Identification of Chlorophyll Metabolism- and Photosynthesis-Related Genes Regulating Green Flower Color in Chrysanthemum by Integrative Transcriptome and Weighted Correlation Network Analyses

Abstract

Green chrysanthemums are difficult to breed but have high commercial value. The molecular basis for the green petal color in chrysanthemum is not fully understood. This was investigated in the present study by RNA sequencing analysis of white and green ray florets collected at three stages of flower development from the F1 progeny of the cross between Chrysanthemum × morifolium “Lüdingdang” with green-petaled flowers and Chrysanthemum vistitum with white-petaled flowers. The chlorophyll content was higher and chloroplast degradation was slower in green pools than in white pools at each developmental stage. Transcriptome analysis revealed that genes that were differentially expressed between the two pools were enriched in pathways related to chlorophyll metabolism and photosynthesis. We identified the transcription factor genes CmCOLa, CmCOLb, CmERF, and CmbHLH as regulators of the green flower color in chrysanthemum by differential expression analysis and weighted gene co-expression network analysis. These findings can guide future efforts to improve the color palette of chrysanthemum flowers through genetic engineering.

CmNAC73 Mediates the Formation of Green Color in Chrysanthemum Flowers by Directly Activating the Expression of Chlorophyll Biosynthesis Genes HEMA1 and CRD1

“…One of the important functions of leaves is photosynthesis, which takes place in chloroplasts. These photosynthetic organelles have also been observed in some green flowers by transmission electron microscopy [ 4 , 34 ]. In transgenic Arabidopsis and Nicotiana tabacum lines overexpressing SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC1 ) or SOC1-like , heat-stress induced the biogenesis of chloroplasts and the formation of green petals [ 35 ].…”

“…The total chlorophyll content of ray florets was determined as described by Fu et al [ 4 ]. Total carotenoid and total flavonoid contents were determined according to the methods of Potosí-Calvache et al [ 20 ] and Cao et al [ 21 ], respectively.…”

“…In the chlorophyll cycling process, chlorophyllide a oxygenase (CAO), chlorophyll(ide) b reductase (NYC1) and 7-hydroxymethyl chlorophyll-a reductase (HCAR) catalyze the conversion between chlorophyll-a and chlorophyll-b. Additionally, chlorophyll degradation is catalyzed by STAY-GREEN (SGR), pheophytin pheophorbide hydrolase (PPH), pheophorbide a oxygenase (PAO) and red chlorophyll catabolite reductase (RCCR) [ 4 ]. Mutations in genes involved in chlorophyll synthesis, such as HEMA , significantly inhibit chlorophyll synthesis and cause leaf yellowing [ 5 ], whereas mutations in the chlorophyll degradation gene SGR results in the stay-green phenotype where leaves remain green for a long time [ 6 ].…”

“…), the expression of CONSTANS-like 16 ( COL16 ) is highly associated with the chlorophyll content in different cultivars. In petunia ( Petunia × hybrida ), overexpression of the COL16 homolog, PhCOL16a , significantly enhanced the synthesis of chlorophyll [ 4 , 19 ], although the underlying mechanism remains unknown.…”

“…Chrysanthemum has been cultivated in China for more than 1500 years [ 4 ] and is considered an important flower around the world. Green chrysanthemums are very rare but also very popular in the market.…”