Abstract
Chrysanthemum is one of the most beautiful and popular flowers in the world, and the flower color is an important ornamental trait of chrysanthemum. Compared with other flower colors, green flowers are relatively rare. The formation of green flower color is attributed to the accumulation of chlorophyll; however, the regulatory mechanism of chlorophyll metabolism in chrysanthemum with green flowers remains largely unknown. In this study, we performed Illumina RNA sequencing on three chrysanthemum materials, Chrysanthemum vestitum and Chrysanthemum morifolium cultivars ‘Chunxiao’ and ‘Green anna’, which produce white, light green and dark green flowers, respectively. Based on the results of comparative transcriptome analysis, a gene encoding a novel NAC family transcription factor, CmNAC73, was found to be highly correlated to chlorophyll accumulation in the outer whorl of ray florets in chrysanthemum. The results of transient overexpression in chrysanthemum leaves showed that CmNAC73 acts as a positive regulator of chlorophyll biosynthesis. Furthermore, transactivation and yeast one-hybrid assays indicated that CmNAC73 directly binds to the promoters of chlorophyll synthesis-related genes HEMA1 and CRD1. Thus, this study uncovers the transcriptional regulation of chlorophyll synthesis-related genes HEMA1 and CRD1 by CmNAC73 and provides new insights into the development of green flower color in chrysanthemum and chlorophyll metabolism in plants.
Highlights
Color is an important ornamental trait in plants
The results showed that the expression of HEMA1, CHLI1, CHLH1, CRD1 and PORA1 was significantly inhibited by Abscisic acid (ABA) (Figure S5)
We found a novel chrysanthemum named the Cluster-35308.177654 (NAC) gene, CmNAC73, whose expression was repressed by ABA, and its transient overexpression in chrysanthemum leaves delayed leaf senescence by activating several chlorophyll synthesis-related genes, including HEMA1, CHLI1, CHLM1, CRD1 and PORA1 (Figures 6 and 7)
Summary
Color is an important ornamental trait in plants. Flower color plays an important role in the co-evolution of plants and insects, as flowers use their color to attract insects or birds for pollination [1]. Plants often use bright colors to protect themselves from herbivores. At high altitudes, flowers usually accumulate high levels of anthocyanin, which protects the plants from damage by ultraviolet (UV) radiation [2]. Flower color is influenced by carotenoids and chlorophyll. Since chlorophyll plays an important role in photosynthesis, a number of studies have focused on the mechanism of chlorophyll metabolism and regulation in leaves, which is of great importance in delaying leaf senescence and increasing the crop yield [3]
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