 177 unigenes were predicted homologs to color-related genes, including anthocyanin biosynthesis genes, anthocyanin modification genes,flavone and flavonol biosynthesis genes and anthocyanin transport genes. Moreover, several transcription factors were also supposed, which related to flower color regulation. The detective results of expression levels of the structure genes and transcription factors by Q-PCR were consistent with the analysis of transcriptome. Comparing with the wild type, the down-regulations were the main expression pattern of genes in mutant.