Comparative transcriptome analyses reveal genes related to pigmentation in the petals of a flower color variation cultivar of Rhododendron obtusum.

Xiaobo Sun,Zheng Xiao,Haidong Gao,Lisi He,Huimin Zhou,Zhenhao Guo,Chang Li,Jiale Su,Xiaoqing Liu

doi:10.1007/s11033-021-07070-w

Abstract

Rhododendron is an important woody ornamental plant, and breeding varieties with different colors is a key research goal. Although there have been a few reports on the molecular mechanisms of flower colors and color patterning in Rhododendron, it is still largely unknown what factors regulate flower pigmentation in Rhododendron. In this study, the flower color variation cultivar 'Yanzhi Mi' and the wild-type (WT) cultivar 'Dayuanyangjin' were used as research objects, and the pigments and transcriptomes of their petals during five flower development stages were analyzed and compared. The results showed that derivatives of cyanidin, peonidin and pelargonidin might be responsible for the pink color of mutant petals and that the S2 stage was the key stage of flower color formation. In total, 412,910 transcripts and 2780 differentially expressed genes (DEGs) were identified in pairwise comparisons of WT and mutant petals. GO and KEGG enrichment analyses of the DEGs showed that 'DNA-binding transcription factor activity', 'Flavonoid biosynthesis' and 'Phenylpropanoid biosynthesis' were more active in mutant petals. Early anthocyanin pathway candidate DEGs (CHS3-CHS6, CHI, F3Hs and F3'H) were significantly correlated and were more highly expressed in mutant petals than in WT petals in the S2 stage. An R2R3-MYB unigene (TRINITY_DN55156_c1_g2) was upregulated approximately 10.5-fold in 'Yanzhi Mi' petals relative to 'Dayuanyangjin' petals in the S2 stage, and an R2R3-MYB unigene (TRINITY_DN59015_c3_g2) that was significantly downregulated in 'Yanzhi Mi' petals in the S2 stage was found to be closely related to Tca MYB112 in cacao. Taken together, the results of the present study could shed light on the molecular basis of anthocyanin biosynthesis in two Rhododendron obtusum cultivars and may provide a genetic resource for breeding varieties with different flower colors.

Highlights

Rhododendron is the largest genus of the family Ericaceae, and important ornamental woody plants, contains approximately 1,000 species and thousands of commercial hybrids [1]
chalcone synthase (CHS) and dihydroflavonol 4-reductase (DFR) genes were cloned from R. simsii hybrids, and the expression of these two genes has been examined in eight azalea cultivars, and the results showed that there was no significant correlation between flower color phenotype and expression levels of the CHS and DFR genes [24,25]
The results indicated that anthocyanins might play vital roles in pink flower color formation of ‘Yanzhi Mi’

Summary

Introduction

Rhododendron is the largest genus of the family Ericaceae, and important ornamental woody plants, contains approximately 1,000 species and thousands of commercial hybrids [1]. As an important ornamental trait, greatly affects the economic value of Rhododendron. Previous studies have shown that many factors (cell shape, copigmentation, pH, environmental conditions, and so forth) affect petal colors, but in which, pigment composition is the most important [3]. The petals of Rhododendron flowers contain flavonols and anthocyanins as the major pigments [4]. The flavonol composition and content have some effect on flower color by copigmentation, but might not play a major role in coloration [8,9].The major anthocyanidins of Rhododendron petals are cyanidin, peonidin, delphinidin, petunidin, malvidin, and pelargonidin [4,10,11]. Anthocyanin constitution and content are fundamental elements that determine Rhododendron flower colors [4,9,13].

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