Abstract
Wintersweet (Chimonanthus praecox) is a traditional Chinese ornamental plant that produces showy yellow flowers in winter. In addition to the common yellow-flowered variety group, there is a wintersweet group that produces unusual yellow-green tepals. Up to now, the mechanisms underlying the coloration of the yellow-green tepals are unknown. In this study, the results of chlorophyll content determination experiment showed that the chlorophyll content in wintersweet 'H37' (yellow-green variety) was significantly higher than that in 'H25' (yellow variety); the cellular ultrastructural observations suggested that the chloroplasts within 'H37' tepals cells could maintain their structure and function over a longer period during flower development. Moreover, the differentially expressed CpSGR1 gene and CpCHLD gene were screened by comparing the transcriptomes of 'H25' and 'H37'. Finally, the gene function verification experiments showed that, in chlorophyll metabolic pathway, CpSGR1 degraded chlorophyll, resulting in significant de-greening phenotypes, whereas CpCHLD could keep the leaves and flowers green. The findings provide new insights into the formation of the yellow-green tepal phenotype, as well as provide a research foundation for flower color breeding in wintersweet.