Pantranscriptome combined with phenotypic quantification reveals germplasm kinship and regulation network of bract color variation in Bougainvillea

Huaxing Huang; Hongli Ji; Song Ju; Wei Lin; Jing Li; Xuanrui Lv; Lixian Lin; Lijin Guo; Dongliang Qiu; Jianyong Yan; Xiaokai Ma

doi:10.3389/fpls.2022.1018846

Pantranscriptome combined with phenotypic quantification reveals germplasm kinship and regulation network of bract color variation in Bougainvillea

Front Plant Sci. 2022 Nov 17:13:1018846. doi: 10.3389/fpls.2022.1018846. eCollection 2022.

Authors

Huaxing Huang^{1

2}, Hongli Ji³, Song Ju^{1

4}, Wei Lin⁴, Jing Li^{1

5}, Xuanrui Lv^{1

6}, Lixian Lin^{1

6}, Lijin Guo⁷, Dongliang Qiu⁵, Jianyong Yan², Xiaokai Ma^{1

8}

Affiliations

¹ Center for Genomics and Biotechnology, School of Future Technology, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fuzhou, China.
² Yuanshan Institute of Bougainvillea in Longhai, Zhangzhou, China.
³ Vegetable and Flower Institute, Jiangxi Academy of Agricultural Sciences, Nanchang, China.
⁴ College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, China.
⁵ College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, China.
⁶ College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, China.
⁷ International Magnesium Institute, School of Future Technology, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fuzhou, China.
⁸ Key Laboratory of Orchid Conservation and Utilization of National Forestry and Grassland Administration at College of Landscape Architecture, Fujian Agriculture and Forestry University, Fuzhou, China.

Abstract

Bracts are the metamorphic non-flower organ in angiosperm plants. The variation of the color and shape of bracts was found to be neo-functionalized (i.e., similar to petals), garnering research interest as a pollinator attractor. Bougainvillea is known for its specialized, large, and colorful bracts, which contrast with its tiny colorless flowers. As a plant whose bracts vary greatly in terms of coloration, the molecular mechanisms for Bougainvillea bract coloration and polychroism are largely unknown. The lack of genomic information for Bougainvillea largely hinders studies into the evolution and genetic basis of bract color variation. In this study, a pan-transcriptome of bracts obtained from 18 Bougainvillea glabra accessions was employed to investigate the global population-level germplasm kinship and the gene regulation network for bract color variation. Our results showed that the bracts of B. glabra accessions have largely differentiated International Commission on Illumination (CIE) L-a-b values. Moreover, germplasm kinship detected using principal component analysis, phylogeny, and admixture analysis showed three optimal subgroups, two of them distinctly clustered, which were not directly correlated with bract color variation at the population level. Differentially expressed genes (DEGs) between accessions of high vs. low L-a-b values revealed several considerable upregulated genes related to bract color L-a-b variation. A weighted gene co-expression network was constructed, and eight co-expressed regulation modules were identified that were highly correlated with variation in bract CIE L-a-b color values. Several candidate DEGs and co-expressed hub genes (e.g., GERD, SGR, ABCA3, GST, CYP76AD1, CYP76C, and JAZ) that were tightly associated with bract color variation were eventually determined responsible for L-a-b colorations, which might be the core regulation factors contributing to the B. glabra bract color variation. This study provides valuable insights into the research on germplasm kinship, population-level pan-transcriptome expression profiles, and the molecular basis of color variation of key innovative bracts in horticultural Bougainvillea.

Keywords: Bougainvillea bracts; co-expression network; color variation; gene regulation; pan-transcriptome.